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1. 4 20 4 Attempt keyboard interactive authentication The SSH 2 equivalent of TIS authentication is called keyboard interactive It is a flexible authentication method using an arbitrary sequence of requests and responses so it is not only useful for challenge response mechanisms such as S Key but it can also be used for for example asking the user for a new password when the old one has expired PuTTY leaves this option enabled by default but supplies a switch http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 52 of 131 to turn it off in case you should have trouble with it 4 20 5 Allow agent forwarding This option allows the SSH server to open forwarded connections back to your local copy of Pageant If you are not running Pageant this option will do nothing See chapter 9 for general information on Pageant and section 9 4 for information on agent forwarding Note that there is a security risk involved with enabling this option see section 9 5 for details 4 20 6 Allow attempted changes of username in SSH 2 In the SSH 1 protocol it is impossible to change username after failing to authenticate So if you mis type your username at the PuTTY login as prompt you will not be able to change it except by restarting PuTTY The SSH 2 protocol _does_ allow changes of username in principle but does not make it mandatory for SSH 2 servers to
2. As well as specifying a value in bytes the following shorthand can be used Ik specifies 1 kilobyte 1024 bytes IM specifies 1 megabyt 1024 kilobytes IG specifies 1 gigabyte 1024 megabytes Disabling data based rekeys entirely is a bad idea The integrity and to a lesser extent confidentiality of the SSH 2 protocol depend in part on rekeys occuring before a 32 bit packet sequence number wraps around Unlike time based rekeys data based rekeys won t occur when the SSH connection is idle so they shouldn t cause the same problems The SSH 1 protocol incidentally has even weaker http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 51 of 131 integrity protection than SSH 2 without rekeys 4 20 The Auth panel The Auth panel allows you to configure authentication options for SSH sessions 4 20 1 Bypass authentication entirely In SSH 2 it is possible to establish a connection without using SSH s mechanisms to identify or authenticate oneself to the server Some servers may prefer to handle authentication in the data channel for instance or may simply require no authentication whatsoever By default PuTTY assumes the server requires authentication most do and thus must provide a username If you find you are getting unwanted username prompts you could try checking this option This option only affects SSH 2 connections
3. By default PuTTY only uses the server supplied _window_ title and ignores the icon title entirely If for some reason you want to see both titles check the box marked Separate window and icon titles If you do this PuTTY s window title and Taskbar caption will change into the server supplied icon title if you minimise the PuTTY window and change back to the server supplied window title if you restore it If the server has not bothered to supply a window or icon title none of this will happen 4 9 2 Warn before closing window If you press the Close button in a PuTTY window that contains a running session PuTTY will put up a warning window asking if you really meant to close the window A window whose session has already terminated can always be closed without a warning If you want to be able to close a window quickly you can disable the Warn before closing window option 4 9 3 Window closes on ALT F4 By default pressing ALT F4 causes the window to close or a warning box to appear see section 4 9 2 If you disable the Window closes on ALT F4 option then pressing ALT F4 will simply send a key sequence to the server 4 9 4 System menu appears on ALT Space If this option is enabled then pressing ALT Space will bring up the PuTTY window s menu like clicking on the top left corner If it is disabled then pressing ALT Space will just send ESC SPACE
4. Use font in OEM mode only is more reliable than that but can miss out other characters from the main character set 4 10 5 Controlling copy and paste of line drawing characters By default when you copy and paste a piece of the PuTTY screen that contains VT100 line and box drawing characters PuTTY will paste them in the form they appear on the screen either Unicode line drawing code points or the poor man s line drawing characters and The checkbox Copy and paste VT100 line drawing chars as lqqqk disables this feature so line drawing characters will be pasted as the ASCII characters that were printed to produce them This will typically mean they come out mostly as q and x with a scattering of jklmntuvw at the corners This might be useful if you were trying to recreate the same box layout in another program for example Note that this option only applies to line drawing characters which _were_ printed by using the VT100 mechanism Line drawing characters that were received as Unicode code points will paste as Unicode always http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 37 of 131 4 11 The Selection panel The Selection panel allows you to control the way copy and paste work in the PuTTY window 4 11 1 Pasting in Ric If you enable PuTTY will wri as the actual h Text Format Paste to clipboard in RTF as well as plain te
5. achine if it doesn t the manual for the X server should tell you hat it does do You should then tick the Enable X11 forwarding box in the Tunnels panel see section 4 22 before starting your SSH session The X display location box is blank by default which means that PuTTY will try to use a sensible default such as 0 which is the usual display location where your X server will be installed If that needs changing then change it Now you should be able to log in to the SSH server as normal To check that X forwarding has been successfully negotiated during connection startup you can check the PuTTY Event Log see section 3 1 3 1 It should say something like this 2001 12 05 17 22 01 Requesting X11 forwarding 2001 12 05 17 22 02 X11 forwarding enabled http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 10 of 131 If the remote system is Unix or Unix like you should also be able to see that the DISPLAY environment variable has been set to point at display 10 or above on the SSH server machine itself fred unixbox echo SDISPLAY unixbox 10 0 If this works you should then be able to run X applications in the remote session and have them display their windows on your PC Note that if your PC X server requires authentication to connect then PuTTY cannot currently support it If this is a problem for you you should mail the PuTTY authors and give deta
6. This option is enabled by default http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 22 of 131 4 2 4 2 Omit session data When checked all decrypted session data is omitted this is defined as data in terminal sessions and in forwarded channels TCP X11 and authentication agent This will usually substantially reduce the size of the resulting log file This option is disabled by default 4 3 The Terminal panel he Terminal configuration panel allows you to control the behaviour of PuTTY s terminal emulation 4 3 1 Auto wrap mode initially on Auto wrap mode controls what happens when text printed in a PuTTY window reaches the right hand edge of the window With auto wrap mode on if a long line of text reaches the right hand edge it will wrap over on to the next line so you can still see all the text With auto wrap mode off the cursor will stay at the right hand edge of the screen and all the characters in the line will be printed on top of each other If you are running a full screen application and you occasionally find the screen scrolling up when it looks as if it shouldn t you could try turning this option off Auto wrap mode can be turned on and off by control sequences sent by the server This configuration option controls the _default_ state which will be restored when you reset the terminal see section 3 1 3 6 However if
7. D 9 Keystrokes sent to the server wherever possible In almost all cases PuTTY sends keystrokes to the server Even weird keystrokes that you think should be hot keys controlling PuTTY Even Alt F4 or Alt Space for example If a keystroke has a well defined escape sequence that it could usefully be sending to the server then it should do so or at the very least it should be configurably able to do so To unconditionally turn a key combination into a hot key to control PuTTY is almost always a design error If a hot key is really truly required then try to find a key combination for it which _isn t_ already used in existing PuTTYs either it sends nothing to the server or it sends the same thing as some other combination Even then be prepared for the possibility that one day that key combination might end up being needed to send something to the server so make sure that there s an alternative way to invoke whatever PuTTY feature it controls D 10 640x480 friendliness in configuration panels There s a reason we have lots of tiny configuration panels instead of a few huge ones and that reason is that not everyone has a 1600x1200 desktop 640x480 is still a viable resolution for running Windows and indeed it s still the default if you start up in safe mode so it s still a resolution we care about Accordingly the PuTTY configuration box and the PuTTYgen control window ar
8. D 3 Multiple sessions per process on some platforms Some ports of PuTTY notably the in progress Mac port are constrained by the operating system to run as a single process potentially managing multiple sessions Therefore the platform independent parts of PuTTY never use global variables to store per session data The global variables that do exist are tolerated because they are not specific to a particular login session flags defines properties that are expected to apply equally to _all_ the sessions run by a single PuTTY process the random number state in sshrand c and the timer list in timing c serve all sessions equally and so on But most data is specific to a particular network session and is therefore stored in dynamically allocated data structures and pointers to these structures are passed around between functions latform specific code can reverse this decision if it likes The indows code for historical reasons stores most of its data as obal variables That s OK because _on Windows_ we know there is nly one session per PuTTY process so it s safe to do that But hanges to the platform independent code should avoid introducing obal variables unless they are genuinely cross session aang D 4 C not C PuTTY is written entirely in C not in C We have made _some_ effort to make it easy to compile our code using a C compiler notably our snew s
9. The first example go rwx removes read write and execut permissions for members of the owning group and everybody else so the only permissions left are the ones for the file owner utw adds write permission for the file owner The second example at r adds read permission for everybody to all files and directories starting with public In addition to all this there are a few extra special cases for Unix systems On non Unix systems these are unlikely to be useful You can specify u s and u s to add or remove the Unix set user ID bit This is typically only useful for special purposes refer to your Unix documentation if you re not sure about it You can specify g s and g s to add or remove the Unix set group ID bit On a file this works similarly to the set user ID bit see your Unix documentation again on a directory it ensures that files created in the directory are accessible by members of the group that owns the directory You can specify t and t to add or remove the Unix sticky bit When applied to a directory this means that the owner of a file in that directory can delete the file whereas normally only the owner of the _directory_ would be allowed to The del command delete remote files To delete a file on the server type del and then the filename or filenames del oldfile dat del filel txt file
10. To enable agent forwarding first start Pageant Then set up a PuTTY SSH session in which Allow agent forwarding is enabled see section 4 20 5 Open the session as normal Alternatively you can use the A command line option see section 3 8 3 10 for details If this has worked your applications on the server should now have access to a Unix domain socket which the SSH server will forward back to PuTTY and PuTTY will forward on to the agent To check that this has actually happened you can try this command on Unix server machines unixbox S echo SSSH_AUTH_SOCK tmp ssh XXNP18J0z agent 28794 unixbox S If the result line comes up blank agent forwarding has not been enabled at all Now if you run ssh on the server and use it to connect through to another server that accepts one of the keys in Pageant you should be able to log in without a password unixbox ssh v otherunixbox Peal debug next auth method to try is publickey http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 89 of 131 debug userauth_pubkey_agent trying agent key my putty key debug ssh userauth2 successful method publickey peel If you enable agent forwarding on _that_ SSH connection as well see the manual for your server side SSH client to find out how to do this your authentication keys will still be available on the next machine you connect to two SSH connections away from where they re ac
11. If you want to distribute PuTTY alongside your own application for use with that application or if you want to distribute PuTTY within your own organisation then we recommend but do not insist that you offer your own first line technical support to answer questions about the interaction of PuTTY with your environment If your users mail us directly we won t be able to tell them anything useful about your specific setup If you want to use parts of the PuTTY source code in another program then it might be worth mailing us to talk about technical details but if all you want is to ask permission then you don t need to bother You already have permission If you just want to link to our web site just go ahead It s not clear that we _could_ stop you doing this even if we wanted to B 8 Mirroring the PuTTY web site Mirrors of the PuTTY web site are welcome especially in regions not well covered by existing mirrors However if you re in a region that is already well served by mirrors you should consider whether yet another one will be worth the effort Please don t bother asking us for permission before setting up a mirror You already have permission If you mail us _after_ you have set up the mirror and checked that it works and remember to let us know which country your mirror is in then we ll add it to the Mirrors page on the PuTTY website If you have technical questions about the process of
12. Can you write us a formal notice of permission to use PuTTY We could in principle but it isn t clear what use it would be If you think there s a serious chance of one of the PuTTY copyright holders suing you which we don t you would presumably want a signed notice from _all_ of them and we couldn t provide that even if we wanted to because many of the copyright holders are peopl who contributed some code in the past and with whom we subsequently lost contact Therefore the best we would be able to do _even in theory_ would be to have the core development team sign the document which wouldn t guarantee you that some other copyright holder might not sue See also question A 9 12 for another reason why we don t want to do this sort of thing Can you sign _anything_ for us Not unless there s an incredibly good reason http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 A 9 13 A 9 14 Page 115 of 131 We are generally unwilling to set a precedent that involves us having to enter into individual agreements with PuTTY users We estimate that we have literally _millions_ of users and we absolutely would not have time to go round signing specific agreements with every one of them So if you want us to sign something specific for you you might usefully stop to consider whether there s anything special that distinguishes you from 999 999 other users and therefore any reason we should be wi
13. Public key authentication both RSA and DSA in SSH 2 is new in version 0 52 A 2 2 Does PuTTY support reading OpenSSH or ssh com SSH 2 private key files PuTTY doesn t support this natively see the wishlist entry for reasons why not but as of 0 53 PuTTYgen can convert both OpenSSH and ssh com private key files into PuTTY s format A 2 3 Does PuTTY support SSH 1 Yes SSH 1 support has always been available in PuTTY A 2 4 Does PuTTY support local echo Yes Version 0 52 has proper support for local echo In version 0 51 and before local echo could not be separated from local line editing where you type a line of text locally and it is not sent to the server until you press Return so you have the chance to edit it and correct mistakes _before_ the server sees it New in version 0 52 local echo and local line editing are separate options and by default PuTTY will try to determine automatically WwW S P e hether to enable them or not based on which protocol you have elected and also based on hints from the server If you have a roblem with PuTTY s default choice you can force each option to be nabled or disabled as you choose The controls are in the Terminal panel in the section marked Line discipline options A 2 5 Does PuTTY support storing settings so I don t have to change them every time Yes all of PuTTY s settings can be saved in named session profiles You can also chan
14. box you ca button by specifying n also optionally enter an IP for instance 127 0 0 5 79 tion on how this works and its restrictions In place of port numbers you can enter service names if they are known to the local system For instance in the Destination box you could enter popserver example com pop3 You can modify the currently active set of port forwardings in mid session using Change Settings a local or dynamic port forwarding in mid session http the earth li sgtatham putty 0 60 puttydoc txt see section 3 1 3 4 If you delete PuTTY will stop 7 11 2008 Page 56 of 131 listening for connections on that port so it can be re used by another program If you delete a remote port forwarding note that he SSH 1 protocol contains no mechanism for asking the server to stop listening on a remote port The SSH 2 protocol does contain such a mechanism but not all SSH servers support it In particular OpenSSH does not support it in any version earlier than 3 9 If you ask to delete a remote port forwarding and PuTTY cannot make the server actually stop listening on the port it will instead just start refusing incoming connections on that port Therefore although the port cannot be reused by another program you can at least be reasonably sure that server side programs can no longer access the service at your end of the port forwarding If you
15. mv file dir mv filel dirl file2 dir2 MV x Fh The rename and ren commands work exactly the same way as mv 6 2 19 The command run a local Windows command You can run local Windows commands using the command This is the only PSFTP command that is not subject to the command quoting rules given in section 6 2 1 If any command line begins with the I character then the rest of the line will be passed straight to Windows without further translation For example if you want to move an existing copy of a file out of the way before downloading an updated version you might type psftp gt ren myfile dat myfile bak psftp gt get myfile dat using the Windows ren command to rename files on your local PC 6 3 Using public key authentication with PSFTP Like PuTTY PSFTP can authenticate using a public key instead of a password There are thr ways you can do this Firstly PSFTP can use PuTTY saved sessions in place of hostnames So you might do this Run PuTTY and create a PuTTY saved session see section 4 1 2 which specifies your private key file s section 4 20 7 You will probably also want to specify a username to log in as see section 4 14 1 In PSFTP you can now use the name of the session instead of a hostname type psftp sessionname where sessionname is replaced by the name of your saved session Secondly you can supply the name of a private key file on th
16. This and other special characters are specified using cC notation for Ctrl C and so on Use lt 27 gt or lt 0x1B gt to specify a character numerically and to get a literal Other non control characters are denoted by themselves Leaving the box entirely blank indicates that _no_ character should be assigned to the specified function supported by all servers QUIT is a special character that usually forcefully ends the http the earth li sgtatham putty 0 60 puttydoc txt although this may not be 7 11 2008 Page 54 of 131 current process on the server SIGQUIT On many servers its default setting is Ctrl backslash which is easy to accidentally invoke on many keyboards If this is getting in your way you may want to change it to another character or turn it off entirely Boolean modes such as ECHO and ICANON can be specified in PuTTY in a variety of ways such as true false yes no and 0 1 Terminal speeds are configured elsewhere s section 4 14 3 4 22 The X11 panel The X11 panel allows you to configure forwarding of X11 over an SSH connection If your server lets you run X Window System applications X11 forwarding allows you to securely give those applications access to a local X display on your PC To enable X11 forwarding check the Enable X11 forwarding box If your X display is somewhere unusual you will need to enter its location in the X dis
17. http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 83 of 131 change the comment and save it again 8 2 7 Setting a passphrase for your key The Key passphrase and Confirm passphrase boxes allow you to choose a passphrase for your key The passphrase will be used to encrypt the key on disk so you will not be able to use the key without first entering the passphrase When you save the key PuTTYgen will check that the Key passphrase and Confirm passphrase boxes both contain exactly the same passphrase and will refuse to save the key otherwis If you leave the passphrase fields blank the key will be saved unencrypted You should _not_ do this without good reason if you do your private key file on disk will be all an attacker needs to gain access to any machine configured to accept that key If you want to be able to passwordless loginlog in without having to type a passphrase every time you should consider using Pageant chapter 9 so that your decrypted key is only held in memory rather than on disk Under special circumstances you may genuinely _need_ to use a key with no passphrase for example if you need to run an automated batch script that needs to make an SSH connection you can t be there to type the passphrase In this case we recommend you generate a special key for each specific batch script or whatever that needs one and on the server side you sh
18. D 4096 load mysession For general information on port forwarding see section 3 5 These options are not available in the file transfer tools PSCP and PSFTP 3 8 3 6 m read a remote command or script from a file The m option performs a similar function to the Remote command box in the SSH panel of the PuTTY configuration box see section 4 18 1 However the m option expects to be given a local file name and it will read a command from that file http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 15 of 131 With some servers particularly Unix systems you can even put multiple lines in this file and execute more than one command in sequence or a whole shell script but this is arguably an abuse and cannot be expected to work on all servers In particular it is known _not_ to work with certain embedded servers such as Cisco routers This option is not available in the file transfer tools PSCP and PSE LP 3 8 3 7 P specify a port number The P option is used to specify the port number to connect to If you have a Telnet server running on port 9696 of a machine instead of port 23 for example putty telnet P 9696 host name plink telnet P 9696 host name Note that this option is more useful in Plink than in PuTTY because in PuTTY you can write putty telnet host name 9696 in any case This option is equivalent to the port number control in the Session
19. Enable compression This enables data compression in the SSH connection data sent by the server is compressed before sending and decompressed at the client end Likewise data sent by PuTTY to the server is compressed first and the server decompresses it at the other end This can help make the most of a low bandwidth connection Preferred SSH protocol version This allows you to select whether you would like to use SSH protocol version 1 or version 2 PuTTY will attempt to use protocol 1 if the server you connect to does not offer protocol 2 and vice versa If you select 1 only or 2 only here PuTTY will only connect if the server you connect to offers the SSH protocol version you have specified Encryption algorithm selection PuTTY supports a variety of different encryption algorithms and allows you to choose which one you prefer to use You can do this by dragging the algorithms up and down in the list box or moving them using the Up and Down buttons to specify a preference order When you make an SSH connection PuTTY will search down the list from the top until it finds an algorithm supported by the server and then use that PuTTY currently supports the following algorithms AES Rijndael 256 192 or 128 bit SDCTR or CBC SSH 2 only Arcfour RC4 256 or 128 bit stream cipher SSH 2 only Blowfish 256 bit SDCTR SSH 2 only or 128 bit CBC Triple
20. The lengths should only ever differ by one and there is no perceptible drop in security as a result DSA keys are not created by multiplying primes together so they hould always be exactly the length you asked for n 8 2 4 The Generate button Once you have chosen the type of key you want and the strength of the key press the Generate button and PuTTYgen will begin the process of actually generating the key First a progress bar will appear and PuTTYgen will ask you to move the mouse around to generate randomness Wave the mouse in circles over the blank area in the PuTTYgen window and the progress bar will gradually fill up as PuTTYgen collects enough randomness You don t need to wave the mouse in particularly imaginative patterns although it can t hurt PuTTYgen will collect enough randomness just from the fine detail of _exactly_ how far the mouse has moved each time Windows samples its position When the progress bar reaches the end PuTTYgen will begin creating the key The progress bar will reset to the start and gradually move up again to track the progress of the key generation It will not move evenly and may occasionally slow down to a stop this is unfortunately unavoidable because key generation is a random process and it is impossible to reliably predict how long it will take When the key generation is complete a new set of controls will
21. This may help PSFTP s behaviour when it is used in automated scripts using batch if something goes wrong at connection time the batch job will fail rather than hang Running PSFTP Once you have started your PSFTP session you will see a psftp gt prompt You can now type commands to perform file transfer functions This section lists all the available commands General quoting rules for PSFTP commands Most PSFTP commands are considered by the PSFTP command interpreter as a sequence of words separated by spaces For example the command ren oldfilename newfilename splits up into three words ren the command name oldfilename the name of the file to be renamed and newfilename the new name to give the file Sometimes you will need to specify file names that _contain_ spaces In order to do this you can surround the file name with double quotes This works equally well for local file names and remote file names psftp gt get spacey file name txt save it under this name txt The double quotes themselves will not appear as part of the file names they are removed by PSFTP and their only effect is to stop the spaces inside them from acting as word separators If you need to _use_ a double quote on some types of remote system such as Unix you are allowed to use double quotes in file names you can do this by doubling it This works both inside and outside doubl
22. a fix you can download _However_ we ve been told that SP2 _also_ fixes the bug that means you need to use non 127 0 0 1 addresses to forward Terminal Services in the first place PSFTP commands seem to be missing a directory separator slash Some people have reported the following incorrect behaviour with PSFTP psftp gt pwd Remote directory is dirl dir2 psftp gt get filename ext dirl dir2filename ext no such file or directory This is not a bug in PSFTP There is a known bug in some versions of portable OpenSSH bug 697 that causes these symptoms it appears to have been introduced around 3 7 x It manifests only on certain platforms AIX is what has been reported to us There is a patch for OpenSSH attached to that bug it s also fixed in recent versions of portable OpenSSH from around 3 8 Do you want to hear about Software caused connection abort http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 110 of 131 In the documentation for PuTTY 0 53 and 0 53b we mentioned that we d like to hear about any occurrences of this error Since the release of PuTTY 0 54 however we ve been convinced that this error doesn t indicate that PuTTY s doing anything wrong and we don t need to hear about further occurrences S section 10 14 for our current documentation of this error A 7 23 My SSH 2 session locks up for a few seconds every so often Recent versio
23. and expects the client to construct them in the same wrong way PuTTY constructs the MACs correctly by default and hence these old servers will fail to work with it If you are using PuTTY version 0 52 or better this should work automatically PuTTY should detect the buggy servers from their version number announcement and automatically start to construct its MACs in the same incorrect manner as they do so it will be able to work with them If you are using PuTTY version 0 51 or below you can enable the workaround by going to the SSH panel and ticking the box labelled Imitate SSH2 MAC bug It s possible that you might have to do this with 0 52 as well if a buggy server exists that PuTTY doesn t know about In this context MAC stands for Message Authentication Code It s a cryptographic term and it has nothing at all to do with Ethernet http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 ala oT a bes ai ie Page 104 of 131 MAC Media Access Control addresses Why do I see Fatal Protocol error Expected control record in PSCP This happens because PSCP was expecting to see data from the server that was part of the PSCP protocol exchange and instead it saw data that it couldn t make any sense of at all This almost always happens because the startup scripts in your account on the server machine are generating output This is impossible for PSCP or any other SCP
24. either by copying it out of the key for pasting into authorized_keys file or by using the Save public key button public key to your server generated th key section 8 2 7 you don t need to do this private key back into immediately PuTTYgen later s to actually generat select a comm See section 8 2 8 box section 8 2 9 if you want section 8 2 11 Page 81 of 131 the key nt field section press the You may also want to copy the Public see section 8 2 10 However you can load the and the public key will be available for copying and pasting again Section 8 3 describes attempt public key authentication to accept it Selecting the type of key Before generating a key pair using PuTTYgen which type of key you need of key An RSA key for use with An RSA key for use with A DSA key for use with t The SSH 1 protocol only supports you must key will be completely useless using the SSH 1 protocol of future sessions precautions to avoid this weakness have managed it using RSA keys instead he SSH 2 protocol supports more supported by PuTTY are RSA and DSA he SSH 2 protocol RSA keys than on the SSH 1 protocol the SSH 2 protocol the typical process of configuring PuTTY to and configuring your SSH server you need to select PuTTYgen currently supports three types if you will be conne
25. environment variable type into the console window set PATH C path to putty directory sPATHS This will only work for the lifetime of that particular console window To set your PATH more permanently on Windows NT 2000 and XP use the Environment tab of the System Control Panel On Windows 95 98 and ME you will need to edit your AUTOEXEC BAT to include a set command like the one abov 7 2 Using Plink This section describes the basics of how to use Plink for interactive logins and for automated processes Once you ve got a console window to type into you can just type plink on its own to bring up a usage message This tells you the version of Plink you re using and gives you a brief summary of how to use Plink Z sysosd gt plink PuTTY Link command line connection utility Release 0 60 Usage plink options user host command host can also be a PuTTY saved session name Options V print version information and exit http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 76 of 131 pgpfp print PGP key fingerprints and exit v show verbose messages load sessname Load settings from saved session ssh telnet rlogin raw force use of a particular protocol P port connect to specified port 1 user connect with specified usernam batch disable all interactive prompts The following options only apply to SSH connections pw passw login with specifie
26. is a much simpler protocol A 7 8 When I run full colour applications I see areas of black space where colour ought to be or vice versa You almost certainly need to change the Use background colour to rase screen setting in the Terminal panel If there is too much black space the commoner situation you should enable it while if there is too much colour you should disable it See section 4 3 4 In old versions of PuTTY this was disabled by default and would not take effect until you reset the terminal see question A 7 9 Since 0 54 it is enabled by default and changes take effect immediately A 7 9 When I change some terminal settings nothing happens Some of the terminal options notably Auto Wrap and background colour screen erase actually represent the _default_ setting rather than the currently active setting The server can send sequences that modify these options in mid session but when the terminal is reset by server action or by you choosing Reset Terminal from the System menu the defaults are restored In versions 0 53b and prior if you change one of these options in the middle of a session you will find that the change does not immediately take effect It will only take effect once you reset the http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 A 7 10 A 7 11 A 7 12 Page 106 of 131 terminal In version 0 54 the behaviour has changed
27. locks might plausibly be willing to accept financial liability for a product that failed to perform as advertised and resulted in damage e g valuables being stolen The reason they can afford to do this is because they sell a _lot_ of units and only a small proportion of them will fail so they can meet their financial liability out of the income from all the rest of their sales and still have enough left over to make a profit Financial liability is intrinsically linked to selling your product for money There are two reasons why PuTTY is not analogous to a physical lock in this context One is that software products don t exhibit random variation _if_ PuTTY has a security hole which does happen although we do our utmost to prevent it and to respond quickly when it does every copy of PuTTY will have the same hole so it s likely to affect all the users at the same time So even if our users were all paying us to use PuTTY we wouldn t be able to _simultaneously_ pay every affected user compensation in excess of the amount they had paid us in the first place It just wouldn t work The second much more important reason is that PuTTY users _don t_ pay us The PuTTY team does not have an income it s a volunteer effort composed of people spending their spare time to try to write useful software We aren t even a company or any kind of legally recognised organisation We re just a bunch of peopl
28. sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 41 of 131 protocols offer no way of implementing them For an alternative see section 4 13 3 Note that if you are using SSH 1 and the server has a bug that makes it unable to deal with SSH 1 ignore messages s section 4 24 1 enabling keepalives will have no effect 4 13 2 Disable Nagle s algorithm Nagle s algorithm is a detail of TCP IP implementations that tries to minimise the number of small data packets sent down a network connection With Nagle s algorithm enabled PuTTY s bandwidth usage will be slightly more efficient with it disabled you may find you get a faster response to your keystrokes when connecting to some types of server H he Nagle algorithm is disabled by default for interactive connections 4 13 3 Enable TCP keepalives _NOTE _ TCP keepalives should not be confused with the application level keepalives described in section 4 13 1 If in doubt you probably want application level keepalives TCP keepalives ar provided for completeness The idea of TCP keepalives is similar to application level keepalives and the same caveats apply The main differences are TCP keepalives are available on _all_ connection types including Raw and Rlogin The interval between TCP keepalives is usually much longer typically two hours this is set by the operating system and cann
29. the small size and the ease code contributions that hat add a huge amount to the So or t S hich is only useful to a small minority of t immediately a DLL plugin interface for PuTTY tures can be implemented in plugin is that those DLLs will be hem on startup it should run won t provide those particular features one day contain ten or twenty h would cut down a little on the ease of needed ease of installation you or just the DLLs till work fine Depending on _external_ at all possible authentication mechanisms avoided the important t graceful degradation it may DLLs is something we d like to avoid if though for some purposes such as complex SSH be unavoidable If it can t be hing is to follow the same principle of if a DLL can t be found then PuTTY should run happily and just not supply the feature that depended on it Single threaded cod PuTTY and its supporting tools them run in only one OS thread This mea there s two threads at once by recursion The only way or at least the vast majority of ns that if you re devising some piece of internal mechanism no need to use locks to make sure it doesn t get called by called r code can b ntrantly is That said most of Windows PuTTY s network handling is triggered off Windows messages requested by MessageBox deep within some network event WSAAsyncSelect so if you call handl
30. 1 Controlling the appearance of the cursor The Cursor appearance option lets you configure the cursor to be a block an underline or a vertical line A block cursor becomes an empty box when the window loses focus an underline or a vertical line becomes dotted The Cursor blinks option makes the cursor blink on and off This works in any of the cursor modes 4 8 2 Controlling the font used in the terminal window This option allows you to choose what font in what size the PuTTY terminal window uses to display the text in the session You will be offered a choice from all the fixed width fonts installed on the system VT100 style terminal handling can only deal with fixed width fonts 4 8 3 Hide mouse pointer when typing in window If you enable this option the mouse pointer will disappear if the PuTTY window is selected and you press a key This way it will not obscure any of the text in the window while you work in your session As soon as you move the mouse the pointer will reappear This option is disabled by default so the mouse pointer remains visible at all times 4 8 4 Controlling the window border PuTTY allows you to configure the appearance of the window border to some extent The checkbox marked Sunken edge border changes the appearance of the window border to something more like a DOS box the inside edge of the border is highlighted as if it sank down to meet
31. 2 public key authentication will fail This is an SSH 2 specific bug 4 24 8 Handles SSH 2 key r xchange badly Some SSH servers cannot cope with repeat key exchange at all and will ignore attempts by the client to start one Since PuTTY pauses the session while performing a repeat key exchange the effect of this would be to cause the session to hang after an hour unless you have your rekey timeout set differently see section 4 19 2 for more about rekeys Other very old SSH servers handle repeat key exchange even more badly and disconnect upon receiving a repeat key exchange request If this bug is detected PuTTY will never initiate a repeat key exchange If this bug is enabled when talking to a correct server the session should still function but may be less secure than you would expect his is an SSH 2 specific bug 4 25 The Serial panel he Serial panel allows you to configure options that only apply when PuTTY is connecting to a local serial line 4 25 1 Selecting a serial line to connect to The Serial line to connect to box allows you to choose which serial line you want PuTTY to talk to if your computer has more than one serial port On Windows the first serial line is called COM1 and if there is a second it is called COM2 and so on This configuration setting is also visible on the Session panel where it replaces the Host Name box see s
32. 2 specific bug 4 24 6 Requires padding on SSH 2 RSA signatures Versions below 3 3 of OpenSSH require SSH 2 RSA signatures to be padded with zero bytes to the same length as the RSA key modulus The SSH 2 specification says that an unpadded signature MUST be accepted so this is a bug A typical symptom of this problem is that PuTTY mysteriously fails RSA authentication once in every few hundred attempts and falls back to passwords If this bug is detected PuTTY will pad its signatures in the way OpenSSH expects If this bug is enabled when talking to a correct server it is likely that no damage will be done since correct servers usually still accept padded signatures because they re used to talking to OpenSSH This is an SSH 2 specific bug http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 59 of 131 4 24 7 Misuses the session ID in SSH 2 PK auth Versions below 2 3 of OpenSSH require SSH 2 public key authentication to be done slightly differently the data to be signed by the client contains the session ID formatted in a different way If public key authentication mysteriously does not work but the Event Log see section 3 1 3 1 thinks it has successfully sent a signature it might be worth enabling the workaround for this bug to see if it helps If this bug is detected PuTTY will sign data in the way OpenSSH expects If this bug is enabled when talking to a correct server SSH
33. 3 4 16 4 http the earth li sgtatham putty 0 60 puttydoc txt implementations ou 1 Therefore it s po 1 one PuTTY clai lt q he problem wa new Telnet mec like the origi implementation unambiguous T passing enviro Passive and ac t there This switch allows you to choose which ms to be s solved by issuing a second standard defining a hanism called NEW_ENVIRON which behaved exactly nal OLD_ENVIRON but was not encumbered by existing s Most Telnet servers now support this and it s his feature should only be needed if you have trouble nment variables to quite an old server tive Telnet negotiation modes In a Telnet connection there are two types of data passed between the client and the server actual text and _negotiations_ about which Telnet extra features to use PuTTY can use two different strategies for negotiation In _active_ mode PuTTY starts to send negotiatio the connection is opened NS aS Soon as In _passive_ mode PuTTY will wait to negotiate until it sees a negotiation from the server he server is then negotiation will never begin The obvious disadvantage of passive mode is that if t also operating in a passive mode at all For this reason PuTTY defaults to active mode However sometimes passive mode is required in order to successfully get through certain types of firewall and Telnet proxy server If you have confusi
34. ANSI printer output to drop down list box This should allow you to select from all the printers you have installed drivers for on your computer Alternatively you can type the network name of a networked printer for example printserver printerl even if you haven t already installed a driver for it on your own machine When the remote server attempts to print some data PuTTY will send that data to the printer _raw_ without translating it attempting K to format it or doing anything else to it It is up to you to ensure your remote server knows what type of printer it is talking to Since PuTTY sends data to the printer raw it cannot offer options such as portrait versus landscape print quality or paper tray selection All these things would be done by your PC printer driver which PuTTY bypasses if you need them done you will have to find a way to configure your remote server to do them To disable remote printing again choose None printing disabled from the printer selection list This is the default state 4 4 The Keyboard panel The Keyboard configuration panel allows you to control the behaviour of the keyboard in PuTTY The correct state for many of these settings depends on what the server to which PuTTY is connecting expects With a Unix server this is likely to depend on the termcap or terminfo entry it uses which in turn is likely to be control
35. BAD WH T Cc Cc P The Logging configuration panel allows you to save log files of your PuTTY sessions for debugging analysis or future reference The main option is a radio button set that specifies whether PuTTY ill log anything at all The options are None This is the default option in this mode PuTTY will not create a log file at all Printable output In this mode a log file will be created and written to but only printable text will be saved into it The various terminal control codes that are typically sent down an interactive session alongside the printable text will be omitted This might be a useful mode if you want to read a log file in a text editor and hope to be able to make sense of it All session output In this mode _everything_ sent by the server into your terminal session is logged If you view the log file in a text editor therefore you may well find it full of strange control characters This is a particularly useful mode if you are experiencing problems with PuTTY s terminal handling you can record everything that went to the terminal so that someone else can replay the session later in slow motion and watch to see what went wrong SSH packets In this mode which is only used by SSH connections the SSH message packets sent over th ncrypted connection are written to the log file as well as Event Log entries You might ne
36. DES 168 bit SDCTR SSH 2 only or CBC Single DES 56 bit CBC see below for SSH 2 If the algorithm PuTTY finds is below the warn below here line you will see a warning box when you make the connection The first cipher supported by the server is single DES which is below the configured warning threshold Do you want to continue with this connection This warns you that the first available encryption is not a very http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 49 of 131 secure one Typically you would put the warn below here lin between the encryptions you consider secure and the ones you consider substandard By default PuTTY supplies a preference order intended to reflect a reasonable preference in terms of security and speed In SSH 2 the encryption algorithm is negotiated independently for each direction of the connection although PuTTY does not support separate configuration of the preference orders As a result you may get two warnings similar to the one above possibly with different encryptions Single DES is not recommended in the SSH 2 protocol standards but one or two server implementations do support it PuTTY can use single DES to interoperate with these servers if you enable the Enable legacy use of single DES in SSH 2 option by default this is disabled and PuTTY will stick to recommended ciphers 4 19 T
37. Newer SSH 2 servers are more likely to support it than older ones This configuration data is not used in the SSH 1 rlogin or raw protocols To add an environment variable to the list transmitted down the connection you enter the variable name in the Variable box enter its value in the Value box and press the Add button To remove one from the list select it in the list box and press Remove 4 15 The Proxy panel he Proxy panel allows you to configure PuTTY to use various types of proxy in order to make its network connections The settings in this panel affect the primary network connection forming your PuTTY session and also any extra connections made as a result of SSH port forwarding see section 3 5 4 15 1 Setting the proxy type The Proxy type radio buttons allow you to configure what type of proxy you want PuTTY to use for its network connections The default setting is None in this mode no proxy is used for any connection Selecting HTTP allows you to proxy your connections through a web server supporting the HTTP CONNECT command as documented in RFC 2817 Selecting SOCKS 4 or SOCKS 5 allows you to proxy your connections through a SOCKS server Many firewalls implement a less formal type of proxy in which a user can make a Telnet connection directly to the firewall machine and enter a command such as connect myhost com 22 to connect through to an external host Se
38. Page 116 of 131 time money or effort to deal with US bureaucracy to investigate any further We believe that PuTTY falls under 5D002 on the US Commerce Control List but that shouldn t be taken as definitive If you need to know more you should seek professional legal advice The same applies to any other country s legal requirements and restrictions Similarly some people have asked us for FIPS certification of the PuTTY tools Unless someone else is prepared to do the necessary work and pay any costs we can t provide this Miscellaneous questions Is PuTTY a port of OpenSSH or based on OpenSSH No it isn t PuTTY is almost completely composed of code written from scratch for PuTTY The only code we share with OpenSSH is the detector for SSH 1 CRC compensation attacks written by CORE SDI S A Where can I buy silly putty You re looking at the wrong web site the only PuTTY we know about here is the name of a computer program If you want the kind of putty you can buy as an executive toy the PuTTY team can personally recommend Thinking Putty which you can buy from Crazy Aaron s Putty World at www puttyworld com What does PuTTY mean It s the name of a popular SSH and Telnet client Any other meaning is in the eye of the beholder It s been rumoured that PuTTY is the antonym of getty or that it s the stuff that makes your Windows useful or that it s a kind of plutonium Teletype W
39. PuTTY source in such a way that it will run under Win32s an extension to Windows 3 1 to let you run 32 bit programs In order to do this you ll need the right kind of C compiler modern versions of Visual C at least have stopped being backwards compatible to Win32s Also the last time we tried this it didn t work very well If you re interested in running PuTTY under Windows 3 1 help and testing in this area would be very welcome A 3 6 Will there be a port to the Mac There are several answers to this question The Unix Gtk port is already fully working under Mac OS X as an X11 application A native Cocoa Mac OS X port has been started It s just about usable but is of nowhere near release quality yet and is likely to behave in unexpected ways Currently it s unlikely to be completed unless someone steps in to help A separate port to the classic Mac OS pre OSX is also in progress it too is not ready yet A 3 7 Will there be a port to EPOC I hope so but given that ports aren t really progressing very fast even on systems the developers _do_ already know how to program for it might be a long time before any of us get round to learning a new system and doing the port for that http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 4 wn SD Page 100 of 131 However some of the work has been done by other people and a beta port of PuTTY for the Nokia 9200 Co
40. SSH 1 connections always require an authentication step 4 20 2 Attempt authentication using Pageant If this option is enabled then PuTTY will look for Pageant the SSH private key storage agent and attempt to authenticate with any suitable public keys Pageant currently holds This behaviour is almost always desirable and is therefor nabled by default In rare cases you might need to turn it off in order to force authentication by some non public key method such as passwords This option can also be controlled using the noagent command line option See section 3 8 3 9 See chapter 9 for more information about Pageant in general 4 20 3 Attempt TIS or CryptoCard authentication TIS and CryptoCard authentication are despite their names generic forms of simple challenge response authentication available in SSH protocol version 1 only You might use them if you were using S Key one time passwords for example or if you had a physical security token that generated responses to authentication challenges With this switch enabled PuTTY will attempt these forms of authentication if the server is willing to try them You will be presented with a challenge string which will be different every time and must supply the correct response in order to log in If your server supports this you should talk to your system administrator about precisely what form these challenges and responses tak
41. See section 3 5 for a general d how it works Tunnels panel shows a list of all try to set up when it connects so this radio buttons depending on whether you want to forward a local port to a remote destination C Local C Remote Alternatively provide a local SOCKS 4 4A 5 this proxy only supports TCP not support forwarding UDP orwardings emote forwardings he remote machine listen on port your SSH Note f r t If you have selected Local needed with Dynamic ente separated by a colon in the received on t or forward a remote port to a select Enter a source port number into t PuTTY will listen on that mos numbers less than local destination Dynamic if you want PuTTY to proxy on a local port note that connections the SSH protocol does he Source port box For local this port of your PC For server will listen on this port of servers will not allow you to 1024 or Remote this step is not r a hostname and port number Destination box Connections he source port will be directed to this destination For example to connect to a POP 3 server you might enter popserver example com 110 Click the Add button Your forwarding details should appear in the list box To remove a port forwarding simply selec its details in the list box and click the Remove In the Source port address to listen on See section 3 5 for more informa
42. Special commands Depending on the protocol used for the current session there may be a submenu of special commands These are protocol specific tokens such as a break signal that can be sent down a connection in addition to normal data Their precis ffect is usually up to the server Currently only Telnet SSH and serial connections have special commands The break signal can also be invoked from the keyboard with Ctrl Break m q he following special commands are available in Telnet Are You There Break http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Synch Erase PuTTY is pr Page 7 of 131 Character can also be configured to send this when the Backspace key ssed s section 4 16 3 as Erase Line Go Ahead No Operation Should have no effect Abort Abort Process Output Interrupt Process PUTTY can also be configured to send this when Ctrl C is typed see section 4 16 3 Suspend Process PuTTY can also be configured to send this when Ctrl Z is typed see section 4 16 3 End Of Record End Of File In an SSH IGNOR connection the following special commands are available E message Should have no effect Repeat key exchange Only available in SSH 2 Forces a repeat key exchange immediately and resets associated timers and counters For more information abou
43. a username to log in as see section 4 14 1 http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 66 of 131 In PSCP you can now use the name of the session instead of a hostname type pscp sessionname file localfile where sessionname is replaced by the name of your saved session Secondly you can supply the name of a private key file on the command line with the i option See section 3 8 3 18 for more information Thirdly PSCP will attempt to authenticate using Pageant if Pageant is running see chapter 9 So you would do this Ensure Pageant is running and has your private key stored in it Specify a user and host name to PSCP as normal PSCP will automatically detect Pageant and try to use the keys within it For more general information on public key authentication see chapter 8 Chapter 6 Using PSFTP to transfer files securely PSFTP the PuTTY SFTP client is a tool for transferring files securely between computers using an SSH connection PSFTP differs from PSCP in the following ways PSCP should work on virtually every SSH server PSFTP uses the new SFTP protocol which is a feature of SSH 2 only PSCP will also use this protocol if it can but there is an SSH 1 equivalent it can fall back to if it cannot PSFTP allows you to run an interactive file transfer session much like the Windows ftp program You can list the contents of
44. accept them In particular OpenSSH does not accept a change of username once you have sent one username it will reject attempts to try to authenticate as another user Depending on the version of OpenSSH it may quietly return failure for all login attempts or it may send an error message For this reason PuTTY will by default not prompt you for your username more than once in case the server complains If you know your server can cope with it you can enable the Allow attempted changes of username option to modify PuTTY s behaviour 4 20 7 Private key file for authentication This box is where you enter the name of your private key file if you are using public key authentication See chapter 8 for information about public key authentication in SSH This key must be in PuTTY s native format PPK If you have a private key in another format that you want to use with PuTTY see section 8 2 12 If a key file is specified here and Pageant is running see chapter 9 PuTTY will first try asking Pageant to authenticate with that key and ignore any other keys Pageant may have If that fails PuTTY will ask for a passphrase as normal 4 21 The Y panel he Y panel lets you configure the remote pseudo terminal 4 21 1 Don t allocate a pseudo terminal When connecting to a Unix system most interactive shell sessions are run in a _pseudo terminal_ which allows the Uni
45. allowing wildcards For example example com This excludes any host with a name ending in example com from proxying 192 168 88 This excludes any host with an IP address starting with 192 168 88 from proxying 192 168 88 example com This excludes both of the above ranges at once Connections to the local host the host name localhost and any loopback IP address are never proxied even if the proxy exclude list does not explicitly contain them It is very unlikely that this behaviour would ever cause problems but if it does you can change it by enabling Consider proxying local host connections Note that if you are doing DNS at the proxy see section 4 15 3 you should make sure that your proxy exclusion settings do not depend on knowing the IP address of a host If the name is passed on to the proxy without PuTTY looking it up it will never know the IP address and cannot check it against your list 4 15 3 Name resolution when using a proxy If you are using a proxy to access a private network it can make a difference whether DNS name resolution is performed by PuTTY itself on the client machine or performed by the proxy The Do DNS name lookup at proxy end configuration option allows you to control this If you set it to No PuTTY will always do its own DNS and will always pass an IP address to the proxy If you set it to Yes PuTTY will always pass host names straight to th
46. an automated password free form of login by means of a file called rhosts on the server You put a line in your rhosts file saying something like jbloggs pcl example com and then when you make an Rlogin connection the client transmits the username of the user running the Rlogin client The server checks the username and hostname against rhosts and if they match it d oes not ask for a password This only works because Unix systems contain a safeguard to stop a user from pretending to be another user in an Rlogin connection Rlogin connections have to come from port numbers below 1024 and Unix systems prohibit this to unprivileged processes so when the server sees a connection from a low numbered port it assumes the client end of the connection is held by a privileged and therefore trusted process so it believes the claim of who the user is Windows does not have this restriction _any_ user can initiate an outgoing connection from a low numbered port Hence the Rlogin rhosts mechanism is completely useless for securely distinguishing several different users on a Windows machine If you have a rhosts entry pointing at a Windows PC you should assume that _anyone_ using that PC can spoof your username in an Rlogin connection and access your account on the server The Local username control allows you to specify what user name PuTTY should claim you have in case it doesn t match your Win
47. an official Windows DLL as part of the Windows API is fine and anything defined in the C library standard is also fine because those should be available irrespective of compilation environment But things in between available as non standard library and language extensions in only one compiler are disallowed _snprintf in particular should be unnecessary since we provide dupprintf see section D 5 Compiler independence should apply on all platforms of course not just on Windows http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 D 7 Small code size PuTTY is tiny it s easy to install compared to many other Windows applications it depends on no D no service packs or system upgrades install that executable wherever you wan Page 126 of 131 And LLs no other applications It s just one executable You t to and run it We want to keep both thes depend critically on external DLL code size for a feature w users are likely to be thrown ou We do vaguely intend to introduce whereby seriously large extra fea modules The important thing _optional_ if PuTTY can find t perfectly happily and jus A full installation of PuTTY migh little DLL plugins whic installation but if you really _could_ still just you really needed would s eis and properties of installation if at all possible though install the one PuTTY binary
48. around the session name if it contains spaces If you want to create a Windows shortcut to start a PuTTY saved session this is the option you should use your shortcut should call something like d path to putty exe load my session Note that PuTTY itself supports an alternative form of this option for backwards compatibility If you execute putty sessionname it will have the sam ffect as putty load sessionname With the form no double quotes are required and the sign must be the very first thing on the command line This form of the option is deprecated 3 8 3 2 Selecting a protocol ssh telnet rlogin raw To choose which protocol you want to connect with you can use one of these options ssh selects the SSH protocol telnet selects the Telnet protocol rlogin selects the Rlogin protocol raw selects the raw protocol These options are not available in the file transfer tools PSCP and http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 14 of 131 PSFTP which only work with the SSH protocol These options are equivalent to the protocol selection buttons in the Session panel of the PuTTY configuration box see section 4 1 1 3 8 3 3 v increase verbosity Most of the PuTTY tools can be made to tell you more about what they are doing by supplying the v option If you are having trouble when making a connecti
49. as appendix A in the manual and see if it answers your question The FAQ lists the most common things which people think are bugs but which aren t bugs Download the latest development snapshot and see if the problem still happens with that This really is worth doing As a general rule we aren t very interested in bugs that appear in the release version but not in the development version because that usually means they are bugs we have _already fixed_ On the other hand if you can find a bug in the development version that doesn t appear in the release that s likely to be a new b ug we ve introduced since the release and we re definitely nterested in it none of those options solved your problem and you still need report a bug to us it is useful if you include some general information Tell us what version of PuTTY you are running To find this out use the About PuTTY option from the System menu Please _do not_ just tell us I m running the latest version e mail can be delayed and it may not be obvious which version was the latest at the time you sent the messag PuTTY is a multi platform application tell us what version of what OS you are running PuTTY on If you re running on Unix or Windows for Alpha tell us or we ll assume you re running on Windows for Intel as this is overwhelmingly the case http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 5 ell
50. by PuTTY Controlling character set translation During an interactive session PuTTY receives a stream of 8 bit bytes from the server and in order to display them on the screen it needs to know what character set to interpret them in There are a lot of character sets to choose from The Received data assumed to be in which character set option lets you select one By default PuTTY will attempt to choose a character set that is right for your locale as reported by Windows if it gets it wrong you can select a different one using this control A few notable character sets are The ISO 8859 series are all standard character sets that include various accented characters appropriate for different sets of languages The Winl25x series are defined by Microsoft for similar purposes In particular Winl252 is almost equivalent to ISO 8859 1 but contains a few extra characters such as matched quotes and the Euro symbol If you want the old IBM PC character set with block graphics and line drawing characters you can select CP437 PuTTY also supports Unicode mode in which the data coming from the server is interpreted as being in the UTF 8 encoding of Unicode If you select UTF 8 as a character set you can use this mode Not all server side applications will support it If you need support for a numeric code page which is not listed in the drop down list such as code page 866 then you c
51. changes to a nonsense string Don t do that then It is designed behaviour that PuTTY should have the ability to adjust the window title on instructions from the server Normally the control sequence that does this should only be sent deliberately by programs that know what they are doing and intend to put meaningful text in the window title Writing a binary file to your terminal runs the risk of sending the same control sequence by accident and cause unexpected changes in the window title Don t do its My keyboard stops working once PuTTY displays the password prompt No it doesn t PuTTY just doesn t display the password you type so that someone looking at your screen can t see what it is Unlike the Windows login prompts PuTTY doesn t display the password as a row of asterisks either This is so that someone looking at your screen can t even tell how _long_ your password is which might be valuable information One or more function keys don t do what I expected in a server side application If you ve already tried all the relevant options in the PuTTY Keyboard panel you may need to mail the PuTTY maintainers and ask It is _not_ usually helpful just to tell us which application which server operating system and which key isn t working in order to replicate the problem we would need to have a copy of every operating system and every application that anyone has ever complained about PuTTY responds
52. clearly marked PSFTP also supports some of its own options The following sections describe PSFTP s specific command line options 6 1 1 b specify a file containing batch commands In normal operation PSFTP is an interactive program which displays a command line and accepts commands from the keyboard If you need to do automated tasks with PSFTP you would probably prefer to specify a set of commands in advance and have them executed automatically The b option allows you to do this You use it with a file name containing batch commands For example you might create a file called myscript scr containing lines like this cd home ftp users jeff del jam old tar gz ren jam tar gz jam old tar gz put jam tar gz chmod atr jam tar gz and then you could run the script by typing psftp user hostname b myscript scr When you run a batch script in this way PSFTP will abort the script if any command fails to complete successfully To change this behaviour you can add the be option section 6 1 3 PSFTP will terminate after it finishes executing the batch script 6 1 2 bc display batch commands as they are run The bc option alters what PSFTP displays while processing a batch script specified with b With the bc option PSFTP will display prompts and commands just as if the commands had been typed at the keyboard So instead of seeing this C gt psftp fred hostname b batchfile Sent userna
53. client to work around You should never use startup files bashrc cshrce and so on which generate output in non interactive sessions This is not actually a PuTTY problem If PSCP fails in this way then all other SCP clients are likely to fail in exactly the same way The problem is at the server end I clicked on a colour in the Colours panel and the colour didn t change in my terminal That isn t how you re supposed to use the Colours panel During the course of a session PuTTY potentially uses _all_ the colours listed in the Colours panel It s not a question of using only one of them and you choosing which one PuTTY will use them _all_ The purpose of the Colours panel is to let you adjust the appearance of all the colours So to change the colour of the cursor for example you would select Cursor Colour press the Modify button and select a new colour from the dialog box that appeared Similarly if you want your session to appear in green you should select Default Foreground and press Modify Clicking on ANSI Green won t turn your session green it will only allow you to adjust the _shade_ of green used when PuTTY is instructed by the server to display green text Plink on Windows 95 says it can t find WS2_32 DLL Plink requires th xtended Windows network library WinSock version 2 This is installed as standard on Windows 98 and above and on Windows
54. close the network connection but keep PSFTP running you can use the close command You can then use the open command to open a new connection 6 2 6 The help command get quick online help If you type help PSFTP will give a short list of the available commands If you type help with a command nam for example help get then PSFTP will give a short piece of help on that particular command 6 2 7 The cd and pwd commands changing the remote working directory PSFTP maintains a notion of your working directory on the server This is the default directory that other commands will operate on For example if you type get filename dat then PSFTP will look for filename dat in your remote working directory on the server To change your remote working directory use the cd command If you don t provide an argument cd will return you to your home directory on the server more precisely the remote directory you were in at the start of the connection To display your current remote working directory type pwd 6 2 8 The lcd and lpwd commands changing the local working directory As well as having a working directory on the remote server PSETP also has a working directory on your local machine just like any other Windows process This is the default local directory that other commands will operate on For example if you type get filename dat then PSFTP wi
55. contracts of employment and are generally not signed except in return for a sizeable salary If we _were_ to stop developing PuTTY or to decide to make all future releases closed source then you would still be free to copy the last open release in accordance with the current licence and in particular you could start your own fork of the project from that release If this happened I confidently predict that _somebody_ would do that and that some kind of a free PuTTY would continue to be developed There s already precedent for that sort of thing happening in free software We can t guarantee that somebody _other than you_ would do it of course you might have to do it yourself But we can assure you that there would be nothing _preventing_ anyone from continuing free development if we stopped Finally we can also confidently predict that if we made PuTTY closed source and someone made an open source fork most people would switch to the latter Therefore it would be pretty stupid of us to try it Can you provide us with export control information FIPS certification for PuTTY Some people have asked us for an Export Control Classification Number ECCN for PuTTY We don t know whether we have one and as a team of free software developers based in the UK we don t have the http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 A 10 1 A 10 2 A 10 3 A 10 4
56. copying _from_ a UNIX system _to_ a Windows system you would use the wildcard syntax allowed by your UNIX shell e g If the source is a remote server and you do not specify a full pathname in UNIX a pathname beginning with a slash character what you specify as a source will be interpreted relative to your home directory on the remote server 5 2 1 4 target The filename or directory to put the file s When copying from a http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 64 of 131 remote server to a local host you may wish simply to place the file s in the current directory To do this you should specify a target of For example pscp fred example com home tom emacs would copy home tom emacs on the remote server to the current directory As with the source parameter if the target is on a remote server and is not a full path name it is interpreted relative to your home directory on the remote server 5 2 2 Options PSCP accepts all the general command line options supported by the PuTTY tools xcept the ones which make no sense in a file transfer utility See section 3 8 3 for a description of these options The ones not supported by PSCP are clearly marked PSCP also supports some of its own options The following sections describe PSCP s specific command line options 5 2 2 1 ls list remote files If the ls option is given no fi
57. down Alt when you make your selection You can also configure rectangular selection to be the default and then holding down Alt gives the normal behaviour instead See section 4 11 4 for details If you have a middle mouse button then you can use it to adjust an existing selection if you selected something slightly wrong If you have configured the middle mouse button to paste then the right mouse button does this instead Click the button on the screen and you can pick up the nearest end of the selection and drag it to somewhere else It s possible for the server to ask to handle mouse clicks in the PuTTY window itself If this happens the mouse pointer will turn into an arrow and using the mouse to copy and paste will only work if you hold down Shift See section 4 6 2 and section 4 11 3 for details of this feature and how to configure it http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 6 of 131 3 1 2 Scrolling the screen back PuTTY keeps track of text that has scrolled up off the top of the terminal So if something appears on the screen that you want to read but it scrolls too fast and it s gone by the time you try to look for it you can use the scrollbar on the right side of the window to look back up the session history and find it again As well as using the scrollbar you can also page the scrollback up and down by pressing Shift PgUp and Shift PgDn You can scroll a line at a time us
58. is under way Currently PuTTY does _not_ run on Windows CE see question A 3 4 and it does not quite run on the Win32s environment under Windows 3 1 see question A 3 5 We do not have release quality ports for any other systems at the present time If anyone told you we had an EPOC port or an iPaq port or any other port of PuTTY they were mistaken We don t There are some third party ports to various platforms mentioned on the Links page of our website Is there a port to Unix As of 0 54 there are Unix ports of most of the traditional PuTTY tools and also on ntirely new application If you look at the source release you should find a unix subdirectory containing Makefile gtk which should build you Unix ports of Plink PuTTY itself PuTTYgen PSCP PSFTP and also pterm an xterm type program which supports the same terminal emulation as PuTTY We do not yet have a Unix port of Pageant If you don t have Gtk you should still be able to build the command line tools Note that Unix PuTTY has mostly only been tested on Linux so far portability problems such as BSD style ptys or different header fil requirements are expected What s the point of the Unix port Unix has OpenSSH All sorts of little things pterm is directly useful to anyone who prefers PuTTY s terminal emulation to xterm s which at least some http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page
59. keys and Home End etc http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 27 of 131 In application mode all the keypad keys send special control sequences _including_ Num Lock Num Lock stops behaving like Num Lock and becomes another function key Depending on which version of Windows you run you may find the Num Lock light still flashes on and off every time you press Num Lock even when application mode is active and Num Lock is acting like a function key This is unavoidable Application keypad mode can be turned on and off by the server depending on the application PuTTY allows you to configure the initial state You can also disable application keypad mode completely using the Features configuration panel see section 4 6 1 4 4 6 Using NetHack keypad mode PuTTY has a special mode for playing NetHack You can enable it by selecting NetHack in the Initial state of numeric keypad control In this mode the numeric keypad keys 1 9 generate the NetHack movement commands hjklyubn The 5 key generates the command do nothing In addition pressing Shift or Ctrl with the keypad keys generate the Shift or Ctrl keys you would expect e g keypad 7 generates y so Shift keypad 7 generates Y and Ctrl keypad 7 generates Ctrl Y these commands tell NetHack to keep moving you in the same direction until you encounter something interesting For some
60. mail on Unix machines so copying the file to a Windows box to run Word is very inconvenient Not only that but several of us don t even _have_ a copy of Word Some people like to send us screen shots when demonstrating a problem Please don t do this without checking with us first we almost never actually need the information in the screen shot Sending a screen shot of an error box is almost certainly unnecessary when you could just tell us in plain text what the error was On some versions of Windows pressing Ctrl C when the error box is displayed will copy the text of the message to the clipboard Sending a full screen shot is _occasionally_ useful but it s probably still wise to check whether we need it before sending iE If you _must_ mail a screen shot don t send it as a BMP file BMPs have no compression and they are _much_ larger than other image formats such as PNG TIFF and GIF Convert the file to a properly compressed image format before sending it Please don t mail us executables at all Our mail server blocks all incoming e mail containing executables as a defence against the vast numbers of e mail viruses we receiv very day If you mail us an executable it will just bounce If you have made a tiny modification to the PuTTY code please send us a _patch_ to the source code if possible rather than sending us a huge ZIP file containing the complete sources plus your modification If
61. mirroring then you might want to mail us before setting up the mirror see also the guidelines on the Mirrors page but if you just want to ask for permission you don t need to You already have permission B 9 Praise and compliments is getting e mails that just say thanks We are always happy to receive e mails of this type One of the most rewarding things about maintaining free software Regrettably we don t have time to answer them all in person If you mail us a compliment and don t receive a reply _please_ don t think we ve ignored you We did receive it and we were happy about it we just didn t have time to tell you so personally cv aA To everyone who s ever sent us praise and compliments in the past and the future _you re welcome_ B 10 E mail address The actual address to mail is lt putty projects tartarus org gt Appendix C PuTTY Licence http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 123 of 131 PuTTY is copyright 1997 2007 Simon Tatham Portions copyright Robert de Bath Joris van Rantwijk Delian Delchev Andreas Schultz Jeroen Massar Wez Furlong Nicolas Barry Justin Bradford Ben Harris Malcolm Smith Ahmad Khalifa Markus Kuhn and CORE SDI S A Permission is hereby granted free of charge to any person obtaining a copy of this software and associated documentation files the Software to deal in the Software without restriction includ
62. one of the persistent state structures either the local state structures s or st in each function or the backend wid structure ssh See http www chiark greenend org uk sgtatham coroutines html for a more in depth discussion of what these macros are for and how they work Single compilation of each source file The PuTTY build system for any given platform works on the following very simple model Each source file is compiled precisely once to produce a single object file Each binary is created by linking together some combination of those object files Therefore if you need to introduce functionality to a particular module which is only available in some of the tool binaries for example a cryptographic proxy authentication mechanism which needs to be left out of PuTTYtel to maintain its usability in crypto hostile jurisdictions the _wrong_ way to do it is by adding ifdefs in say proxy c This would require separate compilation of proxy c for PuTTY and PuTTYtel which means that the entire Makefile generation architecture s section D 11 would have to be significantly redesigned Unless you are prepared to do that redesign yourself _and_ guarantee that it will still port to any future platforms we might decide to run on you should not attempt this The _right_ way to introduce a feature like this is to put the new code in a separate source file and i
63. panel and enter the directly reachable proxy host name on the Proxy panel This feature is only available in SSH protocol version 2 since the version 1 protocol assumes you will always want to run a shell It is not available in the file transfer tools PSCP and PSFTP It is available in PuTTY itself although it is unlikely to be very useful in any tool other than Plink Also nc uses the same server functionality as port forwarding so it will not work if your server administrator has disabled port forwarding The option is named nc after the Unix program nc short for netcat The command plink host1 nc host2 port is very similar in functionality to plink hostl nc host2 port which invokes nc on the server and tells it to connect to the specified destination However Plink s built in nc option does not depend on the nc program being installed on the server 3 8 3 15 C enable compression The C option enables compression of the data sent across the network This option is only meaningful if you are using SSH This option is equivalent to the Enable compression checkbox in the SSH panel of the PuTTY configuration box see section 4 18 3 3 8 3 16 1 and 2 specify an SSH protocol version The 1 and 2 options force PuTTY to use version 1 or version 2 of the SSH protocol These options are only meaningful if you are using SSH These opt
64. panel of the PuTTY configuration box see section 4 1 1 3 8 3 8 pw specify a password A simple way to automate a remote login is to supply your password on the command line This is _not recommended_ for reasons of security If you possibly can we recommend you set up public key authentication instead See chapter 8 for details Note that the pw option only works when you are using the SSH protocol Due to fundamental limitations of Telnet and Rlogin these protocols do not support automated password authentication 3 8 3 9 agent and noagent control use of Pageant for authentication The agent option turns on SSH authentication using Pageant and noagent turns it off These options are only meaningful if you are using SSH See chapter 9 for general information on Pageant These options are equivalent to the agent authentication checkbox in the Auth panel of the PuTTY configuration box see section 4 20 2 3 8 3 10 A and a control agent forwarding The A option turns on SSH agent forwarding and a turns it off These options are only meaningful if you are using SSH See chapter 9 for general information on Pageant and section 9 4 for information on agent forwarding Note that there is a security risk involved with enabling this option see section 9 5 for details These options are equivalent to the agent forwarding checkbox in the Auth panel of the PuTTY configuration box see sect
65. press the Add Key button in the Pageant main window or alternatively right click on the Pageant icon in the system tray and select Add Key from there Pageant will bring up a file dialog labelled Select Private Key File Find your private key file in this dialog and press Open If you want to add more than one key at once you can select multiple files using Shift click to select several adjacent files or Ctrl click to select non adjacent files Pageant will now load the private key s If a key is protected by a passphrase Pageant will ask you to type the passphrase This is not the only way to add a private key to Pageant You can also add one from a remote system by using agent forwarding see section 9 4 for details 9 2 3 The Remove Key button If you need to remove a key from Pageant select that key in the list box and press the Remove Key button Pageant will remove the key from its memory You can apply this to keys you added using the Add Key button or to keys you added remotely using agent forwarding see section 9 4 it makes no difference 9 3 The Pageant command line Pageant can be made to do things automatically when it starts up by specifying instructions on its command line If you re starting Pageant from the Windows GUI you can arrange this by editing the properties of the Windows shortcut that it was started from If Pageant is already runn
66. reason this feature only works properly when Num Lock is on We don t know why ad in a Enabling a DEC like Compose key DEC terminals have a Compose key which provides an easy to remember way of typing accented characters You press Compose and then type two more characters The two characters are combined to produce an accented character The choices of character are designed to be easy to remember for example composing e and produces the e grave character If your keyboard has a Windows Application key it acts as a Compose key in PuTTY Alternatively if you enable the AltGr acts as Compose key option the AltGr key will become a Compose key 4 4 8 Control Alt is different from AltGr Some old keyboards do not have an AltGr key which can make it difficult to type some characters PuTTY can be configured to treat the key combination Ctrl Left Alt the same way as the AltGr key By default this checkbox is checked and the key combination Ctrl Left Alt does something completely different PuTTY s usual handling of the left Alt key is to prefix the Escape Control character to whatever character sequence the rest of the keypress would generate For example Alt A generates Escape followed by a So Alt Ctrl A would generate Escape followed by Control A Ada If you uncheck this box Ctrl Alt will become a synonym for AltGr so you can use it to type extra gr
67. risk In particular try not to use fixed size buffers for variable size data such as strings received from the network or even the user We provide functions such as dupcat and dupprintf which dynamically allocate buffers of the right size for the string they construct Use these wherever possible D 6 Independence of specific compiler Windows PuTTY can currently be compiled with any of four Windows compilers MS Visual C Borland s freely downloadable C compiler the Cygwin mingw32 GNU tools and lcc win32 This is a really useful property of PuTTY because it means peopl who want to contribute to the coding don t depend on having a specific compiler so they don t have to fork out money for MSVC if t i hey don t already have it but on the other hand if they _do_ have t they also don t have to spend effort installing gcc alongside it hey can use whichever compiler they happen to have available or install whichever is cheapest and easiest if they don t have one m herefore we don t want PuTTY to start depending on which compiler you re using Using GNU extensions to the C language for example would ruin this useful property not that anyone s ever tried it and more realistically depending on an MS specific library function supplied by the MSVC C library _snprintf for example is a mistake because that function won t be available under the other compilers Any function supplied in
68. so they will not know what to do with the data PuTTY has provided This authentication mechanism will only work in SSH 2 In SSH 1 the SSH server does not tell the client the source address of a forwarded connection in a machine readable format so it s impossible to verify the XDM AUTHORIZATION 1 data You may find this feature causes problems with some SSH servers which will not clean up XDM AUTHORIZATION 1 data after a http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 session so that if you then connect to a client which only does MIT MAGIC COOKI Page 55 of 131 he same server using 1 and are allocated the same remot authentication data is still connections fail PuTTY s default display number is MIT MAGIC COOKIE 1 EEI T you might find that out of date present on your server and your X If you change it you should be sure you know what you re doing 23 The Tunnels panel he Tunnels panel allows you to connection types through an SSH configure tunnelling of arbitrary connection Port forwarding allows you to tunnel other types of network n SSH session forwarding an connection down a discussion of por The port forwardi the port forwardi to the server list is empty To add a port forwarding Set one of the Local or ng section in the ngs that PuTTY will By default no port forwardings are set up Remote
69. t optimal To connect using SSH 2 to a server that supports both versions you need to change the configuration from the default see question Asul When I m connected to a Red Hat Linux 8 0 system some characters don t display properly A common complaint is that hyphens in man pages show up as a acute With release 8 0 Red Hat appear to have made UTF 8 the default character set There appears to be no way for terminal emulators such as PuTTY to know this as far as we know the appropriate scape sequence to switch into UTF 8 mode isn t sent A fix is to configure sessions to RH8 systems to use UTF 8 translation see section 4 10 1 in the documentation Note that if you use Change Settings changes may not take place immediately see question A 7 9 If you really want to change the character set used by the server the right place is etc sysconfig il8n but this shouldn t be necessary http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 109 of 131 A 7 19 Since I upgraded to PuTTY 0 54 the scrollback has stopped working A 7 20 A 7 21 A 7 22 when I run screen PuTTY s terminal emulator has always had the policy that when the alternate screen is in use nothing is added to the scrollback This is because the usual sorts of programs which use the alternat screen are things like text editors which tend to scroll back and forth in the same documen
70. tell your server that your terminal supports 256 colours On Unix you do this by ensuring that the setting of TERM describes a 256 colour capable terminal You can check this using a command such as infocmp infocmp grep colors colors 256 cols 80 it 8 lines 24 pairs 256 If you do not see colors 256 in the output you may need to change your terminal setting On modern Linux machines you could try xterm 256color 4 12 3 Bolded text is a different colour When the server sends a control sequence indicating that some text should be displayed in bold PuTTY can handle this two ways It can either change the font for a bold version or use the same font ina brighter colour This control lets you choose which By default the box is checked so non bold text is displayed in light grey and bold text is displayed in bright white and similarly in other colours If you uncheck the box bold and non bold text will be displayed in the same colour and instead the font will change to indicate the differenc 4 12 4 Attempt to use logical palettes Logical palettes are a mechanism by which a Windows application running on an 8 bit colour display can select precisely the colours it wants instead of going with the Windows standard defaults If you are not getting the colours you ask for on an 8 bit display you can try enabling this option However be warned that it s never worked very w
71. that also specifies the protocol as SSH Set the Windows environment variable PLINK_PROTOCOL to the word ssh Usually Plink is not invoked directly by a user but run automatically by another process Therefore you typically do not want Plink to prompt you for a user name or a password Next you are likely to need to avoid the various interactive prompts Plink can produce You might be prompted to verify the host key of the server you re connecting to to enter a user name or to enter a password To avoid being prompted for the server host key when using Plink for an automated connection you should first make a _manual_ connection using either of PuTTY or Plink to the same server verify the host key see section 2 2 for more information and select Yes to add the host key to the Registry After that Plink commands connecting to that server should not give a host key prompt unless the host key changes To avoid being prompted for a user name you can Use the 1 option to specify a user name on the command line For example plink login example com 1 fred Set up a PuTTY saved session that describes the server you are connecting to and that also specifies the username to log in as see section 4 14 1 To avoid being prompted for a password you should almost certainly set up public key authentication See chapter 8 for a general introduction to public key authentication Again you
72. the surface inside the window This makes the border a little bit thicker as well It s hard to describe well Try it and see if you like it You can also configure a completely blank gap between the text in the window and the border using the Gap between text and window edge control By default this is set at one pixel You can reduce it to zero or increase it further 4 9 The Behaviour panel The Behaviour configuration panel allows you to control aspects of the behaviour of PuTTY s window 4 9 1 Controlling the window title The Window title edit box allows you to set the title of the PuTTY window By default the window title will contain the host name followed by PuTTY for example serverl example com PUTTY Ny IE you want a different window title this is where to set it PuTTY allows the server to send xterm control sequences which modify the title of the window in mid session unless this is http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 34 of 131 disabled see section 4 6 5 the title string set here is therefore only the _initial_ window title As well as the _window_ title there is also an xterm sequenc to modify the title of the window s _icon_ This makes sense ina windowing system where the window becomes an icon when minimised such as Windows 3 1 or most X Window System setups but in the Windows 95 like user interface it isn t as applicable
73. to recover that data However if you stored an unencrypted key in a disk file they would _certainly_ be able to recover it Although like most modern operating systems Windows prevents programs from accidentally accessing one another s memory space it does allow programs to access one another s memory space deliberately for special purposes such as debugging This means that if you allow a virus trojan or other malicious program on to your Windows system while Pageant is running it could access the memory of the Pageant process extract your decrypted authentication keys and send them back to its master Similarly use of agent _forwarding_ is a security improvement on other methods of one touch authentication but not perfect Holding your keys in Pageant on your Windows box has a security advantage over holding them on the remote server machine itself either in an agent or just unencrypted on disk because if the server machine ever sees your unencrypted private key then the sysadmin or anyone who cracks the machine can steal the keys and pretend to be you for as long as they want http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Chapter 10 However the sysadmin of be you _on that machine_ machine agent connection and request signatures from your private keys They can only do this agent forwarding disappears they lose the ability but using Pageant doesn t actually _preven
74. us what protocol you are Rlogin or Raw mode Page 119 of 131 connecting with SSH Telnet ell us what kind of server you are connecting to what OS and if possible what SSH server if you re using SSH You can get some of this information from 3 1 3 1 in the manual Send us the contents of the P specific reason not to for e problem without needing to kn the PuTTY Event Log see section uTTY Event Log unless you have a xample if it contains confidential information that you think we should be able to solve your Ow Try to give us as much information as you can to help us see the problem for ourselves If possible give us a step by step sequence of _precise_ instructions for reproducing the fault Don t just tell us that PuTTY exactly and precisely what it people tell us PuTTY does the does the wrong thing tell us did and also tell us exactly and precisely what you think it should have done instead Some wrong thing and it turns out that it was doing the right thing and their expectations were wrong telling us exactly what you think Help to avoid this problem by it should have done and exac If you think you can you re problem yourself A patch to excellent addition to a bug r _substitute_ for a good bug r inappropriate and you haven about the actual bug then we solution http www chiark greenend or tly what it di
75. with an Out of memory error This can happen in SSH 2 if PuTTY and the server have not enabled encryption in the same way see question A 7 5 in the FAQ Some http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 92 of 131 versions of OpenSSH have a known problem with this see question Ache Os This can also happen in PSCP or PSFTP if your login scripts on the server generate output the client program will be expecting an SFTP message starting with a length and if it receives some text from your login scripts instead it will try to interpret them as a message length See question A 7 6 for details of this 10 7 Internal error Internal fault Assertion failed Any error beginning with the word Internal should _never_ occur If it does there is a bug in PuTTY by definition please see appendix B and report it to us Similarly any error message starting with Assertion failed is a bug in PuTTY Please report it to us and include the exact text from the error message box 10 8 Unable to use this private key file Couldn t load private key Key is of wrong type Various forms of this error are printed in the PuTTY window or written to the PuTTY Event Log see section 3 1 3 1 when trying public key authentication or given by Pageant when trying to load a private key If you see one of these messages it often indicates th
76. you type any private information such as a password into it However when you connect to a server you have not connected to http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 4 of 131 before PuTTY has no way of telling whether the host key is the right one or not So it gives the warning shown above and asks you whether you want to trust this host key or not Whether or not to trust the host key is your choice If you are connecting within a company network you might feel that all the network users are on the same side and spoofing attacks are unlikely so you might choose to trust the key without checking i I b t If you are connecting across a hostile network such as the nternet you should check with your system administrator perhaps y telephone or in person Some modern servers have more than one host key If the system administrator sends you more than one fingerprint you should make sure the one PuTTY shows you is on the list but it doesn t matter which one it is 2 3 Logging in After you have connected and perhaps verified the server s host key you will be asked to log in probably using a username and a password Your system administrator should have provided you with these Enter the username and the password and the server should grant you access and begin your session If you have mistyped your password most servers will give you several cha
77. 0 seconds 5 minutes in the box Note that keepalives are not always helpful They help if you have a firewall which drops your connection after an idle period but if the network between you and the server suffers from breaks in connectivity then keepalives can actually make things worse If a session is idle and connectivity is temporarily lost between the ndpoints but the connectivity is restored befor ither sid ries to send anything then there will be no problem neither ndpoint will notice that anything was wrong However if one side oes send something during the break it will repeatedly try to e send and eventually give up and abandon the connection Then hen connectivity is restored the other side will find that the irst side doesn t believe there is an open connection any more eepalives can make this sort of problem worse because they increase the probability that PuTTY will attempt to send data during a break in connectivity Other types of periodic network activity can cause this behaviour in particular SSH 2 re keys can have this AhhebaQaodcda ftect S section 4 19 2 Therefore you might find that keepalives help connection loss or you might find they make it worse depending on what _kind_ of network problems you have between you and the server Keepalives are only supported in Telnet and SSH the Rlogin and Raw http the earth li
78. 1 2008 Page 61 of 131 start w putty exe regedit ea new reg HKEY_CURRENT_USER Software SimonTatham PuTTY copy new reg putty reg del new reg regedit s puttydel reg This batch file needs two auxiliary files PUTTYRND REG which sets up an initial safe location for the PUTTY RND random seed file and PUTTYDEL REG which destroys everything in the Registry once it s been successfully saved back to the file Here is PUTTYDEL REG REGI DIT4 AN HKEY_CURRENT_USER Software SimonTatham PuTTY Here is an example PUTTYRND REG file REGEDIT4 HKEY_CURRENT_USER Software SimonTatham PuTTY RandSeedFile a putty rnd You should replace a putty rnd with the location where you want to store your random number data If the aim is to carry around PuTTY and its settings on one floppy you probably want to store it on the floppy Chapter 5 Using PSCP to transfer files securely PSCP the PuTTY Secure Copy client is a tool for transferring files securely between computers using an SSH connection If you have an SSH 2 server you might prefer PSFTP see chapter 6 for interactive use PSFTP does not in general work with SSH 1 servers however Starting PSCP PSCP is a command line application This means that you cannot just double click on its icon to run it and instead you have to bring up a c
79. 2 txt del o Files will be deleted without further prompting even if multiple files are specified del will only delete files You cannot use it to delete directories use rmdir for that The rm command works exactly the same way as del The mkdir command create remote directories To create a directory on the server type mkdir and then the directory name mkdir newstuff You can specify multiple directories to create at once mkdir dirl dir2 dir3 The rmdir command remove remote directories To remove a directory on the server type rmdir and then the directory name or names rmdir oldstuff rmdir old ancient http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 74 of 131 Directories will be deleted without further prompting even if multiple directories are specified Most SFTP servers will probably refuse to remove a directory if the directory has anything in it so you will need to delete the contents first 6 2 18 The mv command move and rename remote files To rename a single file on the server type mv then the current file name and then the new file nam mv oldfile newname You can also move the file into a different directory and change the name mv oldfile dir newname To move one or more files into an existing subdirectory specify the files using wildcards if desired and then the destination directory
80. 99 of 131 people do Unix Plink has apparently found a niche among people who find the complexity of OpenSSL makes OpenSSH hard to install and who don t mind Plink not having as many features Some users want to generate a large number of SSH keys on Unix and then copy them all into PuTTY and the Unix PuTTYgen should allow them to automate that conversion process There were development advantages as well porting PuTTY to Unix was a valuable path finding effort for other future ports and also allowed us to use th xcellent Linux tool Valgrind to help with debugging which has already improved PuTTY s stability on _all_ platforms However if you re a Unix user and you can see no reason to switch from OpenSSH to PuTTY Plink then you re probably right We don t expect our Unix port to be the right thing for everybody A 3 4 Will there be a port to Windows CE or PocketPC We have done some work on such a port but it only reached an early stage and certainly not a useful one It s no longer being actively worked on However there s a third party port at http www pocketputty net A 3 5 Is there a port to Windows 3 1 PuTTY is a 32 bit application from the ground up so it won t run on Windows 3 1 as a native 16 bit program and it would be _very_ hard to port it to do so because of Windows 3 1 s vile memory allocation mechanisms However it is possible in theory to compile the existing
81. H 1 password camouflage When talking to an SSH 1 server which cannot deal with ignore messages s section 4 24 1 PuTTY will attempt to disguise the length of the user s password by sending additional padding _within_ the password packet This is technically a violation of the SSH 1 specification and so PuTTY will only do it when it cannot use standards compliant ignore messages as camouflage In this sense for a server to refuse to accept a padded password packet is not really a bug but it does make life inconvenient if the server can also not handle ignore messages If this bug is detected PuTTY will assume that neither ignore messages nor padding are acceptable and that it thus has no choice but to send the user s password with no form of camouflage so that an eavesdropping user will be easily able to find out the exact length of the password If this bug is enabled when talking to a correct server the session will succeed but will be more vulnerable to eavesdroppers than it could be http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 58 of 131 This is an SSH 1l specific bug SSH 2 is secure against this type of attack 4 24 3 Chokes on SSH 1 RSA authentication Some SSH 1 servers cannot deal with RSA authentication messages at all If Pageant is running and contains any SSH 1 keys PuTTY will normally automatically try RSA authentication before falling back to pa
82. Jb e5 6f a7 4 9 81 62 5c e3 1f bf 8b 57 6c 5a If you trust this host hit Yes to add the key to PuTTY s cache and carry on connecting If you want to carry on connecting just once without adding the key to the cache hit No If you do not trust this host hit Cancel to abandon the connection This is a feature of the SSH protocol It is designed to protect you against a network attack known as _spoofing_ secretly redirecting your connection to a different computer so that you send your password to the wrong machine Using this technique an attacker would be able to learn the password that guards your login account and could then log in as if they were you and use the account for their own purposes To prevent this attack each server has a unique identifying code called a _host key_ These keys are created in a way that prevents one server from forging another server s key So if you connect to a server and it sends you a different host key from the one you were expecting PuTTY can warn you that the server may have been switched and that a spoofing attack might be in progress PuTTY records the host key for each server you connect to in the Windows Registry Every time you connect to a server it checks that the host key presented by the server is the same host key as it was the last time you connected If it is not you will see a warning and you will have the chance to abandon your connection before
83. NT and even on later versions of Windows 95 but early Win95 installations don t have it In order to use Plink on these systems you will need to download the WinSock 2 upgrade http www microsoft com windows95 downloads contents wuadmintools s_wunetworkingtools w95sockets2 After trying to establish an SSH 2 connection PuTTY says Out of memory and dies If this happens just while the connection is starting up this often indicates that for some reason the client and server have failed to establish a session encryption key Somehow they have performed calculations that should have given each of them the same key but have ended up with different keys so data encrypted by one and decrypted by the other looks like random garbage This causes an out of memory error because the first encrypted data PuTTY expects to see is the length of an SSH message Normally this will be something well under 100 bytes If the decryption has failed PuTTY will see a completely random length in the region of http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 105 of 131 two _gigabytes_ and will try to allocate enough memory to store this non existent message This will immediately lead to it thinking it doesn t have enough memory and panicking If this happens to you it is quite likely to still be a PuTTY bug and you should report it although it might be a bug
84. PuTTY attempts a key re exchange See section 4 19 2 for more about key re exchange It can also occur if you are using keepalives in your connection Other people have reported that keepalives _fix_ this error for them See section 4 13 1 for a discussion of the pros and cons of keepalives We are not aware of any reason why this error might occur that would represent a bug in PuTTY The problem is between you your Windows system your network and the remote system 10 15 Network error Connection reset by peer This error occurs when the machines at each end of a network connection lose track of the state of the connection between them For example you might see it if your SSH server crashes and manages to reboot fully before you next attempt to send data to it However the most common reason to see this message is if you are connecting through a firewall or a NAT router which has timed the connection out See question A 7 10 in the FAQ for more details You may be able to improve the situation by using keepalives s section 4 13 1 for details on this Note that Windows can produce this error in some circumstances without seeing a connection reset from the server for instance if the connection to the network is lost 10 16 Network error Connection refused This error means that the network connection PuTTY tried to make to your server was rejected by the server Usually this happens because
85. PuTTY isa documents PuTTY User Manual PE PuTTY and PuTTYgen _Note to U nix users _ t versions of the PuTTY u MIT licensed his tilities Win32 Tel and its companion utili manual curren Some op that are absent from the Unix version described This manual is copyrigh may distribute this documentation under the MIT licenc her described at all The o exists is the man pages and the nly the licence text in full Chapter 1 Introduction to PuTTY PuTTY is a free SSH systems If you already k What are SSH now what SSH skip on to the next section SSH Multi user opera a command lin or MS DOS Prompt type commands which t Using this type of i at the same machine you are typing commands to and responses computer and give co SSH t T i his Telnet and Telnet and Rlogi On the computer you sit a network connection to the other connection carries your keystro the server hese protocol nteractive session boards access using You might want to use SSH you ting systems nterfac ab i nt n Windows Telnet and Rlogin Telnet and Rlogin are such as Unix and VMS to the user The system prints a prompt he system will obey net and SSH client T ties PSCP PSFTP Pli tly primarily documen Page 1 of 131 his manual nk Pageant ts the Windows tions are there
86. SH Telnet and Rlogin network protocols These protocols are all used to run a remote session on a computer over a network PuTTY implements the client end of that session the end at which the session is displayed rather than the end at which it runs In really simple terms you run PuTTY on a Windows machine and tell it to connect to for example a Unix machine PuTTY opens a window Then anything you type into that window is sent straight to the Unix machine and everything the Unix machine sends back is displayed in the window So you can work on the Unix machine as if you were sitting at its console while actually sitting somewhere else Features supported in PuTTY In general if you want to know if PuTTY supports a particular feature you should look for it on the PuTTY web site In particular try the changes page and see if you can find the feature on there If a feature is listed there it s been implemented If it s listed as a change made _since_ the latest version it should be available in the development snapshots in which case testing will be very welcom try the Wishlist page and see if you can find the feature there If it s on there and not in the Recently fixed section it probably _hasn t_ been implemented A 2 1 Does PuTTY support SSH 2 Yes SSH 2 support has been available in PuTTY since version 0 50 http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 96 of 131
87. The Bugs panel allows you to manually configure the bugs PuTTY expects to see in the server Each bug can be configured in three states Off PuTTY will assume the server does not have the bug On PuTTY will assume the server _does_ have the bug Auto PuTTY will use the server s version number announcement to try to guess whether or not the server has the bug 4 24 1 Chokes on SSH 1 ignore messages An ignore message SSH_MSG_IGNORE is a message in the SSH protocol which can be sent from the client to the server or from the server to the client at any time Either side is required to ignore the message whenever it receives it PuTTY uses ignore messages to hide the password packet in SSH 1 so that a listener cannot tell the length of the user s password it also uses ignore messages for connection keepalives s section 4 13 1 If this bug is detected PuTTY will stop using ignore messages This means that keepalives will stop working and PuTTY will have to fall back to a secondary defence against SSH 1 password length eavesdropping See section 4 24 2 If this bug is enabled when talking to a correct server the session will succeed but keepalives will not work and the session might be more vulnerable to eavesdroppers than it could be This is an SSH 1 specific bug No known SSH 2 server fails to deal with SSH 2 ignore messages 4 24 2 Refuses all SS
88. acters in the list box Then enter a class number in the edit box below and press the Set button This mechanism currently only covers ASCII characters because it isn t feasible to expand the list to cover the whole of Unicode Character class definitions can be modified by control sequences sent by the server This configuration option controls the _default_ state which will be restored when you reset the terminal see section 3 1 3 6 However if you modify this option in mid session using Change Settings it will take effect immediately 4 12 The Colours panel The Colours panel allows you to control PuTTY s use of colour 4 12 1 Allow terminal to specify ANSI colours This option is enabled by default If it is disabled PuTTY will ignore any control sequences sent by the server to request coloured text If you have a particularly garish application you might want to http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 39 of 131 turn this option off and make PuTTY only use the default foreground and background colours 4 12 2 Allow terminal to use xterm 256 colour mode This option is enabled by default If it is disabled PuTTY will ignore any control sequences sent by the server which use the xtended 256 colour mode supported by recent versions of xterm If you have an application which is supposed to use 256 colour mode and it isn t working you may find you need to
89. ailing list if you need to send confidential data as part of a bug report you can trust the people on the list to respect that confidence Also the archives aren t publicly available so you shouldn t be letting yourself in for any spam by sending us mail Please use a meaningful subject line on your message We get a lot of mail and it s hard to find the message we re looking for if they all have subject lines like PuTTY bug B 1 1 Sending large attachments Since the PuTTY contact address is a mailing list e mails larger than 40Kb will be held for inspection by the list administrator and will not be allowed through unless they really appear to be worth their large size If you are considering sending any kind of large data file to the PuTTY team it s almost always a bad idea or at the very least it would be better to ask us first whether we actually need the file Alternatively you could put the file on a web site and just send us the URL that way we don t have to download it unless we decide w actually need it and only one of us needs to download it instead of it being automatically copied to all the developers Some people like to send mail in MS Word format Please _don t_ send us bug reports or any other mail as a Word document Word documents are roughly fifty times larger than writing the same report in plain text In addition most of the PuTTY team read their e
90. am putty 0 60 puttydoc txt 7 11 2008 Page 23 of 131 Most servers send two control characters CR and LF to start a new line of the screen The CR character makes the cursor return to the left hand side of the screen The LF character makes the cursor move one line down and might make the screen scroll Some servers only send LF and expect the terminal to move the cursor over to the left automatically If you come across a server that does this you will s a stepped effect on the screen like this First line of text Second line Third line If this happens to you try enabling the Implicit CR in every LF option and things might go back to normal First line of text Second line Third line 4 3 4 Use background colour to erase screen Not all terminals agree on what colour to turn the screen when th server sends a clear screen sequence Some terminals believe the screen should always be cleared to the _default_ background colour Others believe the screen should be cleared to whatever the server has selected as a background colour There exist applications that expect both kinds of behaviour Therefore PuTTY can be configured to do either With this option disabled screen clearing is always done in the default background colour With this option enabled it is done in the _current_ background colour Background colour erase can be turned on and off by control sequences sent by t
91. an SSH 1 server you can use the unsafe command line option with PSCP pscp unsafe fred example com source c c source This will suppress the warning message and the file transfer will happen However you should be aware that by using this option you are giving the server the ability to write to _any_ file in the target directory so you should only use this option if you trust the server administrator not to be malicious and not to let the server machine be cracked by malicious people Alternatively do any such download in a newly created empty directory Even in unsafe mode PSCP will still protect you against the server trying to get out of that directory using pathnames including 5 22 1l 1 user The login name on the remote server If this is omitted and host is a PuTTY saved session PSCP will use any username specified by that saved session Otherwise PSCP will attempt to use the local Windows username De2ele2 host The name of the remote server or the name of an existing PuTTY saved session In the latter case the session s settings for hostname port number cipher type and username will be used 5 2 1 3 source One or more source files Wildcards are allowed The syntax of wildcards depends on the system to which they apply so if you are copying _from_ a Windows system _to_ a UNIX system you should use Windows wildcard syntax e g but if you are
92. an try entering its name manually CP866 for example in the list box If the underlying version of Windows has the appropriate translation table installed PuTTY will use it Treat CJK ambiguous characters as wide There are some Unicode characters whose width is not well defined In most contexts such characters should be treated as single width for the purposes of wrapping and so on however in some CJK contexts they are better treated as double width for historical reasons and some server side applications may expect them to be displayed as such Setting this option will cause PuTTY to take the double width interpretation If you use legacy CJK applications and you find your lines are wrapping i problems This optio n the wrong places or you are having other display you might want to play with this setting n only has any effect in UTF 8 mode s section 4 10 1 7 11 2008 Page 36 of 131 4 10 3 Caps Lock acts as Cyrillic switch This feature allows you to switch between a US UK keyboard layout and a Cyrillic keyboard layout by using the Caps Lock key if you need to type for example Russian and English side by side in the same document Currently this feature is not expected to work properly if your native keyboard layout is not US or UK 4 10 4 Controlling display of line drawing characters vT100 series terminals allow the server to send control sequences that shi
93. and an easily get into a state where all the text printed becomes nreadable This can happen for example if you accidentally output a binary file to your terminal If this happens selecting Reset Terminal should sort it out cao0oH 3 1 3 7 Full screen mode If you find the title bar on a maximised window to be ugly or distracting you can select Full Screen mode to maximise PuTTY even more When you select this PuTTY will expand to fill the whole screen and its borders title bar and scrollbar will disappear You can configure the scrollbar not to disappear in full screen mode if you want to keep it see section 4 7 3 http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 9 of 131 When you are in full screen mode you can still access the system menu if you click the left mouse button in the _extreme_ top left corner of the screen 3 2 Creating a log file of your session For some purposes you may find you want to log everything that appears on your screen You can do this using the Logging panel in the configuration box To begin a session log select Change Settings from the system menu and go to the Logging panel Enter a log file name and select a logging mode You can log all session output including the terminal control sequences or you can just log the printable text It depends what you want the log for Click Apply and your log will be started Later
94. aphic characters if your keyboard http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 has any However Ctr he setting of ct AltGr acts as Compose key Page 28 of 131 Alt will never act as a Compose key regardless of described in section 4 4 7 4 5 The Bell panel he Bell panel controls the terminal bell feature the server s ability to cause PuTTY to beep at you In the default configuration when the server sends the character with ASCII code 7 Control G PuTTY will play the Windows Default Beep sound This is not always what you want the terminal bell feature to do the Bell panel allows you to configure alternative actions 4 5 1 Set the style of bell This control allows you to select various different actions to occur on a terminal bell Selecting None disables the bell completely In this mode the server can send as many Control G characters as it likes and nothing at all will happen Make default system alert sound is the default setting It causes the Windows Default Beep sound to be played To change what this sound is or to test it if nothing seems to be happening use the Sound configurer Panel in the Windows Control Visual bell is a silent alternative to a beeping computer In this mode when the server sends a Control G the whole PuTTY window will flash white for a fracti
95. appear in the window to indicate this 8 2 5 The Key fingerprint box The Key fingerprint box shows you a fingerprint value for the generated key This is derived cryptographically from the _public_ key value so it doesn t need to be kept secret The fingerprint value is intended to be cryptographically secure in the sense that it is computationally infeasible for someone to invent a second key with the same fingerprint or to find a key with a particular fingerprint So some utilities such as the Pageant key list box see section 9 2 1 and the Unix ssh add utility will list key fingerprints rather than the whole public key 8 2 6 Setting a comment for your key If you have more than one key and use them for different purposes you don t need to memorise the key fingerprints in order to tell them apart PuTTYgen allows you to enter a _comment_ for your key which will be displayed whenever PuTTY or Pageant asks you for the passphrase The default comment format if you don t specify one contains the key type and the date of generation such as rsa key 20011212 Another commonly used approach is to use your name and the name of the computer the key will be used on such as simon simons pc To alter the key comment just type your comment text into the Key comment box before saving the private key If you want to change the comment later you can load the private key back into PuTTYgen
96. associated with SSH 2 servers is specified in a more platform independent way and leaves issues such as wildcard syntax up to the client PuTTY s SFTP wildcard syntax is described in section 6 2 2 This makes it more consistent across platforms more suitable for scripting and automation and avoids security issues with wildcard matching Normally PSCP will attempt to use the SFTP protocol and only fall back to the SCP protocol if SFTP is not available on the server The scp option forces PSCP to use the SCP protocol or quit The sftp option forces PSCP to use the SFTP protocol or quit When this option is specified PSCP looks harder for an SFTP server which may allow use of SFTP with SSH 1 depending on server setup 5 2 3 Return value PSCP returns an ERRORLEVEL of zero success only if the files were correctly transferred You can test for this in a batch file using code such as this pscp file user hostname if errorlevel 1 echo There was an error 5 2 4 Using public key authentication with PSCP Like PuTTY PSCP can authenticate using a public key instead of a password There are thr ways you can do this Firstly PSCP can use PuTTY saved sessions in place of hostnames see section 5 2 1 2 So you would do this Run PuTTY and create a PuTTY saved session see section 4 1 2 which specifies your private key file s section 4 20 7 You will probably also want to specify
97. at you ve tried to load a key of an inappropriate type into PuTTY Plink PSCP PSFTP or Pageant You may have specified a key that s inappropriate for the connection you re making The SSH 1 and SSH 2 protocols require different private key formats and a SSH 1 key can t be used for a SSH 2 connection or vice versa Alternatively you may have tried to load an SSH 2 key ina foreign format OpenSSH or ssh com directly into one of the PuTTY tools in which case you need to import it into PuTTY s native format PPK using PuTTYgen see section 8 2 12 10 9 Server refused our public key or Key refused Various forms of this error are printed in the PuTTY window or written to the PuTTY Event Log see section 3 1 3 1 when trying public key authentication If you see one of these messages it means that PuTTY has sent a public key to the server and offered to authenticate with it and the server has refused to accept authentication This usually means that the server is not configured to accept this key to authenticate this user This is almost certainly not a problem with PuTTY If you see this type of message the first thing you should do is check your _server_ configuration carefully Common errors include having the wrong permissions or ownership set on the public key or the user s home directory on the server Also read the PuTTY Event Log the server may have sent diagnostic messages explaining exact
98. can do this in two ways Set up a PuTTY saved session that describes the server you are connecting to and that also specifies a private key file see section 4 20 7 For this to work without prompting your private key will need to have no passphrase Store the private key in Pageant See chapter 9 for further information http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 78 of 131 Once you have done all this you should be able to run a remote command on the SSH server machine and have it execute automatically with no prompting Z sysosd gt plink login example com 1 fred echo hello world hello world Z sysosd gt Or if you have set up a saved session with all the connection details Z sysosd gt plink mysession echo hello world hello world Z sysosd gt Then you can set up other programs to run this Plink command and talk to it as if it were a process on the server machine 7 2 3 Plink command line options Plink accepts all the general command line options supported by the PuTTY tools See section 3 8 3 for a description of these options Plink also supports some of its own options The following sections describe Plink s specific command line options 7 2 3 1 batch disable all interactive prompts If you use the batch option Plink will never give an interactive prompt while establishing the connection If the server s host key is invalid for exampl s sec
99. changes to these settings take effect immediately My PuTTY sessions unexpectedly close after they are idle fora while Some types of firewall and almost any router doing Network Address Translation NAT also known as IP masquerading will forget about a connection through them if the connection does nothing for too long This will cause the connection to be rudely cut off when contact is resumed You can try to combat this by telling PuTTY to send _keepalives_ packets of data which have no effect on the actual session but which reassure the router or firewall that the network connection is still active and worth remembering about Keepalives don t solve everything unfortunately although they cause greater robustness against this sort of router they can also cause a _loss_ of robustness against network dropouts See section 4 13 1 in the documentation for more discussion of this PuTTY s network connections time out too quickly when network connectivity is temporarily lost This is a Windows problem not a PuTTY problem The timeout value can t be set on per application or per session basis To increase the TCP timeout globally you need to tinker with the Registry On Windows 95 98 or ME the registry key you need to create or change is HKEY_LOCAL_MACHINE System CurrentControlSet Services VxD STCP MaxDataRetries Ea it must be of type DWORD in Win95 or String in Win98 M Knowledge Base arti
100. changing PuTTY has the ability to change the window title in respons to commands from the server If you find PuTTY is doing this unexpectedly or inconveniently you can tell PuTTY not to respond to those server commands 4 6 6 Response to remote window title querying PuTTY can optionally provide the xterm service of allowing server applications to find out the local window title This feature is disabled by default but you can turn it on if you really want it NOTE that this feature is a _potential security hazard_ If a malicious application can write data to your terminal for example if you merely cat a file owned by someone else on the server machine it can change your window title unless you have disabled this as mentioned in section 4 6 5 and then use this service to have the new window title sent back to the server as if typed at the keyboard This allows an attacker to fake keypresses and potentially cause your server side applications to do things you didn t want Therefore this feature is disabled by default and we recommend you do not set it to Window title unless you _really_ know what you are doing There are thr settings for this option None PuTTY makes no response whatsoever to the relevant escap sequence This may upset server side software that is expecting some sort of response Empty string PuTTY makes a well formed response but leaves it bla
101. chieve this A 9 2 Would you like free web hosting for the PuTTY web site We already have some thanks A 9 3 Would you link to my web site from the PuTTY web site Only if the content of your web page is of definite direct interest to PuTTY users If your content is unrelated or only tangentially related to PuTTY then the link would simply be advertising for you One very nice effect of the Google ranking mechanism is that by and large the most popular web sites get the highest rankings This means that when an ordinary person does a search the top item in the search is very likely to be a high quality site or the site they actually wanted rather than the site which paid the most money for its ranking he PuTTY web site is held in high esteem by Google for precisely this reason lots of people have linked to it simply because they like PuTTY without us ever having to ask anyone to link to us We feel that it would be an abuse of this esteem to use it to boost the ranking of random advertisers web sites If you want your web site to have a high Google ranking we d prefer that you achieve this the way we did by being good enough at what you do that people will link to you simply because they like you http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 112 of 131 In particular we aren t interested in trading links for money see above and we _certainly_ aren t in
102. cle 158474 for more information See MS On Windows NT 2000 or XP the registry key to create or change is HKEY_LOCAL_MACHINE SYSTEM CurrentControlSet Services Tcpip Parameters TcpMaxDataRetransmissions and it must be of type DWORD See MS Knowledge Base articles 120642 and 314053 for more information Set the key s value to something like 10 This will cause Windows to try harder to keep connections alive instead of abandoning them When I cat a binary file I get PuTTYPuTTYPuTTY on my command line Don t do that then This is designed behaviour when PuTTY receives the character Control E from the remote server it interprets it as a request to identify itself and so it sends back the string PuTTY as if that string had been entered at the keyboard Control E should only be sent by programs that are prepared to deal with the response Writing a binary file to your terminal is likely to output many Control E characters and cause this behaviour Don t do it It s a bad plan http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 A 7 13 A 7 14 As Teta Page 107 of 131 To mitigate the effects you could configure the answerback string to be empty see section 4 3 6 but writing binary files to your terminal is likely to cause various other unpleasant behaviour so this is only a small remedy When I cat a binary file my window title
103. configuration box This allows you to adjust most properties of your current session You can change the terminal size the font the actions of various keypresses the colours and so on Some of the options that are available in the main configuration box are not shown in the cut down Change Settings box These are usually options which don t make sense to change in the middle of a session for example you can t switch from SSH to Telnet in mid session You can save the current settings to a saved session for future use from this dialog box See section 4 1 2 for more on saved sessions 3 1 3 5 Copy All to Clipboard This system menu option provides a convenient way to copy the whole contents of the terminal screen up to the last nonempty line and scrollback to the clipboard in one go 3 1 3 6 Clearing and resetting the terminal The Clear Scrollback option on the system menu tells PuTTY to discard all the lines of text that have been kept after they scrolled off the top of the screen This might be useful for example if you displayed sensitive information and wanted to make sure nobody could look over your shoulder and see it Note that this only prevents a casual user from using the scrollbar to view the information the text is not guaranteed not to still be in PuTTY s memory he Reset Terminal option causes a full reset of the terminal mulation A VTI series terminal is a complex piece of software
104. cting select the first key type or your Th key typ two types he PuTTY developers _strongly_ recommend you use RSA DSA has an intrinsic weakness which makes it very easy to create a signature which contains enough information to give away the This would allow an attacker to pretend to be you for any number PuTTY s implementation has taken very careful but we cannot be 100 and if you have the choice we strongly recommend _private_ key certain we If you really need to connect to an SSH server which only supports DSA DSA more than one server Selecting the size The Number of bits strength then you probably have no choice but to use DSA we recommend you do not us th sam of the key the key PuTTYgen will generate If you do use key to authenticate with input box allows you to choose the strength of Currently 1024 bits should be sufficient for most purposes Note that an RSA key is generated by finding two primes of half the length requested and then multiplying them together if you ask PuTTYgen for a 1024 bit RSA key http the earth li sgtatham putty 0 60 puttydoc txt For example it will create two 512 7 11 2008 Page 82 of 131 bit primes and multiply them The result of this multiplication might be 1024 bits long or it might be only 1023 so you may not get the exact length of key you asked for This is perfectly normal and you do not need to worry
105. d by the SSH server and can run X applications which are forwarded over the SSH connection However the second user root does not automatically have the authentication data passed on to it http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 94 of 131 so attempting to run an X application as that user often fails with this error If this happens _it is not a problem with PuTTY_ You need to arrange for your X authentication data to be passed from the user you logged in as to the user you used su to become How you do this depends on your particular system in fact many modern versions of su do it automatically 10 14 Network error Software caused connection abort This is a generic error produced by the Windows network code when it kills an established connection for some reason For example it might happen if you pull the network cable out of the back of an Ethernet connected computer or if Windows has any other similar reason to believe th ntire network has become unreachable Windows also generates this error if it has given up on the machine at the other end of the connection ever responding to it If the network between your client and server goes down and your client then tries to send some data Windows will make several attempts to send the data and will then give up and kill the connection In particular this can occur even if you didn t type anything if you are using SSH 2 and
106. d do the code which fixes eport However a pa eport if your patch won t be able to fi g uk sgtatham bugs welcome to try to fix the a bug is an tch is never a is wrong or t supplied us with full information nda better html is an article on how to report bugs effectively in general If your unclear we may ask you to go away bug report is _particularly_ read this article and then r eport the bug again It is reasonable to report bugs in PuTTY s documentation if you r or unhelpful But we do need to be given exact details of _what_ you think the documentation you think it could be made clearer If your problem is simply that you don t _understand_ the think the documentation is unclea has failed to tell you or _how_ documentation we suggest posting to a newsgroup see section B 1 2 and seeing if someone will explain what you need to know _Then_ if you think the documentation could usefully have told you that send us a bug report and explain how you think we should change it B 3 Requesting extra features If you want to request a new feat you should do are Check the Wishlist page on th feature is already on the lis achieve very much to repeat t ure in PuTTY the very first things e PuTTY website and see if your t If it is it probably won t he request But see section B 4 if you want to persuade us to give your particular feature higher pri
107. d password D listen IP listen port Dynamic SOCKS based port forwarding L listen IP listen port host port Forward local port to remote address R listen IP listen port host port Forward remote port to local address X xX enable disable X11 forwarding A a enable disable agent forwarding t I enable disable pty allocation mal 2 force use of particular protocol version 4 6 force use of IPv4 or IPv6 C enable compression i key private key file for authentication noagent disable use of Pageant agent enable use of Pageant m fil read remote command s from file s remote command is an SSH subsystem SSH 2 only N don t start a shell command SSH 2 only ne host port open tunnel in place of session SSH 2 only Once this works you are ready to use Plink 7 2 1 Using Plink for interactive logins To make a simple interactive connection to a remote server just type plink and then the host name Z sysosd gt plink login example com Debian GNU Linux 2 2 flunky example com flunky login You should then be able to log in as normal and run a session The output sent by the server will be written straight to your command prompt window which will most likely not interpret terminal control codes in the way the server expects it to So if you run any full screen applications for example you can expect to see strange characters appearing in your window Interactive connections like this are no
108. delete a forwarding any existing connections established using that forwarding remain open Similarly changes to global settings such as Local ports accept connections from other hosts only take effect on new forwardings 4 23 1 Controlling the visibility of forwarded ports The source port for a forwarded connection usually does not accept connections from any machine except the SSH client or server machine itself for local and remote forwardings respectively There are controls in the Tunnels panel to change this The Local ports accept connections from other hosts option allows you to set up local to remote port forwardings in such a way that machines other than your client PC can connect to the forwarded port This also applies to dynamic SOCKS forwarding The Remote ports do the same option does the same thing for remote to local port forwardings so that machines other than the SSH server machine can connect to the forwarded port Note that this feature is only available in the SSH 2 protocol and not all SSH 2 servers support it OpenSSH 3 0 does not for example 4 23 2 Selecting Internet protocol version for forwarded ports This switch allows you to select a specific Internet protocol IPv4 or IPv6 for the local end of a forwarded port By default it is set on Auto which means that for a local to remote port forwarding PuTTY will listen for incoming connections in both IPv4 and i
109. directories browse around the file system issue multiple get and put commands and eventually log out By contrast PSCP is designed to do a single file transfer operation and immediately terminate 6 1 Starting PSFTP The usual way to start PSFTP is from a command prompt much like PSCP To do this it will need either to be on your PATH or in your current directory To add the directory containing PSFTIP to your PATH environment variable type into the console window set PATH C path to putty directory sPATHS Unlike PSCP however PSFTP has no complex command line syntax you just specify a host name and perhaps a user name psftp server example com or perhaps psftp fred server example com Alternatively if you just type psftp on its own or double click the PSFTP icon in the Windows GUI you will see the PSFTP prompt and a message telling you PSFTP has not connected to any server C gt psftp http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 67 of 131 psftp no hostname specified use open host name to connect psftp gt At this point you can type open server example com or open fred server example com to start a session PSFTP accepts all the general command line options supported by the PuTTY tools xcept the ones which make no sense in a file transfer utility See section 3 8 3 for a description of these options The ones not supported by PSFTP are
110. disable it using the Disable xterm style mouse reporting control With this box ticked the mouse will _always_ do copy and paste in the normal way http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 30 of 131 Note that even if the application takes over the mouse you can still manage PuTTY s copy and paste by holding down the Shift key while you select and paste unless you have deliberately turned this feature off see section 4 11 3 4 6 3 Disabling remote terminal resizing PuTTY has the ability to change the terminal s size and position in response to commands from the server If you find PuTTY is doing this unexpectedly or inconveniently you can tell PuTTY not to respond to those server commands 4 6 4 Disabling switching to the alternate screen Many terminals including PuTTY support an alternate screen This is the same size as the ordinary terminal screen but separate Typically a screen based program such as a text editor might switch the terminal to the alternate screen before starting up Then at the end of the run it switches back to the primary screen and you see the screen contents just as they were before starting the editor Some people prefer this not to happen If you want your editor to run in the same screen as the rest of your terminal activity you can disable the alternate screen feature completely 4 6 5 Disabling remote window title
111. dom numbers at all For this reason we now believe PuTTY s DSA implementation is probably OK However if you have the choice we still recommend you use RSA instead A 8 4 Couldn t Pageant use VirtualLock to stop private keys being written to disk Unfortunately not The VirtualLock function in the Windows API doesn t do a proper job it may prevent small pieces of a process s memory from being paged to disk while the process is running but it doesn t stop the process s memory as a whole from being swapped completely out to disk when the process is long term inactive And Pageant spends most of its time inactive A 9 Administrative questions A 9 1 Would you like me to register you a nicer domain name No thank you Even if you can find one most of them seem to have been registered already by people who didn t ask whether we actually wanted it before they applied we re happy with the PuTTY web site being exactly where it is It s not hard to find just type putty into google com and we re the first link returned and we don t believe the administrative hassle of moving the site would be worth the benefit In addition if we _did_ want a custom domain name we would want to run it ourselves so we knew for certain that it would continue to point where we wanted it and wouldn t suddenly change or do strange things Having it registered for us by a third party who we don t even know is not the best way to a
112. don t trust the network then the PuTTY download might be tampered with so it would be better to carry PuTTY with you ona floppy A 8 2 What does PuTTY leave on a system How can I clean up after it PuTTY will leave some Registry entries and a random seed file on the PC see question A 5 2 If you are using PuTTY on a public PC or somebody else s PC you might want to clean these up when you leave You can do that automatically by running the command putty cleanup Note that this only removes settings for the currently logged in user on multi user systems If PuTTY was installed from the installer package it will also appear in Add Remove Programs Older versions of the uninstaller do not remove the above mentioned registry entries and file A 8 3 How come PuTTY now supports DSA when the website used to say how insecure it was DSA has a major weakness _if badly implemented_ it relies ona random number generator to far too great an extent If the random number generator produces a number an attacker can predict the DSA private key is exposed meaning that the attacker can log in as you http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 111 of 131 on all systems that accept that key The PuTTY policy changed because the developers were informed of ways to implement DSA which do not suffer nearly as badly from this weakness and indeed which don t need to rely on ran
113. dows user name or in case you didn t bother to set up a Windows user name 4 18 The SSH panel The SSH panel allows you to configure options that only apply to SSH sessions 4 18 1 Executing a specific command on the server In SSH you don t have to run a general shell session on the server Instead you can choose to run a single specific command such as a mail user agent for example If you want to do this enter the command in the Remote command box Note that most servers will close the session after executing the command 4 18 2 Don t start a shell or command at all If you tick this box PuTTY will not attempt to run a shell or command after connecting to the remote server You might want to use this option if you are only using the SSH connection for port forwarding and your user account on the server does not have the http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 A823 4 18 4 As B25 Page 48 of 131 ability to run a shell This feature is only available in SSH protocol version 2 since the version 1 protocol assumes you will always want to run a shell This feature can also be enabled using the N command line option see section 3 8 3 13 If you use this feature in Plink you will not be able to terminate the Plink process by any graceful means the only way to kill it will be by pressing Control C or sending a kill signal from another program
114. e Therefore embedding Windows specific code in core modules such as ssh c is not acceptable We went to great lengths to _remove_ all the Windows specific stuff from our core modules and to shift it out into Windows specific modules Adding large amounts of Windows specific stuff in parts of the code that should be portable is almost guaranteed to make us reject a contribution The PuTTY source base is divided into platform specific modules and platform generic modules The Unix specific modules are all in the unix subdirectory the Mac specific modules are in the mac subdirectory the Windows specific modules are in the windows subdirectory All the modules in the main source directory notably _all_ of the code for the various back ends are platform generic We want to keep them that way This also means you should stick to what you are guaranteed by ANSI ISO C that is the original C89 C90 standard not C99 Try not to make assumptions about the precise size of basic types such as int and long int don t use pointer casts to do endianness dependent operations and so on http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 124 of 131 There are one or two aspects of ANSI C portability which we _don t_ care about In particular we expect PuTTY to be compiled on 32 bit architectures _or bigger_ so it s safe to assume that int is at least 32 bits wide not just t
115. e http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 75 of 131 command line with the i option See section 3 8 3 18 for more information Thirdly PSFTP will attempt to authenticate using Pageant if Pageant is running see chapter 9 So you would do this Ensure Pageant is running and has your private key stored in it Specify a user and host name to PSFTP as normal PSFTP will automatically detect Pageant and try to use the keys within it For more general information on public key authentication see chapter 8 Chapter 7 Using the command line connection tool Plink Plink PuTTY Link is a command line connection tool similar to UNIX ssh It is mostly used for automated operations such as making CVS access a repository on a remote server Plink is probably not what you want if you want to run an interactive session in a console window 7 1 Starting Plink Plink is a command line application This means that you cannot just double click on its icon to run it and instead you have to bring up a console window In Windows 95 98 and ME this is called an MS DOS Prompt and in Windows NT 2000 and XP it is called a Command Prompt It should be available from the Programs section of your Start Menu In order to use Plink the file plink exe will need either to be on your PATH or in your current directory To add the directory containing Plink to your PATH
116. e couldn t possibly comment on such allegations How do I pronounce PuTTY Exactly like the English word putty which we pronounce pVti Appendix B Feedback and bug reporting This is a guide to providing feedback to the PuTTY development team It is provided as both a web page on the PuTTY site and an appendix in the PuTTY manual Section B 1 gives some general guidelines for sending any kind of e mail to the development team Following sections give more specific guidelines for particular types of e mail such as bug reports and feature requests General guidelines The PuTTY development team gets a _lot_ of mail If you can possibly solve your own problem by reading the manual reading the FAQ reading the web site asking a fellow user perhaps posting to a newsgroup see section B 1 2 or some other means then it would make our lives much easier We get so much e mail that we literally do not have time to answer it all We regret this but there s nothing we can do about it So if you can _possibly_ avoid sending mail to the PuTTY team we http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 117 of 131 recommend you do so In particular support requests section B 5 are probably better sent to newsgroups or passed to a local expert if possible The PuTTY contact email address is a private mailing list containing four or five core developers Don t be put off by it being a m
117. e 19 of 131 rate from the Default Settings To save a session first go through the rest of the configuration box setting up all the options you want Then come back to the Session panel Enter a name for the saved session in the Saved Sessions input box The server name is often a good choice for a saved session name Then press the Save button Your saved session name should now appear in the list box You can also save settings in mid session from the Change Settings dialog Settings changed since the start of the session will be saved with their current values as well as settings changed through the dialog this includes changes in window size window title changes sent by the server and so on To reload a saved session single click to select the session name in the list box and then press the Load button Your saved settings should all appear in the configuration panel To modify a saved session first load it as described above Then make the changes you want Come back to the Session panel and press the Save button The new settings will be saved over the top of the old ones To save the new settings under a different name you can enter the new name in the Saved Sessions box or single click to select a session name in the list box to overwrite that session To save Default Settings you must single click the name before saving To start a saved session immediately double click o
118. e between security and convenience See chapter 9 for further details There is more than one public key algorithm available The most common is RSA but others exist notably DSA otherwise known as DSS the USA s federal Digital Signature Standard The key types supported by PuTTY are described in section 8 2 2 8 2 Using PuTTYgen the PuTTY key generator PuTTYgen is a key generator It generates pairs of public and private keys to be used with PuTTY PSCP and Plink as well as the PuTTY authentication agent Pageant see chapter 9 PuTTYgen generates RSA and DSA keys When you run PuTTYgen you will see a window where you have two choices Generate to generate a new public private key pair or Load to load in an existing private key 8 2 1 Generating a new key This is a general outline of the procedure for generating a new key pair The following sections describe the process in more detail First you need to select which type of key you want to generate and also select the strength of the key This is described in more detail in section 8 2 2 and section 8 2 3 http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 22 adie 2 Then press the Generat button Section 8 2 4 describes this step Once you hav 8 2 6 and a passphrase Now you re ready to save the private key to disk Save private key button Your key pair is now ready for use
119. e deliberately kept just small enough to fit comfortably on a 640x480 display If you re adding controls to either of these boxes and you find yourself wanting to increase the size of the whole box _don t_ Split it into more panels instead D 11 Automatically generated Makefiles PuTTY is intended to compile on multiple platforms and with multiple compilers It would be horrifying to try to maintain a single Makefile which handled all possible situations and just as painful to try to directly maintain a set of matching Makefiles for each different compilation environment Therefore we have moved the problem up by one level In the PuTTY source archive is a fil called Recipe which lists which source files combine to produce which binaries and there is also a script called mkfiles pl which reads Recipe and writes out the real Makefiles The script also reads all the source files and analyses their dependencies on header files so we get an extra benefit from doing it this way which is that we can supply correct dependency information even in environments where it s difficult to set up an automated make depend phase You should _never_ edit any of the PuTTY Makefiles directly They are not stored in our source repository at all They are automatically generated by mkfiles pl from the file Recipe If you need to add a new object file to a particular binary the right thi
120. e file transfer using the reget and reput commands These work exactly like the get and put commands but they check for the presence of the half written destination file and start transferring from where the last attempt left off http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 6 2 13 6 2 14 http the earth li sgtatham putty 0 60 puttydoc txt The syntax of of get and Page 72 of 131 reget and reput is exactly the same as the syntax puts reget myfile dat reget myfile dat newname dat reget i These comma transfers has not cha pick up cha The dir nds are intended They assume that nged in any way up with corrupted files nges to files or command To list the files in your remote working directory mydir mainly for resuming interrupted the remote file or directory structure if there have been changes you may end particular the r option will not directories already transferred in full In list remote files just type dir You can also list the contents of a different directory by typing Gir dir home dir sources And you can followed by the directory name fred list a subset of the contents of a directory by providing a wildcard dir home Fred txt dir sources c The ls command works exactly the same way as dir The chmod command change permissions on remote fi
121. e flexible and mor secure S for a full discussion of public key A 2 9 Is there an option to turn off the annoying host key prompts No there isn t And there won and send us the patch we won t Those annoying host key prompts Without them all the cryptogra a packet sniffer the attacker must actuall start modifying the packets goi that much harder than just snif it will go completely undetected by client or server Host key checking is your guara on your data at the client end the data at the server end it been removed and replaced somew t be Even if you wr accept it ite it yourself are the _whole point_ of SSH phic technology SSH uses to secure your session is doing nothing more than making an attacker s job slightly harder instead of sitting between you and the server with ly subvert a router and ng back and forth But that s not all fing and without ho ntee that the encryp is the _same_ encryp s your guarantee tha makes the attacker s job _astro sniffing and even compared to applying a little intelligenc attacker must now perform a bru here on the way Hos subverting a router and keeping an eye o te force attack agai st key checking tion you put tion taken off t it hasn t t key checking nomically_ hard compared to packet Instead of n Bugtraq the nst at least one military strength cipher That insignificant host key prompt rea
122. e proxy without trying to look them up first If you set this option to Auto the default PuTTY will do something it considers appropriate for each type of proxy Telnet HTTP and SOCKS5 proxies will have host names passed straight to them SOCKS4 proxies will not Note that if you are doing DNS at the proxy you should make sure that your proxy exclusion settings see section 4 15 2 do not depend on knowing the IP address of a host If the name is passed on to the proxy without PuTTY looking it up it will never know the IP address and cannot check it against your list The original SOCKS 4 protocol does not support proxy side DNS There is a protocol extension SOCKS 4A which does support it but not all SOCKS 4 servers provide this extension If you enable proxy DNS and your SOCKS 4 server cannot deal with it this might be why 4 15 4 Username and password If your proxy requires authentication you can enter a username and a password in the Username and Password boxes Note that if you save your session the proxy password will be saved http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 45 of 131 in plain text so anyone who can access your PuTTY configuration data will be able to discover it Authentication is not fully supported for all forms of proxy Username and password authentication is supported for HTTP proxies and SOCKS 5 proxies With SOCKS 5 authentication is via CHAP
123. e quotes For example this command psftp gt ren this a file with quotes in it will take a file whose current name is this with a double quote character at the beginning and the end and rename it to a file whose name is a file with quotes in it http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 69 of 131 The one exception to the PSFTP quoting rules is the command which passes its command line straight to Windows without splitting it up into words at all See section 6 2 19 6 2 2 Wildcards in PSFTP Several commands in PSFTP support wildcards to select multiple files For _local_ file specifications such as the first argument to put wildcard rules for the local operating system are used For instance PSFTP running on Windows might require the use of where PSFTP on Unix would need For _remote_ file specifications such as the first argument to get PSFTP uses a standard wildcard syntax similar to POSIX wildcards matches any sequence of characters including a zero length sequence matches exactly one character abc matches exactly one character which can be a b or c a z matches any character in the range a to z abc matches a single character that is _not_ a b orc Special cases a matches a literal hyphen or a a matches all other characters a matches a literal caret o
124. e who happen to do some stuff in our spare time Therefore to ask us to assume financial liability is to ask us to assume a risk of having to pay it out of our own _personal_ pockets out of the same budget from which we buy food and clothes and pay our rent That s more than we re willing to give We re already giving a lot of our spare _time_ to developing software for free if we had to pay our own _money_ to do it as well we d start to wonder why we were bothering http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 A 9 10 A 9 11 A 9 12 Page 114 of 131 Free software fundamentally does not work on the basis of financial guarantees Your guarantee of the software functioning correctly is simply that you have the source code and can check it before you use it If you want to be sure there aren t any security holes do a security audit of the PuTTY code or hire a security engineer if you don t have the necessary skills yourself instead of trying to ensure you can get compensation in the event of a disaster try to ensure there isn t a disaster in the first place If you _really_ want financial security see if you can finda security engineer who will take financial responsibility for the correctness of their review This might be less likely to suffer from the everything failing at once problem mentioned above because such an engineer would probably be reviewing a lot of _different_ products
125. ection 4 1 1 if the connection type is set to Serial 4 25 2 Selecting the speed of your serial line The Speed box allows you to choose the speed or baud rate at which to talk to the serial line Typical values might be 9600 19200 38400 or 57600 Which one you need will depend on the device at the other end of the serial cable consult the manual for that device if you are in doubt This configuration setting is also visible on the Session panel where it replaces the Port box see section 4 1 1 if the connection type is set to Serial http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 60 of 131 4 25 3 Selecting the number of data bits The Data bits box allows you to choose how many data bits are transmitted in each byte sent or received through the serial line Typical values are 7 or 8 4 25 4 Selecting the number of stop bits The Stop bits box allows you to choose how many stop bits are used in the serial line protocol Typical values are 1 1 5 or 2 4 25 5 Selecting the serial parity checking scheme The Parity box allows you to choose what type of parity checking is used on the serial line The settings are None no parity bit is sent at all Odd an extra parity bit is sent alongside each byte and arranged so that the total number of 1 bits is odd Even an extra parity bit is sent alongside each byte and arranged so that the
126. ed this to debug a network level problem or more likely to send to the PuTTY authors as part of a bug report _BE WARNED_ that if you log in using a password the password can appear in the log file see section 4 2 4 for options that may help to remove sensitive material from the log file before you send it to anyone else SSH packets and raw data In this mode as well as the decrypted packets as in the previous mode the _raw_ encrypted compressed etc packets are _also_ logged This could be useful to diagnose corruption in transit The same caveats as the previous mode apply of course ote that the non SSH logging options Printable output and All ession output only work with PuTTY proper in programs without erminal emulation such as Plink they will have no effect even f enabled via saved settings og file name n this edit box you enter the name of the file you want to log the ession to The Browse button will let you look around your file ystem to find the right place to put the file or if you already now exactly where you want it to go you can just type a pathname nto the edit box here are a few special features in this box If you use the amp haracter in the file name box PuTTY will insert details of the urrent session in the name of the file it actually opens The recise replacements it will do are amp Y will be replaced by the curr
127. ee section 3 1 3 2 Max minutes before rekey specifies the amount of time that is allowed to elapse before a rekey is initiated If this is set to zero PuTTY will not rekey due to elapsed time The SSH 2 protocol specification recommends a timeout of at most 60 minutes You might have a need to disable time based rekeys completely for the same reasons that keepalives aren t always helpful If you anticipate suffering a network dropout of several hours in the middle of an SSH connection but were not actually planning to send _data_ down that connection during those hours then an attempted rekey in the middle of the dropout will probably cause the connection to be abandoned whereas if rekeys are disabled then the connection should in principle survive in the absence of interfering firewalls See section 4 13 1 for more discussion of these issues for these purposes rekeys have much the same properties as keepalives Except that rekeys have cryptographic value in themselves so you should bear that in mind when deciding whether to turn them off Note however the the SSH _server_ can still initiate rekeys Max data before rekey specifies the amount of data in bytes that is permitted to flow in either direction before a rekey is initiated If this is set to zero PuTTY will not rekey due to transferred data The SSH 2 protocol specification recommends a limit of at most 1 gigabyte
128. elected Bolded text is a different colour and can also be used if the server asks specifically to use them Note that Default Bold Background is _not_ the background colour used for bold text it is only used if the server specifically asks for a bold background 4 13 The Connection panel The Connection panel allows you to configure options that apply to more than one type of connection 4 13 1 Using keepalives to prevent disconnection If you find your sessions are closing unexpectedly most often with Connection reset by peer after they have been idle for a while you might want to try using this option Some network routers and firewalls need to keep track of all connections through them Usually these firewalls will assume a connection is dead if no data is transferred in either direction after a certain time interval This can cause PuTTY sessions to be unexpectedly closed by the firewall if no traffic is seen in the session for some time The keepalive option Seconds between keepalives allows you to configure PuTTY to send data through the session at regular intervals in a way that does not disrupt the actual terminal session If you find your firewall is cutting idle connections off you can try entering a non zero value in this field The value is measured in seconds so for example if your firewall cuts connections off after ten minutes then you might want to enter 30
129. ell 4 12 5 Use system colours Enabling this option will cause PuTTY to ignore the configured colours for Default Background Foreground and Cursor Colour Text see section 4 12 6 instead going with the system wide defaults Note that non bold and bold text will be the same colour if this option is enabled You might want to change to indicating bold text by font changes see section 4 12 3 4 12 6 Adjusting the colours in the terminal window The main colour control allows you to specify exactly what colours things should be displayed in To modify one of the PuTTY colours use the list box to select which colour you want to modify The RGB values for that colour will appear on the right hand side of the list box Now if you press the Modify button you will be presented with a colour selector in which you can choose a new colour to go in place of the old one You may also edit the RGB http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 40 of 131 values directly in the edit boxes if you wish each value is an integer from 0 to 255 PuTTY allows you to set the cursor colour the default foreground and background and the precise shades of all the ANSI configurable colours black red green yellow blue magenta cyan and white You can also modify the precise shades used for the bold versions of these colours these are used to display bold text if you have s
130. emote machine s finger port then you should be able to run commands such as finger fred 127 0 0 5 This can be useful if the program connecting to the forwarded port doesn t allow you to change the port number it uses This feature is available for local to remote forwarded ports SSH 1 is unable to support it for remote to local ports while SSH 2 can support it in theory but servers will not necessarily cooperate Note that if you re using Windows XP Service Pack 2 you may need to obtain a fix from Microsoft in order to use addresses lik 127 0 0 5 see question A 7 20 3 6 Making raw TCP connections A lot of Internet protocols are composed of commands and responses in plain text For example SMTP the protocol used to transfer e mail NNTP the protocol used to transfer Usenet news and HTTP the protocol used to serve Web pages all consist of commands in readable plain text Sometimes it can be useful to connect directly to one of these services and speak the protocol by hand by typing protocol commands and watching the responses On Unix machines you can do this using the system s telnet command to connect to the right port number For example telnet mailserver example com 25 might enable you to talk directly to the SMTP service running on a mail server http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 12 of 131 Although the Unix telnet program provides t
131. ent year as four digits amp M will be replaced by the current month as two digits http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 21 of 131 amp D will be replaced by the current day of the month as two digits amp T will be replaced by the current time as six digits HHMMSS with no punctuation amp H will be replaced by the host name you are connecting to For example if you enter the host name c puttylogs log amp h amp y m amp d amp t dat you will end up with files looking like log serverl example com 20010528 110859 dat log unixbox somewhere org 20010611 221001 dat 4 2 2 What to do if the log file already exists This control allows you to specify what PuTTY should do if it tries to start writing to a log file and it finds the file already exists You might want to automatically destroy the existing log file and start a new one with the same name Alternatively you might want to open the existing log file and add data to the _end_ of it Finally the default option you might not want to have any automatic behaviour but to ask the user every time the problem comes up 4 2 3 Flush log file frequently This option allows you to control how frequently logged data is flushed to disc By default PuTTY will flush data as soon as it is displayed so that if you view the log file while a ses
132. eone can solve your problem Or try doing the same thing with a different SSH client and see if it works with that Please do not report it as a PuTTY bug unless you are really sure it _is_ a bug in PuTTY If someone else installed PuTTY for you or you re using PuTTY on someone else s computer try asking them for help first They re more likely to understand how they installed it and what they expected you to use it for than we are If you have successfully made a connection to your server and now need to know what to type at the server s command prompt or other details of how to use the server end software talk to your server s system administrator This is not the PuTTY team s problem PuTTY is only a communications tool like a telephone if you can t speak the same language as the person at the other end of the phone it isn t the telephone company s job to teach it to you If you absolutely cannot get a support question answered any other way you can try mailing it to us but we can t guarantee to have time to answer it B 6 Web server administration If the PuTTY web site is down Connection Timed Out please don t bother mailing us to tell us about it Most of us read our e mail on the same machines that host the web site so if those machines are down then we will notice _before_ we read our e mail So there s no point telling us our servers are down Of course if the web site has some other
133. er from the ground up We don t tivation The code is available if have time and we don t have mo anyone else wants to try it A 2 11 Can PSCP or PSFTP transfer file Unfortunately not s in ASCII mode http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 33 3a 3 s Page 98 of 131 Until recently this was a limitation of the file transfer protocols the SCP and SFTP protocols had no notion of transferring a file in anything other than binary mode This is still true of SCP The current draft protocol spec of SFTP proposes a means of implementing ASCII transfer At some point PSCP PSFTP may implement this proposal Ports to other operating systems The eventual goal is for PuTTY to be a multi platform program able to run on at least Windows Mac OS and Unix Porting will becom asier once PuTTY has a generalised porting layer drawing a clear line between platform dependent and platform independent code The general intention was for this porting layer to evolve naturally as part of the process of doing the first port a Unix port has now been released and the plan seems to be working so far What ports of PuTTY exist Currently release versions of PuTTY tools only run on full Win32 systems and Unix Win32 includes Windows 95 98 and ME and it includes Windows NT Windows 2000 and Windows XP In the development code a partial port to the Mac OS see question A 3 6
134. error Connection Refused 404 Not Found 403 Forbidden or something else then we might _not_ have noticed and it might still be worth telling us about it If you want to report a problem with our web site check that you re looking at our _real_ web site and not a mirror The real web sit is at http www chiark greenend org uk sgtatham putty if that s not where you re reading this then don t report the problem to us until you ve checked that it s really a problem with the main site If it s only a problem with the mirror you should try to contact the administrator of that mirror site first and only contact us if that doesn t solve the problem in case we need to remove the mirror from our list B 7 Asking permission for things PuTTY is distributed under the MIT Licence s appendix C for http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 122 of 131 details This means you can do almost _anything_ you like with our software our source code and our documentation The only things you aren t allowed to do are to remove our copyright notices or the licence text itself or to hold us legally responsible if something goes wrong So if you want permission to include PuTTY on a magazine cover disk or as part of a collection of useful software on a CD or a web site then _permission is already granted_ You don t have to mail us and ask Just go ahead and do it We don t mind
135. f available IPv6 for a remote to local port forwarding PuTTY will choose a sensible protocol for the outgoing connection Note that some operating systems may listen for incoming connections in IPv4 even if you specifically asked for IPv6 because their IPv4 and IPv6 protocol stacks are linked together Apparently Linux does this and Windows does not So if you re running PuTTY on Windows and you tick IPv6 for a local or dynamic port forwarding it will _only_ be usable by connecting to it using IPv6 whereas if you do the same on Linux you can also use it with IPv4 However ticking Auto should always give you a port which you can connect to using either protocol 4 24 The Bugs panel http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 57 of 131 Not all SSH servers work properly Various existing servers have bugs in them which can make it impossible for a client to talk to them unless it knows about the bug and works around it Since most servers announce their software version number at the beginning of the SSH connection PuTTY will attempt to detect which bugs it can expect to see in the server and automatically enable workarounds However sometimes it will make mistakes if the server has been deliberately configured to conceal its version number or if the server is a version which PuTTY s bug database does not know about then PuTTY will not know what bugs to expect
136. f necessary introduce a second new source file defining the same set of functions but defining them as stubs which don t provide the feature Then th module whose behaviour needs to vary proxy c in this example can call the functions defined in these two modules and it will either 7 11 2008 14 Page 129 of 131 provide the new feature or not provide it according to which of your new modules it is linked with Of course object files are never shared _between_ platforms so it is allowable to use ifdef to select between platforms This happens in puttyps h choosing which of the platform specific include files to use and also in misc c the Windows specific Minefield memory diagnostic system It should be used sparingly though if at all Do as we say not as we do The current PuTTY code probably does not conform strictly to _all_ of the principles listed above There may be the occasional SSH specific piece of code in what should be a backend independent module or the occasional dependence on a non standard X library function under Unix This should not be taken as a licence to go ahead and violate the rules Where we violate them ourselves we re not happy about it and we would welcome patches that fix any existing problems Please try to help us make our code better not worse Appendix E PuTTY download keys and signatures ti We create PGP signatures for all the P
137. f the same setup We have not yet got round to this at the time of writing We have collected a few third party signatures on the Master Keys in order to increase the chances that you can find a suitable trust path to them We intend to collect more Note that the keys on the keyservers appear to have also collected some signatures from people who haven t performed any verification of the Master Keys We have uploaded our various keys to public keyservers so that even if you don t know any of the people who have signed our keys you can still be reasonably confident that an attacker would find it hard to substitute fake keys on all the public keyservers at once PuTTY release 0 60 http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008
138. f your server sends text written in the basic Unicode Arabic alphabet then it will convert it to the correct display forms before printing it on the screen If you are using full screen software which was not expecting this to happen especially if you are not an Arabic speaker and you unexpectedly find yourself dealing with Arabic text files in applications which are not Arabic aware you might find that the display becomes corrupted By ticking this box you can disable Arabic text shaping so that PuTTY displays precisely the characters it is told to display You may also find you need to disable bidirectional text display see section 4 6 10 4 6 10 Disabling bidirectional text display PuTTY supports bidirectional text display which means that if your server sends text written in a language which is usually displayed from right to left such as Arabic or Hebrew then PuTTY will automatically flip it round so that it is displayed in the right direction on the screen If you are using full screen software which was not expecting this to happen especially if you are not an Arabic speaker and you unexpectedly find yourself dealing with Arabic text files in applications which are not Arabic aware you might find that the display becomes corrupted By ticking this box you can disable bidirectional text display so that PuTTY displays text from left to right in all situations You may als
139. for the Unix version has f pterm and command line puttygen utili Unix specific documentation that currently m ntioned eatures not ties are not t 2001 2007 Simon Tatham All rights reserved You S Y us much like the C can b rface there is no need for you The co sent over a network so you can mmands to N are and carries th a _network protocols_ tha nother one wee or even to t al you run a _client_ computer the _server_ k to talker systems and MUDs lnet Ther there are a lot of Multi User Dungeons ar have a Telnet or Rlogin if able to access from somewhere else you on A you r Internet Servic a web server r commands for you http the earth li sgtatham putty 0 60 puttydoc txt appendix C for Telnet and Rlogin client for 32 bit Windows ou can safely Rlogin are three ways of doing the same thing logging in to a multi user computer from another computer network overa ually present ommand Prompt and you to be sitting mmands sit at one more than one low you to do which makes a The network kes and commands from the client to server s responses bac you ls can also be used for other types of keyboard based In particular bulletin which support ven a few that support SSH n account on a Unix or VMS system which you want to be Provider provides you with a l
140. free time we may sometimes be willing to give up some more of our free time in exchange for some money but if you try to bribe us fora _big_ feature it s entirely possible that we simply won t have the time to spare whether you pay us or not Also we don t accept bribes to add _bad_ features to the Wishlist because our desire to provide high quality software to the users comes first Offer to help us write the code This is probably the _only_ way to get a feature implemented quickly if it s a big one that we don t have time to do ourselves B 5 Support requests http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 121 of 131 If you re trying to make PuTTY do something for you and it isn t working but you re not sure whether it s a bug or not then _please_ consider looking for help somewhere else This is one of the most common types of mail the PuTTY team receives and we simply don t have time to answer all the questions Questions of this type include If you want to do something with PuTTY but have no idea where to start and reading the manual hasn t helped try posting to a newsgroup see section B 1 2 and see if someone can explain it to you If you have tried to do something with PuTTY but it hasn t worked and you aren t sure whether it s a bug in PuTTY or a bug in your SSH server or simply that you re not doing it right then try posting to a newsgroup see section B 1 2 and see if som
141. ft temporarily into a separate character set for drawing simple lines and boxes However there are a variety of ways in which PuTTY can attempt to find appropriate characters and the right one to use depends on the locally configured font In general you should probably try lots of options until you find one that your particular font supports Use Unicode line drawing code points tries to use the box characters that are present in Unicode For good Unicode supporting fonts this is probably the most reliable and functional option Poor man s line drawing assumes that the font _cannot_ generate the line and box characters at all so it will use the and characters to draw approximations to boxes You should use this option if none of the other options works Font has XWindows encoding is for use with fonts that have a special encoding where the lowest 32 character positions below the ASCII printable range contain the line drawing characters This is unlikely to be the case with any standard Windows font it will probably only apply to custom built fonts or fonts that have been automatically converted from the X Window System Use font in both ANSI and OEM modes tries to use the same font in two different character sets to obtain a wider range of characters This doesn t always work some fonts claim to be a different size depending on which character set you try to use
142. ge the default settings that are used for new sessions See section 4 1 2 in the documentation for how to do this A 2 6 Does PuTTY support storing its settings in a disk file Not at present although section 4 26 in the documentation gives a method of achieving the same effect A 2 7 Does PuTTY support full screen mode like a DOS box Yes this is a new feature in version 0 52 A 2 8 Does PuTTY have the ability to remember my password so I don t have to type it every time No it doesn t Remembering your password is a bad plan for obvious security reasons anyone who gains access to your machine while you re away from your desk can find out the remembered password and use it abuse it or change it In addition it s not even _possible_ for PuTTY to automatically send your password in a Telnet session because Telnet doesn t give the client software any indication of which part of the login process is the password prompt PuTTY would have to guess by looking for words like password in the session data and if your login program is written in something other than English this won t work http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 97 of 131 In SSH remembering your password would be possible in theory but there doesn t seem to be much point since SSH supports public key authentication which is mo chapter 8 in the documentation authentication r
143. gs if supplied Also you can specify a protocol which will override the default protocol see section 3 8 3 2 http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 13 of 131 For telnet sessions the following alternative syntax is supported this makes PuTTY suitable for use as a URL handler for telnet URLs in web browsers putty exe telnet host port In order to start an existing saved session called sessionname use the load option described in section 3 8 3 1 putty exe load session name 3 8 2 cleanup If invoked with the cleanup option rather than running as normal PuTTY will remove its registry entries and random seed file from the local machine after confirming with the user Note that on multi user systems cleanup only removes registry entries and files associated with the currently logged in user 3 8 3 Standard command line options PuTTY and its associated tools support a range of command line options most of which are consistent across all the tools This section lists the available options in all tools Options which are specific to a particular tool are covered in the chapter about that tool 3 8 3 1 load load a saved session The load option causes PuTTY to load configuration details out of a saved session If these details include a host name then this option is all you need to make PuTTY start a session You need double quotes
144. h li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 130 of 131 DSA Master Key Release key Snapshot key Master Key 1024 bit fingerprint 313C 3E76 4B74 C2C5 F2AE 83A8 4F5E 6DF5 6A93 B341 T Gl E 2 Security details The various keys have various different security levels This section explains what those security levels are and how far you can expect to trust each key N he Development Snapshots keys hese keys are stored _without passphrases_ This is necessary because the snapshots are generated every night without human intervention so nobody would be able to type a passphrase he actual snapshots are built on a team member s home Windows box he keys themselves are stored on an independently run Unix box the same one that hosts our Subversion repository After being built the binaries are uploaded to this Unix box and then signed automatically Therefore a signature from one of the Development Snapshots keys _DOES_ protect you against People tampering with the PuTTY binaries between the PuTTY web site and you But it _DOES NOT_ protect you against People tampering with the binaries before they are uploaded to the independent Unix box The sysadmin of the independent Unix box using his root privilege to steal the private keys and abuse them or tampering with the binaries before they are signed Somebody getting
145. he 16 you are guaranteed by ANSI C Similarly we assume that the execution character encoding is a superset of the printable characters of ASCII though we don t assume the numeric values of control characters particularly n and r D 2 Multiple backends treated equally PuTTY is not an SSH client with some other stuff tacked on the side PuTTY is a generic multiple backend remote VT terminal client which happens to support one backend which is larger more popular and more useful than the rest Any extra feature which can possibly be general across all backends should be so localising features unnecessarily into the SSH back end is a design error For example we had several code submissions for proxy support which worked by hacking ssh c Clearly this is completely wrong the network h abstraction is the place to put it so that it will apply to all back ends equally and indeed we eventually put it there after another contributor sent a better patch The rest of PuTTY should try to avoid knowing anything about specific back ends if at all possible To support a feature which is only available in one network protocol for example the back end interface should be extended in a general manner such that _any_ back end which is able to provide that feature can do so If it so happens that only one back end actually does that s just the way it is but it shouldn t be relied upon by any code
146. he Kex panel he Kex panel short for key exchange allows you to configure options related to SSH 2 key exchange Key exchange occurs at the start of an SSH connection and occasionally thereafter it establishes a shared secret that is used as the basis for all of SSH s security features It is therefore very important for the security of the connection that the key exchange is secure Key exchange is a cryptographically intensive process if either the client or the server is a relatively slow machine the slower methods may take several tens of seconds to complete If connection startup is too slow or the connection hangs periodically you may want to try changing these settings If you don t understand what any of this means it s safe to leave these settings alone This entire panel is only relevant to SSH protocol version 2 none of these settings affect SSH 1 at all 4 19 1 Key exchange algorithm selection PuTTY supports a variety of SSH 2 key exchange methods and allows you to choose which one you prefer to use configuration is similar to cipher selection see section 4 18 5 PuTTY currently supports the following varieties of Diffie Hellman key exchange Group 14 a well known 2048 bit group Group 1 a well known 1024 bit group This is less secure than group 14 but may be faster with slow client or server machines and may be the only method supported by older server
147. he local one put myfile dat newname dat This will send the local file called myfile dat but will store it on the server under the name newname dat To send an entire directory recursively you can use the r option put r mydir put r mydir newname If you want to send a file whose name starts with a hyphen you may have to use the special argument which stops put from interpreting anything as a switch after it For example put silly name 6 2 11 The mget and mput commands fetch or send multiple files mget works almost exactly like get except that it allows you to specify more than one file to fetch at once You can do this in two ways by giving two or more explicit file names mget filel txt file2 txt by using a wildcard mget txt Every argument to mget is treated as the name of a file to fetch unlike get which will interpret at most one argument like that and a second argument will be treated as an alternative name under which to store the retrieved file or a wildcard expression matching more than one file The r and options from get are also available with mget mput is similar to put with the same differences 6 2 12 The reget and reput commands resuming file transfers If a file transfer fails half way through and you end up with half the file stored on your disk you can resume th
148. he server This configuration option controls the _default_ state which will be restored when you reset the terminal see section 3 1 3 6 However if you modify this option in mid session using Change Settings it will take effect immediately 4 3 5 Enable blinking text The server can ask PuTTY to display text that blinks on and off This is very distracting so PuTTY allows you to turn blinking text off completely When blinking text is disabled and the server attempts to make some text blink PuTTY will instead display the text with a bolded background colour Blinking text can be turned on and off by control sequences sent by the server This configuration option controls the _default_ state which will be restored when you reset the terminal see section 3 1 3 6 However if you modify this option in mid session using Change Settings it will take effect immediately 4 3 6 Answerback to E This option controls what PuTTY will send back to the server if the server sends it the E enquiry character Normally it just sends the string PuTTY http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 24 of 131 If you accidentally write the contents of a binary file to your terminal you will probably find that it contains more than one character and as a result your next command line will probably read PuTTYPuTTYPuTlTY as if you had typed the answerback st
149. his functionality the protocol being used is not really Telnet Really there is no actual protocol at all the bytes sent down the connection are exactly the ones you type and the bytes shown on the screen ar xactly the ones sent by the server Unix telnet will attempt to detect or guess whether the service it is talking to is a real Telnet servic or not PuTTY prefers to be told for certain In order to make a debugging connection to a service of this type you simply select the fourth protocol name Raw from the Protocol buttons in the Session configuration panel See section 4 1 1 You can then enter a host name and a port number and make the connection 3 7 Connecting to a local serial line PuTTY can connect directly to a local serial line as an alternative to making a network connection In this mode text typed into the PuTTY window will be sent straight out of your computer s serial port and data received through that port will be displayed in the PuTTY window You might use this mode for example if your serial port is connected to another computer which has a serial connection To make a connection of this type simply select Serial from the Connection type radio buttons on the Session configuration panel see section 4 1 1 The Host Name and Port boxes will transform into Serial line and Speed allowing you to specify which serial
150. hostile environment and security is everybody s responsibility If you are connecting across the open Internet then we recommend you use SSH If the server you want to connect to doesn t support SSH it might be worth trying to persuade the administrator to install it If your client and server are both behind the same good firewall it is more likely to be safe to use Telnet or Rlogin but we still recommend you use SSH Chapter 2 Getting started with PuTTY This chapter gives a quick guide to the simplest types of interactive login session using PuTTY 2 1 Starting a session When you start PuTTY you will see a dialog box This dialog box allows you to control everything PuTTY can do See chapter 4 for details of all the things you can control You don t usually need to change most of the configuration options To start the simplest kind of session all you need to do is to enter a few basic parameters In the Host Name box enter the Internet host name of the server you want to connect to You should have been told this by the provider of your login account Now select a login protocol to use from the Connection type buttons For a login session you should select Telnet Rlogin or http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 3 of 131 SSH See section 1 2 for a description of the differences between the three protocols and advice on which one to use The f
151. if the proxy supports it this is not supported in PuTTYtel otherwise the password is sent to the proxy in plain text With HTTP proxying the only currently supported authentication method is basic where the password is sent to the proxy in plain text SOCKS 4 can use the Username field but does not support passwords You can specify a way to include a username and password in the Telnet Local proxy command see section 4 15 5 4 15 5 Specifying the Telnet or Local proxy command If you are using the Telnet proxy type the usual command required by the firewall s Telnet server is connect followed by a host name and a port number If your proxy needs a different command you can enter an alternative here If you are using the Local proxy type the local command to run is specified here In this string you can use n to represent a new line r to represent a carriage return t to represent a tab character and x followed by two hex digits to represent any other character Y Al is used to encode the character itself so the special strings host and port will be replaced by the host name and port number you want to connect to The strings Suser and pass will be replaced by the proxy username and pa be ssword you specify The strings proxyhost and proxyport will replaced by the host details specified on the _Proxy_ panel if any this
152. ifferent formats and PuTTY s is different again So a key generated with one client cannot immediately be used with another Using the Import command from the Conversions menu PuTTYgen can load SSH 2 private keys in OpenSSH s format and ssh com s format Once you have loaded one of these key types you can then save it back out as a PuTTY format key PPK so that you can use it with http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 85 of 131 the PuTTY suite The passphrase will be unchanged by this process unless you deliberately change it You may want to change the key comment before you save the key since OpenSSH s SSH 2 key format contains no space for a comment and ssh com s default comment format is long and verbose PuTTYgen can also export private keys in OpenSSH format and in ssh com format To do so select one of the Export options from the Conversions menu Exporting a key works exactly like saving it see section 8 2 8 you need to have typed your passphrase in beforehand and you will be warned if you are about to save a key without a passphrase Note that since only SSH 2 keys come in different formats the export options are not available if you have generated an SSH 1 key 8 3 Getting ready for public key authentication Connect to your SSH server using PuTTY with the SSH protocol When the connection succeeds you will be prompted for your user name and password to
153. ifies a standard format for storing SSH 2 public keys on disk Some SSH servers such as ssh com s require a public key in this format in order to accept authentication with the corresponding private key Others such as OpenSSH use a different format see section 8 2 10 http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 84 of 131 To save your public key in the SSH 2 standard format press the Save public key button in PuTTYgen PuTTYgen will put up a dialog box asking you where to save the file Select a directory type ina file name and press Save You will then probably want to copy the public key file to your SSH server machine See section 8 3 for general instructions on configuring public key authentication once you have generated a key If you use this option with an SSH 1 key the file PuTTYgen saves will contain exactly the same text that appears in the Public key for pasting box This is the only existing standard for SSH 1 public keys 8 2 10 Public key for pasting into authorized_keys file All SSH 1 servers require your public key to be given to it ina one line format before it will accept authentication with your private key The OpenSSH server also requires this for SSH 2 The Public key for pasting into authorized_keys file gives the public key data in the correct one line format Typically you will want to select th ntire contents of the box using the mo
154. ill all circumstances The precis depends on the mode all of the available modes ar ffec ost ame nce m S O Some your heir names come ht to fro valu hese settings will have any effect if Ly or and hitting can be removed from the list by selecti ffect of the mode list is as follows m the drop down Add A mode you If you don t understand any no pseudo terminal to a specific value or ng them and hitting not be specified to the be sent to th syntax of the value box listed as option is selected the PuTTY tools will decide whether to specify that mode to the server will send a sensibl nd modes that it has an opinion on currently only the code for the Backspace key ERASE the and if server under f each setting m POSIX and other Unix systems if any is up to the server and they are Auto thing in most circumstances which likely to have a useful effect on such systems These are the settings that can usually be changed using the stty command logged in to such servers notable modes are described below for fuller explanations see server documentation ERASE is the character that when typed by the user will delete one space to the left When set to Auto the default setting this follows the setting of the local Backspace key in PuTTY see section 4 4 1
155. ils see appendix B For more options relating to X11 forwarding see section 4 22 3 5 Using port forwarding in SSH The SSH protocol has the ability to forward arbitrary network connections over your encrypted SSH connection to avoid the network traffic being sent in clear For example you could use this to connect from your home computer to a POP 3 server ona remote machine without your POP 3 password being visible to network sniffers In order to use port forwarding to connect from your local machine to a port on a remote server you need to Choose a port number on your local machine where PuTTY should listen for incoming connections There are likely to be plenty of unused port numbers above 3000 You can also use a local loopback address here s below for more details Now before you start your SSH connection go to the Tunnels panel see section 4 23 Make sure the Local radio button is set Enter the local port number into the Source port box Enter the destination host name and port number into the Destination box separated by a colon for example popserver example com 110 to connect to a POP 3 server Now click the Add button The details of your port forwarding should appear in the list box Now start your session and log in Port forwarding will not be enabled until after you have logged in otherwise it would be easy to perform completely anonymous network attacks and ga
156. in access to anyone s virtual private network To check that PuTTY has set up the port forwarding correctly you can look at the PuTTY Event Log see section 3 1 3 1 It should say something like this 2001 12 05 17 22 10 Local port 3110 forwarding to popserver example com 110 Now if you connect to the source port number on your local PC you should find that it answers you exactly as if it were the servic running on the destination machine So in this example you could then configure an e mail client to use localhost 3110 as a POP 3 server instead of popserver example com 110 Of course the forwarding will stop happening when your PuTTY session closes down You can also forward ports in the other direction arrange for a particular port number on the _server_ machine to be forwarded back to your PC as a connection to a service on your PC or near it To do http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 11 of 131 this just select the Remote radio button instead of the Local one The Source port box will now specify a port number on the _server_ note that most servers will not allow you to use port numbers under 1024 for this purpose An alternative way to forward local connections to remote hosts is to use dynamic SOCKS proxying For this you will need to select the Dynamic radio button instead of Local and then you should not enter anything into the Destinatio
157. in your SSH server instead but it doesn t necessarily mean you ve actually run out of memory A 7 6 When attempting a file transfer either PSCP or PSFTP says Out of memory and dies This is almost always caused by your login scripts on the server generating output PSCP or PSFTP will receive that output when they were expecting to see the start of a file transfer protocol and they will attempt to interpret the output as file transfer protocol This will usually lead to an out of memory error for much the same reasons as given in question A 7 5 3 his is a setup problem in your account on your server _not_ a PSCP PSFTP bug Your login scripts should _never_ generate output during non interactive sessions secure file transfer is not the only form of remote access that will break if they do On Unix a simple fix is to ensure that all the parts of your login script that might generate output are in profile if you use a Bourne shell derivative or login if you use a C shell Putting t t hem in more general files such as bashrc or cshrc is liable o lead to problems A 7 7 PSFTP transfers files much slower than PSCP The throughput of PSFTP 0 54 should be much better than 0 53b and prior we ve added code to the SFTP backend to queue several blocks of data rather than waiting for an acknowledgement for each The SCP backend did not suffer from this performance issue because SCP
158. ing invoking it again with the options http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 88 of 131 below causes actions to be performed with the existing instance not a new one 9 3 1 Making Pageant automatically load keys on startup Pageant can automatically load one or more private keys when it starts up if you provide them on the Pageant command line Your command line might then look like C PuTTY pageant exe d main ppk d secondary ppk If the keys are stored encrypted Pageant will request the passphrases on startup If Pageant is already running this syntax loads keys into the existing Pageant 9 3 2 Making Pageant run another program You can arrange for Pageant to start another program once it has initialised itself and loaded any keys specified on its command line This program perhaps a PuTTY or a WinCVS making use of Plink or whatever will then be able to use the keys Pageant has loaded You do this by specifying the c option followed by the command like this C PuTTY pageant exe d main ppk c C PuTTY putty exe 9 4 Using agent forwarding Agent forwarding is a mechanism that allows applications on your SSH server machine to talk to the agent on your client machine Note that at present agent forwarding in SSH 2 is only available when your SSH server is OpenSSH The ssh com server uses a different agent protocol which PuTTY does not yet support
159. ing Ctrl PgUp and Ctrl PgDn These are still available if you configure the scrollbar to be invisible By default the last 200 lines scrolled off the top are preserved for you to look at You can increase or decrease this value using the configuration box see section 4 7 3 3 1 3 The System menu If you click the left mouse button on the icon in the top left corner of PuTTY s terminal window or click the right mouse button on the title bar you will see the standard Windows system menu containing items like Minimise Move Size and Close PuTTY s system menu contains extra program features in addition to the Windows standard options These extra menu commands are described below These options are also available in a context menu brought up by holding Ctrl and clicking with the right mouse button anywhere in the PuTTY window 3 1 3 1 The PuTTY Event Log If you choose Event Log from the system menu a small window will pop up in which PuTTY logs significant events during the connection Most of the events in the log will probably take place during session startup but a few can occur at any point in the session and one or two occur right at the end You can use the mouse to select one or more lines of the Event Log and hit the Copy button to copy them to the clipboard If you are reporting a bug it s often useful to paste the contents of the Event Log into your bug report 3 1 3 2
160. ing code you should be aware that you might be re entered if a network event comes in and is passed on to our window procedure by loop Also the front ends threads if they lik However control of its auxiliary threads exclusively as a form of select windows winplink c is _only_ ever thread se in particular Windows Windows Plink the others just loop round blocking on file the MessageBox message Plink can use multiple keeps _very_ tight and uses them pretty much Pretty much all the code outside called from the one primary handles and real wor wi case One important consequence of this which to do everything That more than one login session channels within an SSH session http the earth li sgtatham putty 0 60 puttydoc txt nd messages to the main thread when som This is not considered a portability hazard because ndows winplink c will need rewriting on other pla everything section D 3 responding to GUI k needs doing that bit of tforms in any ne thread in may include managing managing multiple data vents even when PuTTY has only o 7 11 2008 Page 127 of 131 nothing is happening on the network and responding to network requests from the server such as repeat key exchange even when th program is dealing with complex user interaction such as the re configuration dialog box This means that _almost none_ of the PuTTY code can safely block
161. ing without limitation the rights to use copy modify merge publish distribute sublicense and or sell copies of the Software a Ss nd to permit persons to whom the Software is furnished to do so ubject to the following conditions he above copyright notice and this permission notice shall be ncluded in all copies or substantial portions of the Software H HE SOFTWARE IS PROVIDED AS IS WITHOUT WARRANTY OF ANY KIND EXPRESS OR IMPLIED INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM DAMAGES OR OTHER LIABILITY WHETHER IN AN ACTION OF CONTRACT ORT OR OTHERWISE ARISING FROM OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE H W lt E T Appendix D PuTTY hacking guide This appendix lists a selection of the design principles applying to the PuTTY source code If you are planning to send code contributions you should read this first D 1 Cross OS portability Despite Windows being its main area of fame PuTTY is no longer a Windows only application suite It has a working Unix port a Mac port is in progress more ports may or may not happen at a later dat
162. ion 4 20 5 These options are not available in the file transfer tools PSCP and PSFTP http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 16 of 131 3 8 3 11 X and x control X11 forwarding The X option turns on X11 forwarding in SSH and x turns it off These options are only meaningful if you are using SSH For information on X11 forwarding see section 3 4 These options are equivalent to the X11 forwarding checkbox in the Tunnels panel of the PuTTY configuration box see section 4 22 These options are not available in the file transfer tools PSCP and PSFTP 3 8 3 12 t and T control pseudo terminal allocation The t option ensures PuTTY attempts to allocate a pseudo terminal at the server and T stops it from allocating one These options are only meaningful if you are using SSH These options are equivalent to the Don t allocate a pseudo terminal checkbox in the SSH panel of the PuTTY configuration box see section 4 21 1 These options are not available in the file transfer tools PSCP and PSFTP 3 8 3 13 N suppress starting a shell or command The N option prevents PuTTY from attempting to start a shell or command on the remote server You might want to use this option if you are only using the SSH connection for port forwarding and your user account on the server does not have the ability to run a shell This feature is only availab
163. ions are equivalent to selecting your preferred SSH protocol version as 1 only or 2 only in the SSH panel of the PuTTY configuration box see section 4 18 4 3 8 3 17 4 and 6 specify an Internet protocol version The 4 and 6 options force PuTTY to use the older Internet protocol IPv4 or the newer IPv6 These options are equivalent to selecting your preferred Internet protocol version as IPv4 or IPv6 in the Connection panel of the PuTTY configuration box see section 4 13 4 3 8 3 18 i specify an SSH private key The i option allows you to specify the name of a private key file in PPK format which PuTTY will use to authenticate with the server This option is only meaningful if you are using SSH For general information on public key authentication see chapter 8 This option is equivalent to the Private key file for authentication box in the Auth panel of the PuTTY configuration box see section 4 20 7 3 8 3 19 pgpfp display PGP key fingerprints This option causes the PuTTY tools not to run as normal but instead to display the fingerprints of the PuTTY PGP Master Keys in order to aid with verifying new versions See appendix E for more information http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 18 of 131 Chapter 4 Configuring PuTTY This chapter describes all the configuration options in PuTTY PuTTY is configured using the contr
164. is most likely to be useful for the Local proxy type To oo get a literal sign enter If a Telnet proxy server prompts for a username and password before commands can be sent you can use a command such as Th to Suser n pass nconnect Shost port n is will send your username and password as the first two lines the proxy followed by a command to connect to the desired host and port Note that if you do not include the user or pass tokens in the Telnet command then the Username and Password configuration fields will be ignored lnet panel N e lnet panel allows you to configure options that only apply to lnet sessions 4 16 1 Handling of OLD_ENVIRON ambiguity The original Telnet mechanism for passing environment variables was http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 ly specifie telnet imp intention lementation Page 46 of 131 d At the time the standard RFC 1408 was written lementations were already supporting the feature and of the standard was to describe the behaviour the BSD s were already using Sadl impl here was a vital func ntations di yt two eme typing error in the standard when it was issued tion codes were specified the wrong way round BSD d not change and the standard was not corrected ssible you might find either BSD or RFC compliant 4 16 2 4 16
165. it from the menu Closing the Pageant main window does _not_ shut down Pageant The Pageant main window The Pageant main window appears when you left click on the Pageant system tray icon or alternatively right click and select View Keys from the menu You can use it to keep track of what keys are currently loaded into Pageant and to add new ones or remove the existing keys http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 87 of 131 9 2 1 The key list box The large list box in the Pageant main window lists the private keys that are currently loaded into Pageant The list might look something like this sshl 1024 22 c3 68 3b 09 41 36 C3 39 83 9l ae 71 b2 0f 04 kl ssh rsa 1023 74 63 08 82 95 75 e1 7 33 31 bb cb 00 c0 89 8b k2 For each key the list box will tell you The type of the key Currently this can be sshl an RSA key for use with the SSH 1 protocol ssh rsa an RSA key for use WwW t ith the SSH 2 protocol or ssh dss a DSA key for use with he SSH 2 protocol he size in bits of the key The fingerprint for the public key This should be the same fingerprint given by PuTTYgen and hopefully also the same fingerprint shown by remote utilities such as ssh keygen when applied to your authorized_keys file The comment attached to the key 9 2 2 The Add Key button To add a key to Pageant by reading it out of a local disk file
166. l deactivate itself Bell overload mode is always deactivated by any keypress in the terminal This means it can respond to large unexpected streams of data but does not interfere with ordinary command line activities that generate beeps such as filename completion 4 6 The Features panel PuTTY s terminal emulation is very highly featured and can do a lot of things under remote server control Some of these features can cause problems due to buggy or strangely configured server applications The Features configuration panel allows you to disable some of PuTTY s more advanced terminal features in case they cause trouble 4 6 1 Disabling application keypad and cursor keys Application keypad mode see section 4 4 5 and application cursor keys mode see section 4 4 4 alter the behaviour of the keypad and cursor keys Some applications enable these modes but then do not deal correctly with the modified keys You can force these modes to be permanently disabled no matter what the server tries to do 4 6 2 Disabling xterm style mouse reporting PuTTY allows the server to send control codes that let it take over the mouse and use it for purposes other than copy and paste Applications which use this feature include the text mode web browser links the Usenet newsreader trn version 4 and the file manager mc Midnight Commander If you find this feature inconvenient you can
167. l top row of the numeric keypad generates ESC OP through to ESC OS In VT100 mode the function keys generate ESC OP through to ESC O In SCO mode the function keys Fl to F12 generate ESC M through to ESC X Together with shift they generate ESC Y through to ESC j With control they generate ESC k through to ESC v and with shift and control together they generat ESC w through to ESC If you don t know what any of this means you probably don t need to fiddle with it 4 4 4 Controlling Application Cursor Keys mode Application Cursor Keys mode is a way for the server to change the control sequences sent by the arrow keys In normal mode the arrow keys send ESC A through to ESC D In application mode they send ESC OA through to ESC OD Application Cursor Keys mode can be turned on and off by the server depending on the application PuTTY allows you to configure the initial state You can also disable application cursor keys mode completely using the Features configuration panel see section 4 6 1 4 4 5 Controlling Application Keypad mode Application Keypad mode is a way for the server to change the behaviour of the numeric keypad In normal mode the keypad behaves like a normal Windows keypad with NumLock on the number keys generate numbers and with NumLock off they act like the arrow
168. le in SSH protocol version 2 since the version 1 protocol assumes you will always want to run a shell This option is equivalent to the Don t start a shell or command at all checkbox in the SSH panel of the PuTTY configuration box see section 4 18 2 This option is not available in the file transfer tools PSCP and PSFTP 3 8 3 14 nc make a remote network connection in place of a remote shell or command The nc option prevents Plink or PuTTY from attempting to start a shell or command on the remote server Instead it will instruct the remote server to open a network connection to a host name and port number specified by you and treat that network connection as if it were the main session You specify a host and port as an argument to the nc option with a colon separating the host name from the port number like this plink hostl example com nc host2 example com 1234 You might want to use this feature if you needed to make an SSH connection to a target host which you can only reach by going through a proxy host and rather than using port forwarding you prefer to use the local proxy feature s section 4 15 1 for more about local proxies In this situation you might select Local proxy type set your local proxy command to be plink proxyhost http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 17 of 131 nc sShost port enter the target host name on the Session
169. lecting Telnet allows you to tell PuTTY to use this type of proxy Selecting Local allows you to specify an arbitrary command on the local machine to act as a proxy When the session is started instead of creating a TCP connection PuTTY runs the command specified in section 4 15 5 and uses its standard input and output streams This could be used for instance to talk to some kind of network proxy that PuTTY does not natively support or you could tunnel a connection over something other than TCP IP entirely If you want your local proxy command to make a secondary SSH connection to a proxy host and then tunnel the primary connection over that you might well want the nc command line option in Plink See section 3 8 3 14 for more information 4 15 2 Excluding parts of the network from proxying Typically you will only need to use a proxy to connect to non local parts of your network for example your proxy might be required for connections outside your company s internal network In the Exclude Hosts IPs box you can enter ranges of IP addresses or ranges of DNS names for which PuTTY will avoid using the proxy and make a direct connection instead http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 44 of 131 The Exclude Hosts IPs box may contain more than one exclusion range separated by commas Each range can be an IP address or a DNS name with a character
170. led by the Terminal type string setting in the Connection panel see section 4 14 2 for details If none of the settings here seems to help you may find question A 7 15 to be useful 4 4 1 Changing the action of the Backspace key Some terminals believe that the Backspace key should send the same thing to the server as Control H ASCII code 8 Other terminals believe that the Backspace key should send ASCII code 127 usually k T nown as Control so that it can be distinguished from Control H his option allows you to choose which code PuTTY generates when you press Backspace If you are connecting over SSH PuTTY by default tells the server the value of this option see section 4 21 2 so you may find that the Backspace key does the right thing either way Similarly if you are connecting to a Unix system you will probably find that the Unix stty command lets you configure which the server expects t g a o see so again you might not need to change which one PuTTY enerates On other systems the server s expectation might be fixed nd you might have no choice but to configure PuTTY If you do have the choice we recommend configuring PuTTY to generate Control and configuring the server to expect it because that allows applications such as emacs to use Control H for help Typing Shift Backspace will cause PuTTY to send whichever code isn t configured here as the defau
171. les PSFTP allows you to modify the file permissions on files and directories on the server You do this using the chmod command which works very much like the Unix chmod command The basic syntax is chmod modes file where modes represents a modification to the file permissions and file is the filename to modify You can specify multiple files or wildcards For example chmod go rwx utw privatefile chmod atr public chmod 640 groupfilel groupfile2 The modes style modifications parameter can be a set of octal digits i If you don t know what this means to be using it n the Unix you probably don t want Alternatively it can be a list of permission separated by commas Each modification consists of The peopl the owning user everybody else can also be A Tor added or removed p affected by the modification This can be u g members of the owning group or o others or some combination of those It a all to affect everybody at once sign indicating whether permissions are to be The actual permissions being added or removed These can be permission to read the file w permission to write to the file and x permission to execute the file or in the case of a directory directory permission to access files within the 7 11 2008 6 2 15 6 2 16 62 17 Page 73 of 131 So the abov xamples would do
172. les are transferred instead remote files are listed Only a hostname specification and optional remote file specification need be given For example pscp ls fred example com dirl The SCP protocol does not contain within itself a means of listing files If SCP is in use this option therefore assumes that the server responds appropriately to the command ls la this may not work with all servers If SFTP is in use this option should work with all servers 5 2 2 2 p preserve file attributes By default files copied with PSCP are timestamped with the date and time they were copied The p option preserves the original timestamp on copied files 5 2 2 3 q quiet don t show statistics By default PSCP displays a meter displaying the progress of the current transfer mibs tar 168 kB 84 0 kB s ETA 00 00 13 13 The fields in this display are from left to right filename size in kilobytes of file transferred so far estimate of how fast the file is being transferred in kilobytes per second estimated time that the transfer will be complete and percentage of the file so far transferred The q option to PSCP suppresses the printing of these statistics 5 2 2 4 r copies directories recursively By default PSCP will only copy files Any directories you specify to copy will be skipped as will their contents The r option tells PSCP to descend into any directories
173. line at a time locally and the line will only be sent to the server when you press Return If you make a mistake you can use the Backspace key to correct it before you press Return and the server will never see the mistake Since it is hard to edit a line locally without being able to see it local line editing is mostly used in conjunction with local echo section 4 3 7 This makes it ideal for use in raw mode or when connecting to MUDs or talkers Although some more advanced MUDs do occasionally turn local line editing on and turn local echo off in order to accept a password from the user Some types of session need local line editing and many do not In its default mode PuTTY will automatically attempt to deduce whether or not local line editing is appropriate for the session you are working in If you find it has made the wrong decision you can use this configuration option to override its choice you can force local line editing to be turned on or force it to be turned off instead of relying on the automatic detection 4 3 9 Remote controlled printing A lot of VT100 compatible terminals support printing under control of the remote server PuTTY supports this feature as well but it is turned off by default http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 25 of 131 To enable remote controlled printing choose a printer from the Printer to send
174. line to use if your computer has more than one and what speed baud rate to use when transferring data For further configuration options data bits stop bits parity flow control you can use the Serial configuration panel see section 4 25 After you start up PuTTY in serial mode you might find that you have to make the first move by sending some data out of the serial line in order to notify the device at the other end that someone is there for it to talk to This probably depends on the device If you start up a PuTTY serial session and nothing appears in the window try pressing Return a few times and see if that helps A serial line provides no well defined means for one end of the connection to notify the other that the connection is finished Therefore PuTTY in serial mode will remain connected until you close the window using the close button 3 8 The PuTTY command line PuTTY can be made to do various things without user intervention by supplying command line arguments e g from a command prompt window or a Windows shortcut 3 8 1 Starting a session from the command line These options allow you to bypass the configuration window and launch straight into a session To start a connection to a server called host putty exe ssh telnet rlogin raw user host If this syntax is used settings are taken from the Default Settings see section 4 1 2 user overrides these settin
175. ll save the resulting file as filename dat in your local working directory To change your local working directory use the lcd command To display your current local working directory type lpwd 6 2 9 The get command fetch a file from the server To download a file from the server and store it on your local PC you use the get command In its simplest form you just use this with a file name get myfile dat If you want to store the file locally under a different name specify the local file name after the remote on get myfile dat newname dat This will fetch the file on the server called myfile dat but will save it to your local machine under the name newname dat To fetch an entire directory recursively you can use the r option get r mydir http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 71 of 131 get r mydir newname If you want to fetch a file whose name starts with a hyphen you may have to use the special argument which stops get from interpreting anything as a switch after it For example get silly name 6 2 10 The put command send a file to the server To upload a file to the server from your local PC you use the put command In its simplest form you just use this with a file name put myfile dat If you want to store the file remotely under a different name specify the remote file name after t
176. lling to sign something for you without it setting such a precedent If your company policy requires you to have an individual agreement with the supplier of any software you use then your company policy is simply not well suited to using popular free software and we urge you to consider this as a flaw in your policy If you won t sign anything can you give us some sort of assurance that you won t make PuTTY closed source in future Yes and no If what you want is an assurance that some _current version_ of PuTTY which you ve already downloaded will remain free then you already have that assurance it s called the PuTTY Licence It grants you permission to use distribute and copy the software to which it applies once we ve granted that permission which we have we can t just revoke it On the other hand if you want an assurance that _future_ versions of PuTTY won t be closed source that s more difficult We could in principle sign a document stating that we would never release a closed source PuTTY but that wouldn t assure you that we _would_ keep releasing _open_ source PuTTYs we would still have the option of ceasing to develop PuTTY at all which would surely be even worse for you than making it closed source And we almost certainly wouldn t _want_ to sign a document guaranteeing that we would actually continue to do development work on PuTTY we certainly wouldn t sign it for free Documents like that are called
177. lly does make _that_ much differenc e If you re having a specific problem with host key checking perhaps you want an automated batch job to make use of PSCP or Plink and the interactive host key prompt is hanging the batch process then the right way to fix it is to add the correct host key to the Registry in advance That way you retain the _impo rtant_ feature of host key checking the right key will be accepted and the wrong ones urn host key checking off completely will not Adding an option to t is the wrong solution and we wi If you have host keys available we have a script called kh2reg FL mot do ET in the common known_hosts format py to convert them to a Windows REG file which can be installed ahead of time by double clicking or using REGEDIT A 2 10 Will you write an SSH server fo client No The only reason we might wa r the PuTTY suite to go with the nt to would be if we could easily re use existing code and significantly cut down the effort We don t just isn t enough common ground between an SSH client and server to make it worthwhile believe this is the case ther If someone else wants to use bi ts of PuTTY in the process of writing a Windows SSH server they d b I really can t see it being a perfectly welcome to of course but ot less effort for us to do that than it would be for us to write a serv
178. login Once logged in you must configure the server to accept your public key for authentication If your server is using the SSH 1 protocol you should change into the ssh directory and open the file authorized_keys with your favourite editor You may have to create this file if this is the first key you have put in it Then switch to the PuTTYgen window select all of the text in the Public key for pasting into authorized_keys file box see section 8 2 10 and copy it to the clipboard Ctrl C Then switch back to the PuTTY window and insert the data into the open file making sure it ends up all on one line Save the fil If your server is OpenSSH and is using the SSH 2 protocol you should follow the same instructions except that in earlier versions of OpenSSH 2 the file might be called authorized_keys2 In modern versions the same authorized_keys file is used for both SSH 1 and SSH 2 keys If your server is ssh com s product and is using SSH 2 you need to save a _public_ key file from PuTTYgen see section 8 2 9 and copy that into the ssh2 directory on the server Then you should go into that ssh2 directory and edit or create a file called authorization In this file you should put a line like Key mykey pub with mykey pub replaced by the name of your key file For other SSH server software you should refer to the manual for that server Y
179. login username All three of the SSH Telnet and Rlogin protocols allow you to specify what user name you want to log in as without having to type it explicitly every time Some Telnet servers don t support this In this box you can type that user name 4 14 2 Terminal type string Most servers you might connect to with PuTTY are designed to be connected to from lots of different types of terminal In order to send the right control sequences to each one the server will need to know what type of terminal it is dealing with Therefore each of the SSH Telnet and Rlogin protocols allow a text string to be sent down the connection describing the terminal On a Unix server this selects an entry from the termcap or terminfo database that tells applications what control sequences to send to the terminal and what character sequences to expect the keyboard to generate PuTTY attempts to emulate the Unix xterm program and by default it reflects this by sending xterm as a terminal type string If you find this is not doing what you want perhaps the remote system reports Unknown terminal type you could try setting this to something different such as vt220 If you re not sure whether a problem is due to the terminal type setting or not you probably need to consult the manual for your application or your server 4 14 3 Terminal speeds he Telnet Rlogin and SSH pr
180. lt 4 4 2 Changing the action of the Home and End keys The Unix terminal emulator rxvt disagrees with the rest of the world about what character sequences should be sent to the server by the Home and End keys http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 26 of 131 xterm and other terminals send ESC 1 for the Home key and ESC 4 for the End key rxvt sends ESC H for the Home key and ESC Ow for the End key If you find an application on which the Home and End keys aren t working you could try switching this option to see if it helps 4 4 3 Changing the action of the function keys and keypad This option affects the function keys F1 to F12 and the top row of the numeric keypad In the default mode labelled ESC n the function keys generate sequences like ESC 11 ESC 12 and so on This matches the general behaviour of Digital s terminals In Linux mode F6 to F12 behave just like the default mode but Fl to F5 generate ESC A through to ESC E This mimics the Linux virtual console In Xterm R6 mode F5 to F12 behave like the default mode but Fl to F4 generate ESC OP through to ESC OS which are the sequences produced by the top row of the _keypad_ on Digital s terminals H n VT400 mode all the function keys behave like the default mode but the actua
181. ly what problem it had with your setup 10 10 Access denied Authentication refused Various forms of this error are printed in the PuTTY window http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 93 of 131 or written to the PuTTY Event Log see section 3 1 3 1 during authentication If you see one of these messages it means that the server has refused all the forms of authentication PuTTY has tried and it has no further ideas It may be worth checking the Event Log for diagnostic messages from the server giving more detail This error can be caused by buggy SSH 1 servers that fail to cope with the various strategies we use for camouflaging passwords in transit Upgrade your server or use the workarounds described in section 4 24 1 and possibly section 4 24 2 10 11 Incorrect CRC received on packet or Incorrect MAC received on packet This error occurs when PuTTY decrypts an SSH packet and its checksum is not correct This probably means something has gone wrong in the encryption or decryption process It s difficult to tell from this error message whether the problem is in the client in the server or in between A known server problem which can cause this error is described in question A 7 16 in the FAQ 10 12 Incoming packet was garbled on decryption This error occurs when PuTTY decrypts an SSH packet and the decrypted data makes no sense This probably mea
182. ly_ copied to the clipboard You do not need to press Ctrl C or Ctrl Ins in fact if you do press Ctrl C PuTTY will send a Ctrl C character down your session to the server where it will probably cause a process to be interrupted Pasting is done using the right button or the middle mouse button if you have a three button mouse and have set it up see section 4 11 2 Pressing Shift Ins or selecting Paste from the Ctrl right click context menu have the sam ffect When you click the right mouse button PuTTY will read whatever is in the Windows clipboard and paste it into your session _exactly_ as if it had been typed at the keyboard Therefore be careful of pasting formatted text into an editor that does automatic indenting you may find that the spaces pasted from the clipboard plus the spaces added by the editor add up to too many spaces and ruin the formatting There is nothing PuTTY can do about this If you double click the left mouse button PuTTY will select a whole word If you double click hold down the second click and drag the mouse PuTTY will select a sequence of whole words You can adjust precisely what PuTTY considers to be part of a word see section 4 11 5 If you _triple_ click or triple click and drag then PuTTY will select a whole line or sequence of lines If you want to select a rectangular region instead of selecting to the end of each line you can do this by holding
183. malicious attacker redirects your connection to ano If you see this message key before and You should attempt to verify the host asking the machine s administrator key by other If you see this message and you know that your installation of PuTTY it may have been recently to th server before _has_ connected sam it means that PuTTY has no has no way of knowing whether it is ther machine t seen this host correct or not means such as upgraded to SSH protocol version 2 SSH protocols 1 and 2 use separate host keys have only used SSH 1 with before so when you first use SSH 2 with a server you you will see this message again You should verify the correctness of the key as before See section 2 2 for more information on host keys WARNING POTENTIAL SECURITY BREACH This message the one PuTTY has cached in the registry connected to the SSH server before knows what its be but has found a different one This may mean with a different one to their own machine On the other hand it may followed by The server s host key does not match means that PuTTY has host key _should_ that a malicious attacker has replaced your server or has redirected your network connection simply mean that the administrator of your server has accidentally changed the key while upgrading the SSH software unfortunately possible You should contact your server s administrato
184. me fred Remote working directory is home fred Listing directory home fred lib drwxrwsr x 4 fred fred 1024 Sep 6 10 42 drwxr Ssr x 25 fred fred 2048 Dec 14 09 36 drwxrwsr x 3 fred fred 1024 Apr 17 2000 jed lrwxrwxrwx 1 fred fred 24 Apr 17 2000 timber drwxrwsr x 2 fred fred 1024 Mar 13 2000 trn you might see this C gt psftp fred hostname bc b batchfile Sent username fred Remote working directory is home fred http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 6 ee abe 23 3 g2 Page 68 of 131 psftp gt dir lib Listing directory home fred lib drwxrwsr x 4 fred fred 1024 Sep 6 10 42 drwxr Sr x 25 fred fred 2048 Dec 14 09 36 drwxrwsr x 3 fred fred 1024 Apr 17 2000 jed lrwxrwxrwx 1 fred fred 24 Apr 17 2000 timber drwxrwsr x 2 fred fred 1024 Mar 13 2000 trn psftp gt quit be continue batch processing on errors When running a batch file this additional option causes PSFTP to continue processing even if a command fails to complete successfully You might want this to happen if you wanted to delete a file and didn t care if it was already not present for example batch avoid interactive prompts If you use the batch option PSFTP will never give an interactive prompt while establishing the connection If the server s host key is invalid for exampl s section 2 2 then the connection will simply be abandoned instead of asking you what to do next
185. mmunicator series is available from http s2putty sourceforge net Embedding PuTTY in other programs Is the SSH or Telnet code available as a DLL No it isn t It would take a reasonable amount of rewriting for this to be possible and since the PuTTY project itself doesn t believe in DLLs they make installation mor rror prone none of us has taken the time to do it Most of the code cleanup work would be a good thing to happen in general so if anyone feels like helping we wouldn t say no Is the SSH or Telnet code available as a Visual Basic component No it isn t None of the PuTTY team uses Visual Basic and none of us has any particular need to make SSH connections from a Visual Basic application In addition all the preliminary work to turn it into a DLL would be necessary first and furthermore we don t even know how to write VB components If someone offers to do some of this work for us we might consider it but unless that happens I can t see VB integration being anywhere other than the very bottom of our priority list How can I use PuTTY to make an SSH connection from within another program Probably your best bet is to use Plink the command line connection tool If you can start Plink as a second Windows process and arrange for your primary process to be able to send data to the Plink process and receive data from it through pipes then you should be able to make SSH connections from y
186. mon user error in a terminal session is to accidentally run the Unix command cat or equivalent on an inappropriate file type such as an executable image file or ZIP file This produces a huge stream of non text characters sent to the terminal which typically includes a lot of bell characters As a result of this the terminal often doesn t stop beeping for ten minutes and everybody else in the office gets annoyed To try to avoid this behaviour or any other cause of excessiv beeping PuTTY includes a bell overload management feature In the default configuration receiving more than five bell characters in a two second period will cause the overload feature to activate Once the overload feature is active further bells will have no effect at all so the rest of your binary file will be sent to the screen in silence After a period of five seconds during which no further bells are received the overload feature will turn itself off again and bells will be re enabled If you want this feature completely disabled you can turn it off using the checkbox Bell is temporarily disabled when over used Alternatively if you like the bell overload feature but don t agree with the settings you can configure the details how many bells constitute an overload how short a time period they have to arrive in to do so and how much silent time is required before th overload feature wil
187. money we won t argue Th asiest way for us to accept donations is if http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 113 of 131 you send money to lt anakin pobox com gt using PayPal www paypal com Alternatively if you don t trust PayPal you could donate through e gold www e gold com deposit your donation in account number 174769 then send us e mail to let us know you ve done so otherwise we might not notice for months Small donations tens of dollars or tens of euros will probably be spent on beer or curry which helps motivate our volunteer team to continue doing this for the world Larger donations will be spent on something that actually helps development if we can find anything perhaps new hardware or a copy of Windows XP but if we can t find anything then we ll just distribute the money among the developers If you want to be sure your donation is going towards something worthwhile ask us first If you don t like these terms feel perfectly free not to donate We don t mind A 9 8 Can I have permission to put PuTTY on a cover disk distribute it with other software etc Yes For most things you need not bother asking us explicitly for permission our licence already grants you permission See section B 7 for more details A 9 9 Can you sign an agreement indemnifying us against security problems in PuTTY No A vendor of physical security products e g
188. n box it will be ignored This will cause PuTTY to listen on the port you have specified and provide a SOCKS proxy service to any programs which connect to that port So in particular you can forward other PuTTY connections through it by setting up the Proxy control panel see section 4 15 for details The source port for a forwarded connection usually does not accept connections from any machine except the SSH client or server machine itself for local and remote forwardings respectively There are controls in the Tunnels panel to change this The Local ports accept connections from other hosts option allows you to set up local to remote port forwardings including dynamic port forwardings in such a way that machines other than your client PC can connect to the forwarded port The Remote ports do the same option does the same thing for remote to local port forwardings so that machines other than the SSH server machine can connect to the forwarded port Note that this feature is only available in the SSH 2 protocol and not all SSH 2 servers honour it in OpenSSH for example it s usually disabled by default You can also specify an IP address to listen on Typically a Windows machine can be asked to listen on any single IP address in the 127 range and all of these are loopback addresses available only to the local machine So if you forward for example 127 0 0 5 79 to a r
189. n easily happen if you are using Pageant and have a large number of keys loaded into it since these servers count each offer of a public key as an authentication attempt This can be worked around by specifying the key that s required for the authentication in the PuTTY configuration see section 4 20 7 PuTTY will ignore any other keys Pageant may have but will ask Pageant to do the authentication so that you don t have to type your passphrase On the server this can be worked around by disabling public key authentication or for Sun SSH only by increasing MaxAuthTries in sshd_config 10 6 Out of memory This occurs when PuTTY tries to allocate more memory than the system can give it This _may_ happen for genuine reasons if the computer really has run out of memory or if you have configured an extremely large number of lines of scrollback in your terminal PuTTY is not able to recover from running out of memory it will terminate immediately after giving this error However this error can also occur when memory is not running out at all because PuTTY receives data in the wrong format In SSH 2 and also in SFTP the server sends the length of each message before th message itself so PuTTY will receive the length try to allocate space for the message and then receive the rest of the message If the length PuTTY receives is garbage it will try to allocate a ridiculous amount of memory and will terminate
190. n t show statistics E copy directories recursively v show verbose messages load sessname Load settings from saved session P port connect to specified port l user connect with specified usernam pw passw login with specified password 2 force use of particular SSH protocol version 4 6 force use of IPv4 or IPv6 enable compression i key private key file for authentication noagent disable use of Pageant agent enable use of Pageant batch disable all interactive prompts unsafe allow server side wildcards DANGEROUS sftp force use of SFTP protocol scp force use of SCP protocol PSCP s interface is much like the Unix scp command if you re familiar with that The basics To receive a file s from a remote server pscp options user host source target So to copy the file etc hosts from the server example com as user fred to the file c temp example hosts txt you would type pscp fred example com etc hosts c temp example hosts txt To send a file s to a remote server pscp options source source user host target So to copy the local file c documents foo txt to the server example com as user fred to the file tmp foo you would type pscp c documents foo txt fred example com tmp foo You can use wildcards to transfer multiple files in either direction like this pscp c documents doc fred example com docfiles pscp fred example com
191. n the session name in the list box To delete a saved session single click to select the session name in the list box and then press the Delete button saved session is independent of the Default Settings iguration If you change your preferences and update Default ings you must also update every saved session separately d sessions are stored in the Registry at the location EY_CURRENT_USER Software SimonTatham PuTTY Sessions ou need to store them in a file you could try the method ribed in section 4 26 se Window on Exit lly in the Session panel there is an option labelled Close ow on Exit This controls whether the PuTTY terminal window ppears as soon as the session inside it terminates If you are ly to want to copy and paste text out of the session after it terminated or restart the session you should arrange for this on to be off se Window On Exit has three settings Always means always e the window on exit Never means never close on exit always e the window open but inactive The third setting and the ult one is Only on clean exit In this mode a session which inates normally will cause its window to close but one which is ted unexpectedly by network trouble or a confusing message from server will leave the window up http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 20 of 131 4 2 The Logging panel N s t
192. nces to get it right If you are using SSH be careful not to type your username wrongly because you will not have a chance to correct it after you press Return many SSH servers do not permit you to make two login attempts using different usernames If you type your username wrongly you must close PuTTY and start again If your password is refused but you are sure you have typed it correctly check that Caps Lock is not enabled Many login servers particularly Unix computers treat upper case and lower case as different when checking your password so if Caps Lock is on your password will probably be refused 2 4 After logging in After you log in to the server what happens next is up to the server Most servers will print some sort of login message and then present a prompt at which you can type commands which the server will carry out Some servers will offer you on line help others might not If you are in doubt about what to do next consult your system administrator 2 5 Logging out When you have finished your session you should log out by typing the server s own logout command This might vary between servers if in doubt try logout or exit or consult a manual or your system administrator When the server processes your logout command the PuTTY window should close itself automatically You _can_ close a PuTTY session using the Close button in the window border but this might confuse the se
193. nd set it as Run Maximized A 6 4 How can I create a Windows shortcut to start a particular saved session directly To run a PuTTY session saved under the name mysession create a Windows shortcut that invokes PuTTY with a command line like path name to putty exe load mysession Note prior to 0 53 the syntax was session This is now deprecated and may be removed at some point A 6 5 How can I start an SSH session straight from the command line Use the command line putty ssh host name Alternatively create a saved session that specifies the SSH protocol and start the saved session as shown in question A 6 4 A 6 6 How do I copy and paste between PuTTY and other Windows applications Copy and paste works similarly to the X Window System You use the left mouse button to select text in the PuTTY window The act of selection _automatically_ copies the text to the clipboard there is no need to press Ctrl Ins or Ctrl C or anything else In fact pressing Ctrl C will send a Ctrl C character to the other end of your connection just like it does the rest of the time which may have unpleasant effects The _only_ thing you need to do to copy text to the clipboard is to select it To paste the clipboard contents into a PuTTY window by default you click the right mouse button If you have a three button mouse and are used to X applications you can configure pasting to be done by the middle button ins
194. newn and sresize macros explicitly cast the return values of malloc and realloc to the target type This has type checking advantages even in C it means http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 125 of 131 you never accidentally allocate the wrong size piece of memory for the pointer type you re assigning it to C friendliness is really a side benefit We want PuTTY to continue being pure C at least in the platform independent parts and the currently existing ports Patches which switch the Makefiles to compile it as C and start using classes will not be accepted Also in particular we disapprove of comments at least for the moment Perhaps once C99 becomes genuinely widespread we might be more lenient The one exception a port to a new platform may use languages other than C if they are necessary to code on that platform If your favourite PDA has a GUI with a C API then there s no way you can do a port of PuTTY without using C so go ahead and use it But keep the C restricted to that platform s subdirectory if your changes force the Unix or Windows ports to be compiled as C they will be unacceptable to us D 5 Security conscious coding PuTTY is a network application and a security application Assume your code will end up being fed deliberately malicious data by attackers and try to code in a way that makes it unlikely to be a security
195. ng to do is to edit Recipe and re run mkfiles pl This will cause the new object file to be added in every tool that http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 LZ 3 http the earth li sgtatham putty 0 60 puttydoc txt Page 128 of 131 requires it on every platform where it matters in every Makefile to which it is relevant _and_ to get all the dependency data right If you send us a patch that modifies one of the Makefiles you just waste our time because we will have to convert it into a change to Recipe If you send us a patch that modifies _all_ of the Makefiles you will have wasted a lot of _your_ time as well There is a comment at the top of every Makefile in the PuTTY source archive saying this but many people don t seem to read it so it s worth repeating here Coroutines in ssh c Large parts of the code in ssh c are structured using a set of macros that implement something close to Donald Knuth s coroutines concept in C Essentially the purpose of these macros are to arrange that a function can call crReturn to return to its caller and the next time it is called control will resume from just after that crReturn statement This means that any local automatic variables declared in such a function will be corrupted every time you call crReturn If you need a variable to persist for longer than that you _must_ make it a field in
196. ng trouble with a firewall passive mode to s if it helps you could try enabling Keyboard sends Telnet special commands If this box is checked actions modified several key sequences will have their normal the Backspace key on the keyboard will send th backspace code Telnet special Control C will send the Tel net special Interrupt Process code Control Z will send the Tel net special Suspend Process code You probably shouldn t enable t doing his unless you know what you re Return key sends Telnet New Line instead of M Unlike most ot a special new endings of Con Telnet New Lin Control M as it her remote login protocols line trol M cod does the Telnet protocol has code that is not the same as the usual line or Control J By default PuTTY sends the when you press Return instead of sending in most other protocols 7 11 2008 Page 47 of 131 Most Unix style Telnet servers don t mind whether they receiv Telnet New Line or Control M some servers do expect New Line and some servers prefer to see M If you are seeing surprising behaviour when you press Return in a Telnet session you might try turning this option off to see if it helps 4 17 The Rlogin panel he Rlogin panel allows you to configure options that only apply to Rlogin sessions 4 17 1 Local username Rlogin allows
197. nk Thus server side software that expects a response is kept happy but an attacker cannot influence the response string This is probably the setting you want if you have no better ideas http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 31 of 131 Window title PuTTY responds with the actual window title This is dangerous for the reasons described above 4 6 7 Disabling destructive backspace Normally when PuTTY receives character 127 from the server it will perform a destructive backspace move the cursor one space left and delete the character under it This can apparently cause problems in some applications so PuTTY provides the ability to configure character 127 to perform a normal backspace without deleting a character instead 4 6 8 Disabling remote character set configuration PuTTY has the ability to change its character set configuration in response to commands from the server Some programs send these commands unexpectedly or inconveniently In particular an IRC client seems to have a habit of reconfiguring the character set to something other than the user intended If you find that accented characters are not showing up the way you expect them to particularly if you re running BitchX you could try disabling the remote character set configuration commands 4 6 9 Disabling Arabic text shaping PuTTY supports shaping of Arabic text which means that i
198. ns of PuTTY automatically initiate repeat key exchange once per hour to improve session security If your client or server machine is slow you may experience this as a delay of anything up to thirty seconds or so These delays are inconvenient but they are there for your protection If they really cause you a problem you can choose to turn off periodic rekeying using the Kex configuration panel see section 4 19 but be aware that you will be sacrificing security for this Falling back to SSH 1 would also remove the delays but would lose a _lot_ more security still We do not recommend it A 7 24 PuTTY fails to start up Windows claims that the application configuration is incorrect This is caused by a bug in certain versions of Windows XP which is triggered by PuTTY 0 58 This was fixed in 0 59 The xp wont run entry in PuTTY s wishlist has more details A 8 Security questions A 8 1 Is it safe for me to download PuTTY and use it on a public PC It depends on whether you trust that PC If you don t trust the public PC don t use PuTTY on it and don t use any other software you plan to type passwords into either It might be watching your keystrokes or it might tamper with the PuTTY binary you download There is _no_ program safe enough that you can run it on an actively malicious PC and get away with typing passwords into it If you do trust the PC then it s probably OK to use PuTTY on it but if you
199. ns something has gone wrong in the encryption or decryption process It s difficult to tell from this error message whether the problem is in the client in the server or in between If you get this error one thing you could try would be to fiddle with the setting of Miscomputes SSH 2 encryption keys on the Bugs panel see section 4 24 5 Another known server problem which can cause this error is described in question A 7 16 in the FAQ 10 13 PuTTY X11 proxy _various errors_ his family of errors are reported when PuTTY is doing X forwarding hey are sent back to the X application running on the SSH server which will usually report the error to the user When PuTTY enables X forwarding see section 3 4 it creates a virtual X display running on the SSH server This display requires authentication to connect to it this is how PuTTY prevents other users on your server machine from connecting through the PuTTY proxy to your real X display PuTTY also sends the server the details it needs to enable clients to connect and the server should put this mechanism in place automatically so your X applications should just work A common reason why people s one of these messages is because they used SSH to log in as one user let s say fred and then used the Unix su command to become another user typically root The original user fred has access to the X authentication data provide
200. ns w browser links he server to send control codes that let it take and use it for purposes other than copy and paste hich use this feature include the text mode web the Usenet newsreader trn version 4 and the file manager mc Midnight Commander When running o ne of these applications pressing the mouse buttons no longer performs copy and paste If you do need to copy and paste you can still do so if you hold down Shift while you do your mouse clicks However it is possible in theory for applications to even detect and make use of Shift mouse clicks We don t know of any applications that do this but in case someon ver writes one unchecking the Shift overrides application s use of mouse checkbox will cause Shift mouse clicks to go to the server as well so that mouse driven copy and paste will be completely disabled If you want to prevent the application from taking over the mouse at all you can do this using the Features control panel see section 4 6 2 4 11 4 Default selection mode http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 38 of 131 As described in section 3 1 1 PuTTY has two modes of selecting text to be copied to the clipboard In the default mode Normal dragging the mouse from point A to point B selects to the end of the line containing A all the lines in between and from the very beginning of the line con
201. ntil you load a private key into it If you click the Pageant icon with the right mouse button you will S a menu Select View Keys from this menu The Pageant main window will appear You can also bring this window up by double clicking on the Pageant icon The Pageant window contains a list box This shows the private keys Pageant is holding When you start Pageant it has no keys so the list box will be empty After you add one or more keys they will show up in the list box To add a key to Pageant press the Add Key button Pageant will bring up a file dialog labelled Select Private Key File Find your private key file in this dialog and press Open Pageant will now load the private key If the key is protected by a passphrase Pageant will ask you to type the passphrase When the key has been loaded it will appear in the list in the Pageant window Now start PuTTY and open an SSH session to a site that accepts your key PuTTY will notice that Pageant is running retrieve the key automatically from Pageant and use it to authenticate You can now open as many PuTTY sessions as you like without having to type your passphrase again PuTTY can be configured not to try to use Pageant but it will try by default See section 4 20 2 and section 3 8 3 9 for more information When you want to shut down Pageant click the right button on the Pageant icon in the System tray and select Ex
202. o find you need to disable Arabic text shaping see section 4 6 9 http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 32 of 131 4 7 The Window panel The Window configuration panel allows you to control aspects of the PuTTY window 4 7 1 Setting the size of the PuTTY window The Columns and Rows boxes let you set the PuTTY window to a precise size Of course you can also drag the window to a new size while a session is running 4 7 2 What to do when the window is resized 4 J here are four options here These options allow you to control what happens when th to resize the PuTTY window using its window furniture user tries Change the number of rows and columns the font size will not change This is the default Change the size of the font the number of rows and columns in the terminal will stay the same and the font size will change Change font size when maximised when the window is resized the number of rows and columns will change _except_ when the window is maximised or restored when the font size will change resized at all 4 7 3 Controlling scrollback 3 These options let you configure scrolls off the top of the scr Forbid resizing completely the terminal will refuse to be the way PuTTY keeps text after it n s section 3 1 2 he Lines of scrollback box le text PuTTY keeps the scrollbar altho
203. ogin account This might also be known as a _shell account_ _shell_ is the program that runs on the server and interprets 7 11 2008 Page 2 of 131 you want to use a bulletin board system talker or MUD which can be accessed using Telnet You probably do _not_ want to use SSH Telnet or Rlogin if you only use Windows Windows computers have their own ways of networking between themselves and unless you are doing something fairly unusual you will not need to use any of these remote login protocols 1 2 How do SSH Telnet and Rlogin differ This list summarises some of the differences between SSH Telnet and Rlogin SSH which stands for secure shell is a recently designed high security protocol It uses strong cryptography to protect your connection against eavesdropping hijacking and other attacks Telnet and Rlogin are both older protocols offering minimal security SSH and Rlogin both allow you to log in to the server without having to type a password Rlogin s method of doing this is insecure and can allow an attacker to access your account on the server SSH s method is much more secure and typically breaking the security requires the attacker to have gained access to your actual client machine SSH allows you to connect to the server and automatically send a command so that the server will run that command and then disconnect So you can use it in automated processing The Internet is a
204. ol panel that comes up before you start a session Some options can also be changed in the middle of a session by selecting Change Settings from the window menu 4 1 The Session panel The Session configuration panel contains the basic options you need to specify in order to open a session at all and also allows you to save your settings to be reloaded later 4 1 1 The host name section The top box on the Session panel labelled Specify your connection by host name contains the details that need to be filled in before PuTTY can open a session at all The Host Name box is where you type the name or the IP address of the server you want to connect to The Connection type radio buttons let you choose what type of connection you want to make a raw connection a Telnet connection an Rlogin connection an SSH connection or a connection to a local serial line See section 1 2 fora summary of the differences between SSH Telnet and rlogin see section 3 6 for an explanation of raw connections see section 3 7 for information about using a serial line he Port box lets you specify which port number on the server o connect to If you select Telnet Rlogin or SSH this box ill be filled in automatically to the usual value and you will nly need to change it if you have an unusual server If you elect Raw mode you will almost certainly need to fill in the Port box yourself If y
205. on of a second Beep using the PC speaker is self explanatory Play a custom sound file allows you to specify a particular sound file to be used by PuTTY alone or even by a particular individual PuTTY session This allows you to distinguish your PuTTY beeps from any other beeps on the system If you select this option you will also need to ent file in the edit control Custom sound 4 5 2 Taskbar caption indication on bell r the name of your sound file to play as a bell This feature controls what happens to the PuTTY window s entry in the Windows Taskbar if a bell occurs while the input focus the window does not have In the default state Disabled nothing unusual happens If you select Steady then when a bell occurs and the window is not in focus the window s Taskbar entry and its title bar will change colour to let you know that PuTTY session is asking for your attention The change of colour will persist until you select the window so you can leave several PuTTY windows minimised in your terminal go away from your keyboard and be sure not to have missed any important beeps when you get back Flashing is even mor ye catching the continuously flash on and off until you sel http the earth li sgtatham putty 0 60 puttydoc txt Taskbar entry will lect the window 7 11 2008 Page 29 of 131 4 5 3 Control the bell overload behaviour A com
206. on or you re simply curious you can turn this switch on and hope to find out more about what is happening 3 8 3 4 l specify a login name You can specify the user name to log in as on the remote server using the 1 option For example plink login example com i fred These options are equivalent to the username selection box in the Connection panel of the PuTTY configuration box see section 4 14 1 3 8 3 5 L R and D set up port forwardings As well as setting up port forwardings in the PuTTY configuration see section 4 23 you can also set up forwardings on the command line The command line options work just like the ones in Unix ssh programs To forward a local port say 5110 to a remote destination say popserver example com port 110 you can write something like one of these putty L 5110 popserver example com 110 load mysession plink mysession L 5110 popserver example com 110 To forward a remote port to a local destination just use the R option instead of L putty R 5023 mytelnetserver myhouse org 23 load mysession plink mysession R 5023 mytelnetserver myhouse org 23 To specify an IP address for the listening end of the tunnel prepend it to the argument plink L 127 0 0 5 23 localhost 23 myhost To set up SOCKS based dynamic port forwarding on a local port use the D option For this one you only have to pass the port number putty
207. on you can go back to the Logging panel and select Logging turned off completely to stop logging then PuTTY will close the log file and you can safely read it See section 4 2 for more details and options 3 3 Altering your character set configuration If you find that special characters accented characters for example or line drawing characters are not being displayed correctly in your PuTTY session it may be that PuTTY is interpreting the characters sent by the server according to the wrong _character set_ There are a lot of different character sets available so it s entirely possible for this to happen If you click Change Settings and look at the Translation panel you should see a large number of character sets which you can select and other related options Now all you need is to find out which of them you want See section 4 10 for more information 3 4 Using X11 forwarding in SSH he SSH protocol has the ability to securely forward X Window System ppelications over your encrypted SSH connection so that you can run n application on the SSH server machine and have it put its windows p on your local machine without sending any X network traffic in he clear to oo H In order to use this feature you will need an X display server for your Windows machine such as Cygwin X X Win32 or Exceed This will probably install itself as display number 0 on your local m WwW
208. onsole window With Windows 95 98 and ME this is called an MS DOS Prompt and with Windows NT 2000 and XP it is called a Command Prompt It should be available from the Programs section of your Start Menu To start PSCP it will need either to be on your PATH or in your current directory To add the directory containing PSCP to your PATH environment variable type into the console window set PATH C path to putty directory sPATHS This will only work for the lifetime of that particular console window To set your PATH more permanently on Windows NT 2000 and XP use the Environment tab of the System Control Panel On Windows 95 98 and ME you will need to edit your AUTOEXEC BAT to include a set command like the one abov PSCP Usage Once you ve got a console window to type into you can just type pscp on its own to bring up a usage message This tells you the http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 aoe Page 62 of 131 version of PSCP you re using and gives you a brief summary of how to use PSCP Z owendadmin gt pscp PuTTY Secure Copy client Release 0 60 Usage pscp options user host source target pscp options source source user Jhost target pscp options ls user Jhost filespec Options V print version information and exit pgpfp print PGP key fingerprints and exit p preserve file attributes quiet do
209. ority Check the Wishlist and Change snapshots If it isn t clear snapshot and see if the featu Log on the PuTTY website and s if we have already added your feature in the development download the latest re is present If it http the earth li sgtatham putty 0 60 puttydoc txt development is then it 7 11 2008 Page 120 of 131 will also be in the next release and there is no need to mail us at all If you can t find your feature in either the development snapshots _or_ the Wishlist then you probably do need to submit a feature request Since the PuTTY authors are very busy it helps if you try to do some of the work for us Do as much of the design as you can Think about corner cases think about how your feature interacts with other existing features Think about the user interface if you can t come up with a simple and intuitive interface to your feature you shouldn t be surprised if we can t either Always imagine whether it s possible for there to be more than one or less than one of something you d assumed there would be one of For example if you were to want PuTTY to put an icon in the System tray rather than the Taskbar you should think about what happens if there s more than one PuTTY active how would the user tell which was which If you can program it may be worth offering to write the feature yourself and send us a patch However it is likely to be helpf
210. ot be configured within PuTTY If the operating system does not receive a response to a keepalive it may send out more in quick succession and terminate the connection if no response is received CP keepalives may be more useful for ensuring that half open connections are terminated than for keeping a connection alive TCP keepalives are disabled by default 4 13 4 Internet protocol This option allows the user to select between the old and new Internet protocols and addressing schemes IPv4 and IPv6 The default setting is Auto which means PuTTY will do something sensible and try to guess which protocol you wanted If you specify a literal Internet address it will use whichever protocol that address implies If you provide a hostname it will see what kinds of address exist for that hostname it will use IPv6 if there is an IPv6 address available and fall back to IPv4 if not If you need to force PuTTY to use a particular protocol you can explicitly set this to IPv4 or IPv6 4 14 The Data panel The Data panel allows you to configure various pieces of data which can be sent to the server to affect your connection at the far end http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 42 of 131 Each option on this panel applies to more than one protocol Options which apply to only one protocol appear on that protocol s configuration panels 4 14 1 Auto
211. otocols allow the client to specify terminal speeds to the server This parameter does _not_ affect the actual speed of the connection which is always as fast as possible it is just a hint that is sometimes used by server software to modify its behaviour For instance if a slow speed is indicated the server may switch to a less bandwidth hungry display mode he value is usually meaningless in a network environment but PuTTY lets you configure it in case you find the server is reacting badly to the default value The format is a pair of numbers separated by a comma for instance 38400 38400 The first number represents the output speed _from_ the server in bits per second and the second is the input speed _to_ the server Only the first is used in the Rlogin protocol This option has no effect on Raw connections 4 14 4 Setting environment variables on the server The Telnet protocol provides a means for the client to pass environment variables to the server Many Telnet servers have stopped supporting this feature due to security flaws but PuTTY still supports it for the benefit of any servers which have found other ways around the security problems than just disabling the whole mechanism http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 43 of 131 Version 2 of the SSH protocol also provides a similar mechanism which is easier to implement without security flaws
212. ou may also need to ensure that your home directory your ssh directory and any other files involved such as authorized_keys authorized_keys2 or authorization are not group writable or world writable You can typically do this by using a command such as chmod go w HOME SHOME ssh SHOME ssh authorized_keys Your server should now be configured to accept authentication using your private key Now you need to configure PuTTY to _attempt_ authentication using your private key You can do this in any of three ways Select the private key in PuTTY s configuration See section 4 20 7 for details http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 86 of 131 Specify the key file on the command line with the i option See section 3 8 3 18 for details Load the private key into Pageant see chapter 9 In this case PuTTY will automatically try to use it for authentication if it can Chapter 9 Using Pageant for authentication 9L Pageant is an SSH authentication agent It holds your private keys in memory already decoded so that you can use them often without needing to type a passphrase Getting started with Pageant Before you run Pageant you need to have a private key in PPK format See chapter 8 to find out how to generate and use one When you run Pageant it will put an icon of a computer wearing a hat into the System tray It will then sit and do nothing u
213. ou select Serial from the Connection type radio buttons the Host Name and Port boxes are replaced by Serial line and Speed see section 4 25 for more details of these 4 1 2 Loading and storing saved sessions The next part of the Session configuration panel allows you to save your preferred PuTTY options so they will appear automatically the next time you start PuTTY It also allows you to create _saved sessions_ which contain a full set of configuration options plus a host name and protocol A saved session contains all the information PuTTY needs to start exactly the session you want To save your default settings first set up the settings the way you want them saved Then come back to the Session panel Select the Default Settings entry in the saved sessions list with a single click Then press the Save button Note that PuTTY does not allow you to save a host name into the Default Settings entry This ensures that when PuTTY is started up the host name box is always empty so a user can always just type in a host name and connect If there is a specific host you want to store the details of how to connect to you should create a saved session which will be http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 sly sepa Each conf Sett Save HKI If y desc Glo Fina Wind disa like has opti Clo clos leav defa term abor the Pag
214. ould arrange that each key is _restricted_ so that it can only be used for that specific purpose The documentation for your SSH server should explain how to do this it will probably vary between servers Choosing a good passphrase is difficult Just as you shouldn t use a dictionary word as a password because it s easy for an attacker to run through a whole dictionary you should not use a song lyric quotation or other well known sentence as a passphrase DiceWare www diceware com recommends using at least five words ach generated randomly by rolling five dice which gives over 2 64 possible passphrases and is probably not a bad scheme If you want your passphrase to make grammatical sense this cuts down the possibilities a lot and you should use a longer one as a result _Do not forget your passphrase_ There is no way to recover it 8 2 8 Saving your private key to a disk file Once you have generated a key set a comment field and set a passphrase you are ready to save your private key to disk Press the Save private key button PuTTYgen will put up a dialog box asking you where to save the file Select a directory type ina file name and press Save This file is in PuTTY s native format PPK it is the one you will need to tell PuTTY to use for authentication see section 4 20 7 or tell Pageant to load see section 9 2 2 8 2 9 Saving your public key to a disk file RFC 4716 spec
215. our program This is what CVS for Windows does for example Details of PuTTY s operation What terminal type does PuTTY use For most purposes PuTTY can be considered to be an xterm terminal PuTTY also supports some terminal control sequences not supported by the real xterm notably the Linux console sequences that reconfigure the colour palette and the title bar control sequences used by DECterm which are different from the xterm ones PuTTY supports both By default PuTTY announces its terminal type to the server as xterm If you have a problem with this you can reconfigure it to say something else vt220 might help if you have trouble Where does PuTTY store its data On Windows PuTTY stores most of its data saved sessions SSH host keys in the Registry The precise location is HKEY_CURRENT_USER Software SimonTatham PuTTY and within that area saved sessions are stored under Sessions http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 101 of 131 hile host keys are stored under SshHostKeys PuTTY also requires a random number seed file to improve the unpredictability of randomly chosen data needed as part of the SSH cryptography This is stored by default in a file called PUTTY RND i t n your Windows home directory SHOMEDRIVES SHOMEPATHS or in he actual Windows directory such as C WINDOWS if the home directory doesn
216. ourth protocol _Raw_ is not used for interactive login sessions you would usually use this for debugging other Internet services s section 3 6 The fifth option _Serial_ is used for connecting to a local serial line and works somewhat differently see section 3 7 for more information on this When you change the selected protocol the number in the Port box will change This is normal it happens because the various login services are usually provided on different network ports by the server machine Most servers will use the standard port numbers so you will not need to change the port setting If your server provides login services on a non standard port your system administrator should have told you which one For example many MUDs run Telnet service on a port other than 23 Once you have filled in the Host Name Protocol and possibly Port settings you are ready to connect Press the Open button at the bottom of the dialog box and PuTTY will begin trying to connect you to the server 2 2 Verifying the host key SSH only If you are not using the SSH protocol you can skip this section If you are using SSH to connect to a server for the first time you will probably see a message looking something like this The server s host key is not cached in the registry You have no guarantee that the server is the computer you think it is The server s rsa2 key fingerprint is ssh rsa 1024
217. play location box if this is left blank PuTTY will try to find a sensible default in the environment or use the primary local display 0 if that fails See section 3 4 for more information about X11 forwarding 4 22 1 Remote X11 authentication If you are using X11 forwarding the virtual X server created on the SSH server machine will be protected by authorisation data This data is invented and checked by PuTTY The usual authorisation method used for this is called MIT MAGIC COOKIE 1 This is a simple password style protocol the X client sends some cookie data to the server and the server checks that it matches the real cookie The cookie data is sent over an unencrypted X11 connection so if you allow a client on a third machine to access the virtual X server then the cookie will be sent in the clear PuTTY offers the alternative protocol XDM AUTHORIZATION 1 This is a cryptographically authenticated protocol the data sent by the X client is different every time and it depends on the IP address and port of the client s end of the connection and is also stamped with the current time So an eavesdropper who captures an XDM AUTHORIZATION 1 string cannot immediately re use it for their own X connection PuTTY s support for XDM AUTHORIZATION 1 is a somewhat experimental feature and may encounter several problems Some X clients probably do not even support XDM AUTHORIZATION 1
218. r a backslash before any of the above characters or itself removes that character s special meaning A leading period on a filename is not treated specially unlike in some Unix contexts get will fetch all files whether or not they start with a leading period 6 2 3 The open command start a session If you started PSFTP by double clicking in the GUI or just by typing psftp at the command line you will need to open a connection to an SFTP server before you can issue any other commands except help and quit To create a connection type open host name or if you need to specify a user name as well you can type open user host name Once you have issued this command you will not be able to issue it again _even_ if the command fails for example if you mistype the host name or the connection times out So if the connection is not opened successfully PSFTP will terminate immediately 6 2 4 The quit command end your session When you have finished your session type the command quit to close the connection terminate PSFTP and return to the command line or just close the PSFTP console window if you started it from the GUI You can also use the bye and exit commands which have exactly http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 70 of 131 the same effect 6 2 5 The close command close your connection If you just want to
219. r and s http the earth li sgtatham putty 0 60 puttydoc txt this _shouldn t_ happen but it is whether they 7 11 2008 Page 91 of 131 expect the host key to have changed If so verify the new host key in the same way as you would if it was new See section 2 2 for more information on host keys 10 3 Out of space for port forwardings PuTTY has a fixed size buffer which it uses to store the details of all port forwardings you have set up in an SSH session If you specify too many port forwardings on the PuTTY or Plink command line and this buffer becomes full you will see this error message We need to fix this fixed size buffers are almost always a mistake but we haven t got round to it If you actually have trouble with this let us know and we ll move it up our priority list 10 4 The first cipher supported by the server is below the configured warning threshold This occurs when the SSH server does not offer any ciphers which you have configured PuTTY to consider strong enough By default PuTTY puts up this warning only for single DES and Arcfour encryption See section 4 18 5 for more information on this message 10 5 Server sent disconnect message type 2 protocol error Too many authentication failures for root This message is produced by an OpenSSH or Sun SSH server if it receives more failed authentication attempts than it is willing to tolerate This ca
220. r does not gain your private key or password they only gain ne signature And signatures cannot be re used so they have gained othing There is a problem with this if your private key is stored unprotected on your own computer then anybody who gains access to _that_ will be able to generate signatures as if they were you So they will be able to log in to your server under your account For this reason your private key is usually _encrypted_ when it is stored on your local machine using a passphrase of your choice In order to generate a signature PuTTY must decrypt the key so you have to type your passphrase This can make public key authentication less convenient than password authentication every time you log in to the server instead of typing a short password you have to type a longer passphrase One solution to this is to use an _authentication agent_ a separate program which holds decrypted private keys and generates signatures on request PuTTY s authentication agent is called Pageant When you begin a Windows session you start Pageant and load your private key into it typing your passphrase once For the rest of your session you can start PuTTY any number of times and Pageant will automatically generate signatures without you having to do anything When you close your Windows session Pageant shuts down without ever having stored your decrypted private key on disk Many people feel this is a good compromis
221. ring multiple times at the keyboard If you set the answerback string to be empty this problem should go away but doing so might cause other problems A ga Note that this is _not_ the feature of PuTTY which the server will typically use to determine your terminal type That feature is the Terminal type string in the Connection panel see section 4 14 2 for details You can include control characters in the answerback string using C notation Use to get a literal 4 3 7 Local echo With local echo disabled characters you type into the PuTTY window are not echoed in the window _by PuTTY_ They are simply sent to the server The _server_ might choose to echo them back to you this can t be controlled from the PuTTY control panel Some types of session need local echo and many do not In its default mode PuTTY will automatically attempt to deduce whether or not local echo is appropriate for the session you are working in If you find it has made the wrong decision you can use this configuration option to override its choice you can force local echo to be turned on or force it to be turned off instead of relying on the automatic detection 4 3 8 Local line editing Normally every character you type into the PuTTY window is sent immediately to the server the moment you type it If you enable local line editing this changes PuTTY will let you edit a whole
222. root on the Unix box Of course we don t believe any of those things is very likely We know our sysadmin personally and trust him both to be competent and to be non malicious and we take all reasonable precautions to guard the build machine But when you see a signature you should always be certain of precisely what it guarantees and precisely what it does not E N N he Releases keys The Release keys have passphrases and we can be more careful about how we use them The Release keys are kept safe on the developers own local machines and only used to sign releases that have been built by hand A signature from a Release key protects you from almost any plausible attack Some of the developers machines have cable modem connections and might in theory be crackable but of course the private keys are still encrypted so the crack would have to go unnoticed for long enough to steal a passphrase E 2 3 The Master Keys http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 131 of 131 The Master Keys sign almost nothing Their purpose is to bind the other keys together and certify that they are all owned by the same people and part of the same integrated setup The only signatures produced by the Master Keys _ever_ should be the signatures on the other keys We intend to arrange for the Master Keys to sign each other to certify that the DSA keys and RSA keys are part o
223. rver a bit like hanging up a telephone unexpectedly in the middle of a conversation We recommend you do not do this unless the server has stopped responding to you and you cannot close the window any other way Chapter 3 Using PuTTY This chapter provides a general introduction to some more advanced http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 5 of 131 features of PuTTY For extreme detail and reference purposes chapter 4 is likely to contain more information 3 1 During your session A lot of PuTTY s complexity and features are in the configuration panel Once you have worked your way through that and started a session things should be reasonably simple after that Nevertheless there are a few more useful features available 3 1 1 Copying and pasting text Often in a PuTTY session you will find text on your terminal screen which you want to type in again Like most other terminal emulators PuTTY allows you to copy and paste the text rather than having to type it again Also copy and paste uses the Windows clipboard so that you can paste for example URLS into a web browser or paste from a word processor or spreadsheet into your terminal session PuTTY s copy and paste works entirely with the mouse In order to copy text to the clipboard you just click the left mouse button in the terminal window and drag to select text When you let go of the button the text is _automatical
224. sion is still open it will be up to date and if the client system crashes there s a greater chance that the data will be preserved However this can incur a performance penalty If PuTTY is running slowly with logging enabled you could try unchecking this option Be warned that the log file may not always be up to date as a result although it will of course be flushed when it is closed for instance at the end of a session 4 2 4 Options specific to SSH packet logging These options only apply if SSH packet data is being logged The following options allow particularly sensitive portions of unencrypted packets to be automatically left out of the log file They are only intended to deter casual nosiness an attacker could glean a lot of useful information from even these obfuscated logs e g length of password 4 2 4 1 Omit known password fields When checked decrypted password fields are removed from the log of transmitted packets This includes any user responses to challenge response authentication methods such as keyboard interactive This does not include X11 authentication data if using X11 forwarding Note that this will only omit data that PuTTY _knows_ to be a password However if you start another login session within your PuTTY session for instance any password used will appear in the clear in the packet log The next option may be of use to protect against this
225. software Group exchange with this method instead of using a fixed group PuTTY requests that the server suggest a group to use for key exchange the server can avoid groups known to be weak and possibly invent new ones over time without any changes required to PuTTY s configuration We recommend use of this method if possible http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 4 19 2 Page 50 of 131 If the first algorithm PuTTY finds is below the warn below here line you will see a warning box when you make the connection Similar to that for cipher selection see section 4 18 5 Repeat key exchange If the session key negotiated at connection startup is used too much or for too long it may become feasible to mount attacks against the SSH connection Therefore the SSH 2 protocol specifies that a new key exchange should take place every so often this can be initiated by either the client or the server While this renegotiation is taking place no data can pass through the SSH connection so it may appear to freeze The occurrence of repeat key exchange is noted in the Event Log see section 3 1 3 1 Usually the same algorithm is used as at the start of the connection with a similar overhead These options control how often PuTTY will initiate a repeat key exchange rekey You can also force a key exchange at any time from the Special Commands menu s
226. source c c source However in the second case using a wildcard for multiple remote files you may see a warning saying something like warning remote host tried to write to a file called terminal c when we requested a file called c If this is a wildcard consider upgrading to http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 63 of 131 SSH 2 or using the unsafe option Renaming of this file has been disallowed This is due to a fundamental insecurity in the old style SCP protocol the client sends the wildcard string c to the server and the server sends back a sequence of file names that match the wildcard pattern However there is nothing to stop the server sending back a _different_ pattern and writing over one of your other files if you request c the server might send back the file name AUTOEXEC BAT and install a virus for you Since the wildcard matching rules are decided by the server the client cannot reliably verify that the filenames sent back match the pattern PSCP will attempt to use the newer SFTP protocol part of SSH 2 where possible which does not suffer from this security flaw If you are talking to an SSH 2 server which supports SFTP you will never see this warning You can force use of the SFTP protocol if available with sftp see section 5 2 2 6 If you really need to use a server side wildcard with
227. sswords so these servers will crash when they s the RSA attempt If this bug is detected PuTTY will go straight to password authentication If this bug is enabled when talking to a correct server the session will succeed but of course RSA authentication will be impossible This is an SSH 1l specific bug 4 24 4 Miscomputes SSH 2 HMAC keys Versions 2 3 0 and below of the SSH server software from ssh com compute the keys for their HMAC message authentication codes incorrectly A typical symptom of this problem is that PuTTY dies unexpectedly at the beginning of the session saying Incorrect MAC received on packet If this bug is detected PuTTY will compute its HMAC keys in the same way as the buggy server so that communication will still be possible If this bug is enabled when talking to a correct server communication will fail This is an SSH 2 specific bug 4 24 5 Miscomputes SSH 2 encryption keys Versions below 2 0 11 of the SSH server software from ssh com compute the keys for the session encryption incorrectly This problem can cause various error messages such as Incoming packet was garbled on decryption or possibly even Out of memory If this bug is detected PuTTY will compute its encryption keys in the same way as the buggy server so that communication will still be possible If this bug is enabled when talking to a correct server communication will fail This is an SSH
228. t a he server does not provide the service which PuTTY is trying to Check that you are connecting with the correct protocol SSH Telnet or Rlogin and check that the port number is correct If that fails consult the administrator of your server 10 17 Network error Connection timed out http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 95 of 131 This error means that the network connection PuTTY tried to make to your server received no response at all from the server Usually this happens because the server machine is completely isolated from the network or because it is turned off Check that you have correctly entered the host name or IP address of your server machine If that fails consult the administrator of your server Unix also generates this error when it tries to send data down a connection and contact with the server has been completely lost during a connection There is a delay of minutes before Unix gives up on receiving a reply from the server This can occur if you type things into PuTTY while the network is down but it can also occur if PuTTY decides of its own accord to send data due to a repeat key exchange in SSH 2 see section 4 19 2 or due to keepalives section 4 13 1 Appendix A PuTTY FAQ This FAQ is published on the PuTTY web site and also provided as an appendix in the manual Introduction What is PuTTY PuTTY is a client program for the S
229. t a lot so a they would fill up the scrollback with a large amount of unhelpfully disordered text and b they contain their _own_ method for the user to scroll back to the bit they were interested in We have generally found this policy to do the Right Thing in almost all situations Unfortunately screen is one exception it uses the alternat screen but it s still usually helpful to have PuTTY s scrollback continue working The simplest solution is to go to the Features control panel and tick Disable switching to alternate terminal screen See section 4 6 4 for more details Alternatively you can tell screen itself not to use the alternate screen th screen FAQ suggests adding the line termcapinfo xterm ti te to your screenrc file The reason why this only started to be a problem in 0 54 is because screen typically uses an unusual control sequence to switch to the alternate screen and previous versions of PuTTY did not support this sequence Since I upgraded Windows XP to Service Pack 2 I can t use addresses like 127 0 0 2 Some people who ask PuTTY to listen on localhost addresses other than 127 0 0 1 to forward services such as SMB and Windows Terminal Services have found that doing so no longer works since they upgraded to WinXP SP2 This is apparently an issue with SP2 that is acknowledged by Microsoft in MS Knowledge Base article 884020 The article links to
230. t a member of the PuTTY core development team The putty bugs mailing list is not a general newsgroup like discussion forum it s a contact address for the core developers and an _internal_ mailing list for us to discuss things among ourselves If we opened it up for everybody to subscribe to it would turn into something more like a newsgroup and we would be completely overwhelmed by the volume of traffic It s hard enough to keep up with the list as it is A 9 6 If putty bugs isn t a general subscription mailing list what is There isn t one that we know of If someone else wants to set up a mailing list or other forum for PuTTY users to help each other with common problems that would be fine with us though the PuTTY team would almost certainly not have the time to read it It s probably better to use one of the established newsgroups for this purpose see section B 1 2 A 9 7 How can I donate to PuTTY development Please _please_ don t feel you have to PuTTY is completely free software and not shareware We think it s very important that _everybody_ who wants to use PuTTY should be able to whether they have any money or not so the last thing we would want is for a PuTTY user to feel guilty because they haven t paid us any money If you want to keep your money please do keep it We wouldn t dream of asking for any Having said all that if you still really _want_ to give us
231. t exist for example if you re using Win95 If you want to change the location of the random number seed file you can put your chosen pathname in the Registry at HKEY_CURRENT_USER Software SimonTatham PuTTY RandSeedFile You can ask PuTTY to delete all this data see question A 8 2 On Unix PuTTY stores all of this data in a directory putty A 6 HOWTO questions A 6 1 What login name password should I use This is not a question you should be asking _us_ PuTTY is a communications tool for making connections to other computers We maintain the tool we _don t_ administer any computers that you re likely to be able to use in the same way that the people who make web browsers aren t responsible for most of the content you can view in them We cannot help with questions of this sort If you know the name of the computer you want to connect to but don t know what login name or password to use you should talk to whoever administers that computer If you don t know who that is S the next question for some possible ways to find out A 6 2 What commands can I type into my PuTTY terminal window Again this is not a question you should be asking _us_ You need to read the manuals or ask the administrator of _the computer you have connected to_ PuTTY does not process the commands you type into it It s only a communications tool It makes a connection to another computer it passes the commands yo
232. t repeat key exchanges see section 4 19 2 Break Only available in SSH 2 and only during a session Optional extension may not be supported by server PuTTY requests the server s default break length Signals SIGINT SIGTERM etc Only available in SSH 2 and only during a session Sends various POSIX signals Not honoured by all servers With a serial connection the only available special command is Break 3 1 3 3 Starting new sessions PuTTY s system menu provides some shortcut ways to start new sessions http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 8 of 131 Selecting New Session will start a completely new instance of PuTTY and bring up the configuration box as normal Selecting Duplicate Session will start a session in a new window with precisely the same options as your current one connecting to the same host using the same protocol with all the same terminal settings and everything In an inactive window selecting Restart Session will do the same as Duplicate Session but in the current window The Saved Sessions submenu gives you quick access to any sets of stored session details you have previously saved See section 4 1 2 for details of how to create saved sessions 3 1 3 4 Changing your session settings If you select Change Settings from the system menu PuTTY will display a cut down version of its initial
233. t the main point of Plink In order to connect with a different protocol you can give the command line options ssh telnet rlogin or raw To make an SSH connection for example Z sysosd gt plink ssh login example com login as If you have already set up a PuTTY saved session then instead of supplying a host name you can give the saved session name This allows you to use public key authentication specify a user name and use most of the other features of PuTTY Z sysosd gt plink my ssh session http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 77 of 131 Sent username fred Authenticating with public key fred winbox Last login Thu Dec 6 19 25 33 2001 from 0 0 fred flunky You can also use the load command line option to load a saved session see section 3 8 3 1 If you use load the saved session exists and it specifies a hostname you cannot also specify a host or user host argument it will be treated as part of the remote command 7 2 2 Using Plink for automated connections More typically Plink is used with the SSH protocol to enable you to talk directly to a program running on the server To do this you have to ensure Plink is _using_ the SSH protocol You can do this in several ways Use the ssh option as described in section 7 2 1 Set up a PuTTY saved session that describes the server you are connecting to and
234. t_ the the server from doing this can therefore log in to other machines as you to a limited extent when th sysadmin or hackers on Therefore if should _never_ us also shouldn t store private keys on that machine into it or log into other machines from it in any Pageant is hardly unique in this respect you don t Common error messages 10 10 trust the sysadmin of a server machine agent forwarding to that machine Page 90 of 131 the server machine can always pretend to So if you forward your agent to a server then the sysadmin of that machine can access the forwarded and you Of course you type passphrases way at all This chapter lists a number of common error messages which PuTTY and its associated tools can produce more detail We do not attempt to list _all_ error messages her and explains what they mean in there are many which should never occur and some which should be If you get an error message which is not listed in self explanatory this chapter and which you don t understand B and we will add documentation for it The server s This error message occurs when PuTTY connects to a Every server identifies its it will b report it to us as a bug lf by means of a host key able to see appendix host key is not cached in the registry new SSH server once PuTTY detect if a knows the host key for a server
235. taining B In the other mode Rectangular block dragging the mouse between two points defines a rectangle and everything within that rectangle is copied Normally you have to hold down Alt while dragging the mouse to select a rectangular block Using the Default selection mode control you can set rectangular selection as the default and then you have to hold down Alt to get the _normal_ behaviour 4 11 5 Configuring word by word selection PuTTY will select a word at a time in the terminal window if you double click to begin the drag This panel allows you to control precisely what is considered to be a word Each character is given a _class_ which is a small number typically 0 1 or 2 PuTTY considers a single word to be any number of adjacent characters in the same class So by modifying the assignment of characters to classes you can modify the word by word selection behaviour In the default configuration the character classes are Class 0 contains white space and control characters Class 1 contains most punctuation Class 2 contains letters numbers and a few pieces of punctuation the double quote minus sign period forward slash and underscore So for example if you assign the symbol into character class 2 you will be able to select an e mail address with just a double click In order to adjust these assignments you start by selecting a group of char
236. tead but this is not the default because most Windows users don t have a middle button at all You can also paste by pressing Shift Ins A 6 7 How do I use all PuTTY s features public keys proxying cipher selection etc in PSCP PSFTP and Plink ost major features e g public keys port forwarding are available through command line options See the documentation Not all features are accessible from the command line yet although we d like to fix this In the meantime you can use most of PuTTY s features if you create a PuTTY saved session and then use the nam of the saved session on the command line in place of a hostname This works for PSCP PSFTP and Plink but don t expect port forwarding in the file transfer applications A 6 8 How do I use PSCP EXE When I double click it gives me a command prompt window which then closes instantly PSCP is a command line application not a GUI application If you run it without arguments it will simply print a help message and terminate http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 103 of 131 To use PSCP properly run it from a Command Prompt window See chapter 5 in the documentation for more details A 6 9 How do I use PSCP to copy a file whose name has spaces in If PSCP is using the traditional SCP protocol this is confusing If you re specifying a file at the local end you just use one set of quotes as
237. terested in trading links for other links since we have no advertising on our web site our Google ranking is not even directly worth anything to us If we don t want to link to you for free then we probably won t want to link to you at all If you have software based on PuTTY or specifically designed to interoperate with PuTTY or in some other way of genuine interest to PuTTY users then we will probably be happy to add a link to you on our Links page And if you re running a mirror of the PuTTY web site we re _definitely_ interested A 9 4 Why don t you move PuTTY to SourceForge Partly because we don t want to move the web site location see question A 9 1 lso security reasons PuTTY is a security product and as such it s particularly important to guard the code and the web site against nauthorised modifications which might introduce subtle security laws Therefore we prefer that the Subversion repository web ite and FTP site remain where they are under the direct control f system administrators we know and trust personally rather than being run by a large organisation full of people we ve never met and which is known to have had breakins in the past On ms FB No offence to SourceForge I think they do a wonderful job But they re not ideal for everyone and in particular they re not ideal for us A 9 5 Why can t I subscribe to the putty bugs mailing list Because you re no
238. tion 2 2 then the connection will simply be abandoned instead of asking you what to do next This may help Plink s behaviour when it is used in automated scripts using batch if something goes wrong at connection time the batch job will fail rather than hang 7 2 3 2 s remote command is SSH subsystem If you specify the s option Plink passes the specified command as the name of an SSH subsystem rather than an ordinary command line This option is only meaningful with the SSH 2 protocol 7 3 Using Plink in batch files and scripts Once you have set up Plink to be able to log in to a remote server without any interactive prompting see section 7 2 2 you can use it for lots of scripting and batch purposes For example to start a backup on a remote machine you might use a command like plink root myserver etc backups do backup sh Or perhaps you want to fetch all system log lines relating to a particular web area plink mysession grep fred var log httpd access log gt fredlog Any non interactive command you could usefully run on the server command line you can run in a batch file using Plink in this way http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 79 of 131 7 4 Using Plink with CVS To use Plink with CVS you need to set the environment variable CVS_RSH to point to Plink set CVS_RSH path to plink exe You also need to arrange to be able to connect
239. to a remote host without any interactive prompts as described in section 7 2 2 You should then be able to run CVS as follows cvs d ext user sessionname path to repository co module If you specified a username in your saved session you don t even need to specify the user part of this and you can just say cvs d ext sessionname path to repository co module 7 5 Using Plink with WinCVS Plink can also be used with WinCVS Firstly arrange for Plink to be able to connect to a remote host non interactively as described in section 7 2 2 Then in WinCVS bring up the Preferences dialogue box from the _Admin_ menu and switch to the Ports tab Tick the box there labelled Check for an alternate rsh name and in the text entry field to the right enter the full path to plink exe Select OK on the Preferences dialogue box Next select Command Line from the WinCVS Admin menu and type a CVS command as in section 7 4 for example cvs d ext user hostname path to repository co module or if you re using a saved session cvs d ext user sessionname path to repository co module Select the folder you want to check out to with the Change Folder button and click OK to check out your module Once you ve got modules checked out WinCVS will happily invoke plink from the GUI for CVS operations Chapter 8 Using public keys for SSH authentication 8 1 Public ke
240. to function key presses by sending a sequence of control characters to the server If a function key isn t doing what you expect it s likely that the character sequence your application is expecting to receive is not the same as the one PuTTY is sending Therefore what we really need to know is _what_ sequence the application is expecting The simplest way to investigate this is to find some other terminal environment in which that function key _does_ work and then investigate what sequence the function key is sending in that situation One reasonably easy way to do this on a Unix system is to type the command cat and then press the function key This is likely to produce output of the form 11 You can also do this in PuTTY to find out what sequence the function key is producing in that Then you can mail the PuTTY maintainers and tell us I wanted the Fl key to send 11 but instead it s sending OP can this be done or something similar You should still read the Feedback page on the PuTTY website also provided as appendix B in the manual and follow the guidelines contained in that http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 108 of 131 A 7 16 Since my SSH server was upgraded to OpenSSH 3 1p1 3 4p1 I can no A 7 17 A 7 18 longer connect with PuTTY There is a known problem when OpenSSH has been built against an incorrect version of OpenSSL the q
241. to the server Some accessibility programs for Windows may need this option enabling to be able to control PuTTY s window successfully For instance Dragon NaturallySpeaking requires it both to open the system menu via voice and to close minimise maximise and restore the window 4 9 5 System menu appears on Alt alone If this option is enabled then pressing and releasing ALT will bring up the PuTTY window s menu like clicking on the top left corner If it is disabled then pressing and releasing ALT will have no effect 4 9 6 Ensure window is always on top If this option is enabled the PuTTY window will stay on top of all other windows 4 9 7 Full screen on Alt Enter If this option is enabled then pressing Alt Enter will cause the PuTTY window to become full screen Pressing Alt Enter again will http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 4 10 1 4 10 2 http the earth li sgtatham putty 0 60 puttydoc txt Page 35 of 131 restore the previous window size The full screen feature is also available from the System menu even when it is configured not to be available on the Alt Enter key S section 3s Dasa Nhs he Translation panel he Translation configuration panel allows you to control the translation between the character set understood by the server and the character set understood
242. total number of 1 bits is even Mark an extra parity bit is sent alongside each byte and always set to l Space an extra parity bit is sent alongside each byte and always set to 0 4 25 6 Selecting the serial flow control scheme The Flow control box allows you to choose what type of flow control checking is used on the serial line The settings are None no flow control is done Data may be lost if either side attempts to send faster than the serial line permits XON XOFF flow control is done by sending XON and XOFF characters within the data stream RTS CTS flow control is done using the RTS and CTS wires on the serial line DSR DTR flow control is done using the DSR and DTR wires on the serial line 4 26 Storing configuration in a file PuTTY does not currently support storing its configuration ina file instead of the Registry However you can work around this with a couple of batch files You will need a file called say PUTTY BAT which imports the contents of a file into the Registry then runs PuTTY exports the contents of the Registry back into the file and deletes the Registry entries This can all be done using the Regedit command line options so it s all automatic Here is what you need in PUTTY BAT ECHO OFF regedit s putty reg regedit s puttyrnd reg http the earth li sgtatham putty 0 60 puttydoc txt 7 1
243. tually stored In addition if you have a private key on one of the SSH servers you can send it all the way back to Pageant using the local ssh add command unixbox S ssh add ssh id_rsa Need passphrase for home fred ssh id_rsa Enter passphrase for home fred ssh id_rsa Identity added home fred ssh id_rsa home simon ssh id_rsa unixbox and then it s available to every machine that has agent forwarding available not just the ones downstream of the place you added it 9 5 Security considerations Using Pageant for public key authentication gives you the convenience of being able to open multiple SSH sessions without having to type a passphrase every time but also gives you the o security benefit of never storing a decrypted private key on disk Many people feel his is a good compromise between security and convenience It _is_ a compromise however Holding your decrypted private keys in Pageant is better than storing them in easy to find disk files but still less secure than not storing them anywhere at all This is for two reasons Windows unfortunately provides no way to protect pieces of memory from being written to the system swap file So if Pageant is holding your private keys for a long period of time it s possible that decrypted private key data may be written to the system swap file and an attacker who gained access to your hard disk later on might be able
244. u type to that other computer and it passes the other computer s responses back to you Therefore the precis range of commands you can use will not depend on PuTTY but on what kind of computer you have connected to and what software is running on it The PuTTY team cannot help you with that Think of PuTTY as being a bit like a telephone If you phone somebody up and you don t know what language to speak to make them understand you it isn t _the telephone company_ s job to find that out for you We just provide the means for you to get in touch making yourself understood is somebody else s problem If you are unsure of where to start looking for the administrator of your server a good place to start might be to remember how you found out the host name in the PuTTY configuration If you were given that host name by e mail for example you could try asking the person who sent you that e mail If your company s IT department provided you with ready made PuTTY saved sessions then that IT department can probably also tell you something about what commands you can type during those sessions But the PuTTY maintainer team does not administer any server you are likely to be connecting to http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 102 of 131 and cannot help you with questions of this type A 6 3 How can I make PuTTY start up maximised Create a Windows shortcut to start PuTTY from a
245. uTTY files distributed from our web site so that users can be confident that the files have not been tampered with Here we identify our public keys and explain our signature policy so you can have an accurate idea of what each signature guarantees This description is provided as both a web page on the PuTTY site and an appendix in the PuTTY manual As of release 0 58 all of the PuTTY executables contain fingerprint material usually accessed via the pgpfp command line option such that if you have an executable you trust you can use it to establish a trust path for instance to a newer version downloaded from the Internet Note that none of the keys signatures tc mentioned here hav anything to do with keys used with SSH they are purely for verifying the origin of files distributed by the PuTTY team Public keys We supply two complete sets of keys We supply a set of RSA keys compatible with both GnuPG and PGP2 and also a set of DSA keys compatible with GnuPG In each format we have thr keys A Development Snapshots key used to sign the nightly builds A Releases key used to sign actual releases A Master Key The Master Key is used to sign the other two keys and they sign it in return Therefore we have six public keys in total RSA Master Key Release key Snapshot key Master Key 1024 bit fingerprint 8F 15 97 DA 25 30 AB OD 88 D1 92 54 11 CF OC 4C http the eart
246. ugh you can still the keyboard as described in sec configure whether th normal modes If you are viewing part of the scrollback when th more text to PuTTY terminal contents revert when you press a key keypress a es The Display scrol ts you configure how many lines of lbar options allow you to hide view the scrollback using tion 3 1 2 You can separately scrollbar is shown in full screen mode and in server sends the screen will revert to showing the current You can disable this behaviour by turning off Reset scrollback on display activity by turning on Reset scrollback on You can also make the screen Push erased text into scrollback contents of the terminal screen When this option is enabled th will be pushed into the scrollback when a server sid clears the screen record of what was on your scree If the application switches to t 4 6 4 for more about this then will be visible in the scrollbac back again This option is enabled by default http the earth li sgtatham putty 0 60 puttydoc txt application so that your scrollback will contain a better n in the past he alternate screen s section the contents of the primary screen k until the application switches 7 11 2008 Page 33 of 131 4 8 The Appearance panel The Appearance configuration panel allows you to control aspects of the appearance of PuTTY s window 4 8
247. uick workaround is to configure PuTTY to use SSH protocol 2 and the Blowfish cipher For more details and OpenSSH patches see bug 138 in the OpenSSH BTS This is not a PuTTY specific problem if you try to connect with another client you ll likely have similar problems Although PuTTY s default cipher differs from many other clients _OpenSSH 3 1pl1l _ configurations known to be broken and symptoms SSH 2 with AES cipher PuTTY says Assertion failed Expression len amp 15 0 in sshaes c or Out of memory or crashes SSH 2 with 3DES PuTTY says Incorrect MAC received on packet SSH 1 with Blowfish PuTTY says Incorrect CRC received on packet SSH 1 with 3DES _OpenSSH 3 4pl1l _ as of 3 4pl1 only the problem with SSH 1 and Blowfish remains Rebuild your server apply the patch linked to from bug 138 above or use another cipher e g 3DES instead _Other versions _ we occasionally get reports of the same symptom and workarounds with older versions of OpenSSH although it s not clear the underlying cause is the same Why do I see Couldn t load private key from Why can PuTTYgen load my key but not PuTTY It s likely that you ve generated an SSH protocol 2 key with PuTTYgen but you re trying to use it in an SSH 1 connection SSH 1 and SSH 2 keys have different formats and at least in 0 52 PuTTY s reporting of a key in the wrong format isn
248. ul if you confer with us first there may be design issues you haven t thought of or we may be about to make big changes to the code which your patch would clash with or something If you check with the maintainers first there is a better chance of your code actually being usable Also read the design principles listed in appendix D if you do not conform to them we will probably not be able to accept your patch B 4 Requesting features that have already been requested If a feature is already listed on the Wishlist then it usually means we would like to add it to PuTTY at some point However this may not be in the near future If there s a feature on the Wishlist which you would like to see in the _near_ future there are several things you can do to try to increase its priority level Mail us and vote for it Be sure to mention that you ve seen it on the Wishlist or we might think you haven t even _read_ the Wishlist This probably won t have very _much_ effect if a huge number of people vote for something then it may make a difference but one or two extra votes for a particular feature are unlikely to change our priority list immediately Offering a new and compelling justification might help Also don t expect a reply Offer us money if we do the work sooner rather than later This sometimes works but not always The PuTTY team all have full time jobs and we re doing all of this work in our
249. use press Ctrl C to copy it to the clipboard and then paste the data into a PuTTY session which is already connected to the server See section 8 3 for general instructions on configuring public key authentication once you have generated a key 8 2 11 Reloading a private key PuTTYgen allows you to load an existing private key file into memory If you do this you can then change the passphrase and comment before saving it again you can also make extra copies of the public key To load an existing key press the Load button PuTTYgen will put up a dialog box where you can browse around the file system and find your key file Once you select the file PuTTYgen will ask you fora passphrase if necessary and will then display the key details in the same way as if it had just generated the key If you use the Load command to load a foreign key format it will work but you will see a message box warning you that the key you have loaded is not a PuTTY native key S section 8 2 12 for information about importing foreign key formats 8 2 12 Dealing with private keys in other formats Most SSH 1 clients use a standard format for storing private keys on disk PuTTY uses this format as well so if you have generated an SSH 1 private key using OpenSSH or ssh com s client you can use it with PuTTY and vice versa However SSH 2 private keys have no standard format OpenSSH and ssh com have d
250. which would tend to fail independently Failing that see if you can persuade an insurance company to insure you against security incidents and if the insurer demands it as a condition then get our code reviewed by a security engineer they re happy with Can you sign this form granting us permission to use distribute PuTTY If your form contains any clause along the lines of the undersigned represents and warrants we re not going to sign it This is particularly true if it asks us to warrant that PuTTY is secure see question A 9 9 for more discussion of this But it doesn t really matter what we re supposed to be warranting even if it s something we already believe is true such as that we don t infringe any third party copyright we will not sign a document accepting any legal or financial liability This is simply because the PuTTY development project has no income out of which to satisfy that liability or pay legal costs should it become necessary We cannot afford to be sued We are assuring you that _we have done our best _ if that isn t good enough for you tough The existing PuTTY licence document already gives you permission to use or distribute PuTTY in pretty much any way which does not involve pretending you wrote it or suing us if it goes wrong We think that really ought to be enough for anybody See also question A 9 12 for another reason why we don t want to do this sort of thing
251. x system to pretend it s talking to a real physical terminal device but allows t a he SSH server to catch all the data coming from that fake device nd send it back to the client Occasionally you might find you have a need to run a session _not_ in a pseudo terminal In PuTTY this is generally only useful for very specialist purposes although in Plink see chapter 7 it is the usual way of working http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 4 21 2 Sending terminal modes The SSH protocol allows the client to send terminal modes th If your server does not hav may find t remot expectatio of this None of t it s saf pseudo terminal n of the local sensibl hat changing them here hel to leav thes Page 53 of 131 for These usually control the server s terminal s behaviour defaults for these modes ps is requested or allocated You can add or modify a mode by selecting it fro list with the radio buttons and edit box several Remove choosing whether it s set automaticall Th By default hould do the rig S N If a mode is not on the list settings alone it will server under any circumstances If a mode is on the list precis If the so PuTTY proper will se Auto Plink on Unix will propagate appropriate modes from local terminal if any If a value is specified it w
252. xt te formatting information to the clipboard as well text you copy The effect of this is that if you paste into say a word processor the text will appear in the word processor in t he same font colour and style e g bold underline PuTTY was using to display it This option ca disabled n easily be inconvenient so by default it is 4 11 2 Changing the actions of the mouse buttons PuTTY s copy and paste mechanism is by default modelled on the Unix xterm application The X Window System uses a three button mouse and the convention is that the left button selects the right button extends an existing selection and the middle button pastes Windows often only has two mouse buttons so in PuTTY s default configuration Compromise the _right_ button pastes and the _middle_ button if you have one extends a selection If you have a three button mouse and you are already used to the xterm arrangement you can select it using the Action of mouse buttons control Alternatively with the Windows option selected the middle button extends and the right button brings up a context menu on which one of the options is Paste This context menu is always available by holding down Ctrl and right clicking regardless of the setting of this option 2 4 11 3 Shift overrides application s use of mouse PuTTY allows t over the mouse Applicatio
253. y authentication an introduction Public key authentication is an alternative means of identifying yourself to a login server instead of typing a password It is more secure and more flexible but more difficult to set up In conventional password authentication you prove you are who you claim to be by proving that you know the correct password The only way to prove you know the password is to tell the server what you think the password is This means that if the server has been hacked or _spoofed_ see section 2 2 an attacker can learn your password Public key authentication solves this problem You generate a _key pair_ consisting of a public key which everybody is allowed to http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 80 of 131 know and a private key which you keep secret and do not give to anybody The private key is able to generate _signatures_ A signature created using your private key cannot be forged by anybody who does not have that key but anybody who has your public key can verify that a particular signature is genuine So you generate a key pair on your own computer and you copy the public key to the server Then when the server asks you to prove who you are PuTTY can generate a signature using your private key The server can verify that signature since it has your public key and allow you to log in Now if the server is hacked or spoofed the a fe n ttacke
254. you modify this option in mid session using Change Settings it will take effect immediately 4 3 2 DEC Origin Mode initially on iw EC Origin Mode is a minor option which controls how PuTTY nterprets cursor position control sequences sent by the server ji The server can send a control sequence that restricts the scrolling region of the display For example in an editor the server might reserve a line at the top of the screen and a line at the bottom and might send a control sequence that causes scrolling operations to affect only the remaining lines With DEC Origin Mode on cursor coordinates are counted from the top of the scrolling region With it turned off cursor coordinates are counted from the top of the whole screen regardless of the scrolling region It is unlikely you would need to change this option but if you find a full screen application is displaying pieces of text in what looks like the wrong part of the screen you could try turning DEC Origin Mode on to see whether that helps DEC Origin Mode can be turned on and off by control sequences sent by the server This configuration option controls the _default_ state which will be restored when you reset the terminal see section 3 1 3 6 However if you modify this option in mid session using Change Settings it will take effect immediately 4 3 3 Implicit CR in every LF http the earth li sgtath
255. you specify and to copy them and their contents This allows you to use PSCP to transfer http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 65 of 131 whole directory structures between machines 5 2 2 5 batch avoid interactive prompts If you use the batch option PSCP will never give an interactive prompt while establishing the connection If the server s host key is invalid for exampl s section 2 2 then the connection will simply be abandoned instead of asking you what to do next This may help PSCP s behaviour when it is used in automated scripts using batch if something goes wrong at connection time the batch job will fail rather than hang 5 2 2 6 sftp scp force use of particular protocol As mentioned in section 5 2 1 there are two different file transfer protocols in use with SSH Despite its name PSCP like many other ostensible scp clients can use either of these protocols The older SCP protocol does not have a written specification and leaves a lot of detail to the server platform Wildcards are expanded on the server The simple design means that any wildcard specification supported by the server platform such as brace expansion can be used but also leads to interoperability issues such as with filename quoting for instance where filenames contain spaces and also the security issue described in section 5 2 1 The newer SFTP protocol which is usually
256. you ve only changed 10 lines we d prefer to receive a mail that s 30 lines long than one containing multiple http the earth li sgtatham putty 0 60 puttydoc txt 7 11 2008 Page 118 of 131 megabytes of data we already have B 1 2 Other places to ask for help There are two Usenet newsgroups that are particularly relevant to the PuTTY tools Pl If comp security ssh for questions specific to using the SSH protocol comp terminals for issues relating to terminal emulation for instance keyboard problems ase use the newsgroup most appropriate to your query and remember that these are general newsgroups not specifically about PuTTY you don t have direct access to Usenet you can access these newsgroups through Google Groups groups google com B 2 Reporting bugs If be If to you think you have found a bug in PuTTY your first steps should Check the Wishlist page on the PuTTY website and see if we already know about the problem If we do it is almost certainly not necessary to mail us about it unless you think you have extra information that might be helpful to us in fixing it Of course if we actually _need_ specific extra information about a particular bug the Wishlist page will say so Check the Change Log on the PuTTY website and s if we hav already fixed the bug in the development snapshots Check the FAQ on the PuTTY website also provided
257. you would normally do pscp local filename with spaces user host pscp user host myfile local filename with spaces But if the filename you re specifying is on the _remote_ side you have to use backslashes and two sets of quotes pscp user host remote filename with spaces local_filename pscp local_filename user host remote filename with spaces Worse still in a remote to local copy you have to specify the local file name explicitly otherwise PSCP will complain that they don t match unless you specified the unsafe option The following command will give an error message c gt pscp user host oo er warning remote host tried to write to a file called oo er when we requested a file called oo er Instead you need to specify the local file name in full c gt pscp user host oo er oo er If PSCP is using the newer SFTP protocol none of this is a problem and all filenames with spaces in are specified using a single pair of quotes in the obvious way pscp local file user host pscp user host remote file A 7 Troubleshooting A 7 1 Why do I see Incorrect MAC received on packet One possible cause of this that used to be common is a bug in old SSH 2 servers distributed by ssh com This is not the only possible cause see section 10 11 in the documentation Version 2 3 0 and below of their SSH 2 server constructs Message Authentication Codes in the wrong way

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