Wiley Debian GNU/Linux 3.1 Bible
Contents
1. Error Status A single space in this position means there are no errors with the package H Held A package can also be put on hold by the packaging system for instance if its dependencies are broken this often happens when the administrator forces a package s installation ignoring the package s dependencies R Reinst required If a package is in a particularly poor state its reinstallation may be required and this letter indicates that X Both problems When a package is both put on hold by the system and needs to be reinstalled X is the character displayed 80 Part The Fundamentals dpkg can also display which files are part of a given package and search for which package owns a particular file These actions are done using the L and S options respectively The following example illustrates the use of these options user hostname dpkg L base passwd usr usr sbin usr sbin update passwd usr share usr share doc usr share doc base passwd usr share doc base passwd README usr share doc base passwd copyright usr share doc base passwd changelog gz usr share man usr share man man8 usr share man man8 update passwd 8 gz usr share base passwd usr share base passwd group master usr share base passwd passwd master user hostname dpkg S usr share base passwd base passwd usr share base passwd user hostname r Cross dpkg S and dpkg L function only for packages that you2. 88 Part The Fundamentals Setting up mime support 3 26 1 Setting up mutt 1 5 5 1 20040112 1 Setting up libsasl2 modules 2 1 18 2 Reading Package Lists Done Building Dependency Tree Reading extended state information Done hostname Now mutt is installed aptitude installed everything mutt really absolutely required for functioning the Depends and an additional package that mutt s main tainer feels adds a good deal of value the Recommends The other recommended package locales and the package on which mutt depended 11bc6 were already installed As a result neither of them was installed Both of these packages were already installed because they are in the core Debian distribution and are always included in new installs The output from the command should look very much like of apt get s output Not only do apt get and apttiude share a lot of code but they also both end up calling dpkg to do the messy work of installation apt get and aptitude are responsible for selecting and downloading the packages to install to satisfy the various package relationships while dpkg does the heavy lifting Now go ahead and run aptitude without any arguments on the command line to open up a fullscreen session Press to begin a search type el inks and press Enter You should now have the elinks package highlighted To mark the package for installation type The color of the line will chang
3. You can safely leave it at the default After you ve selected which interface you d like to use press Enter You re then asked what priority of questions you d like to see Low priority questions aren t displayed by default they re usually only of interest to obsessive compulsive knob twiddlers like myself selected medium priority questions and you should as well Unlike changing the debconf interface changing which questions are asked will result in subtly differ ent configuration files which may break the instructions given in this book When you re done with this book or when you re familiar with the system as a whole feel free to reconfigure debconf and choose whichever priority level you d like Configuration file handling Configuration files are always handled specially in Debian because they re far more important than most other software files Configuration files are meant to be edited by the administrator and as such may have hours of work put into them Given that and because your installation can break badly if a package blindly overwrites your carefully crafted configuration file extra prompts are displayed whenever something damaging might happen Prompts are displayed whenever 1 A new package is being installed for the first time and there is a preexisting configuration file perhaps copied from an older installation 2 A package is being upgraded but the administrator has manually changed a
4. apt cache policy lt packagename gt will tell you what it is going to do For instance as I write this I get the following report for the KDE word processor kword on a system running sarge with the same sources list as above apt cache policy kword kword Installed 1 1 3 2 l sarge 1 97 98 Part The Fundamentals Candidate 1 1 3 4 Version Table TT 3 4 0 500 http http us debian org sid main Packages 500 http http us debian org etch main Packages IRE 1 1 3 2 l sarge 1 0 100 var 1lib dpkg status 1 1 3 2 1 sarge 1 0 500 http http us debian org sarge main Packages The version numbers may be different by the time you read this but the same principles apply What the output is telling you is that I currently have version 1 1 3 2 1 of kword installed var 1ib dpkg status which is dpkg s database is treated as the source of the package apt has assigned this version a score of 100 Sarge currently has the same version which has a score of 500 as does 1 1 3 4 1 in etch sid kword doesn t exist in experimental As both the versions in sarge and etch sid have the same score the tie is broken by the higher version The number after the version is the priority of the package which is set only if you pin by version see the Installing or keeping a specific version section so it is 0 here etc apt preferences Were I to do an upgrade of kword now the version from testing unstable would
5. configuration file so that it s no longer the same one that was contained in the package Prompts are not displayed when 1 The administrator has removed a configuration file if you want to get a config uration file back from a package you need to purge and reinstall it 2 Anew version of a configuration file exists in the new version of the package and the administrator hasn t changed the current version Chapter 4 Software Management 93 Let s take a working example and reinstall vim If you haven t purged it already do so now with aptitude purge vim This will remove all its configuration files and tell the packaging system that when the package is installed later it should restore the packaged configuration files With vim no longer installed on the system in any way create a fake etc vim vimrc and see what happens when you reinstall it hostname mkdir etc vim hostname echo Testing gt etc vim vimrc hostname cat etc vim vimrec Testing hostname aptitude install vim Reading Package Lists Done Building Dependency Tree Reading extended state information Done The following NEW packages will be installed V 0 packages upgraded 1 newly installed 0 to remove and 61 not upgraded Need to get 774kB of archives After unpacking 1704kB will be used Writing extended state information Done Get 1 http http us debian org sid main vim 1 6 2 426 1 774kB Fetched 774kB in 11s 69 6kB s
6. If there are a number of upgrades available but you want to upgrade only one or more specific packages you can instead use apt get instal and supply it witha package or list of packages on the command line This will upgrade only those pack ages that you ve specified as well as any other upgrades that absolutely must take place to install the newer versions of the packages you ve specified Upgrading using aptitude In terms of upgrading aptitude is used in the exact same way on the command line as apt get However as usual aptitude has a fullscreen interface available as well In the case of upgrades this is particularly useful because it allows you to fine tune which packages get upgraded quickly and easily By default aptitude will mark every package that has a newer available version than the one you ve got installed so simply running aptitude and then pressing the G key to go to the operation summary screen will show you what packages will be upgraded added or removed If you wish to put a package on hold to prevent it from being upgraded press the equal sign key This package will be displayed as being held back every time you go to the operation summary screen and you can decide to upgrade it later just highlight the package and press the plus sign key Integrity Checking Packages To test the validity of your system you may want to verify that the files on your machine match those that were contained in the origin
7. Selecting previously deselected package vim Reading database 17306 files and directories currently installed Unpacking vim from vim_1 3a6 2 426 1_i386 deb Setting up vim 6 2 426 1 o3 tarzo Configuration file etc vim vimrc gt File on system created by you or by a script gt File also in package provided by package maintainer What would you like to do about it Your options are Y or I install the package maintainer s version N or 0 keep your currently installed version D show the differences between the versions Z background this process to examine the situation The default action is to keep your current version xxx vimec Y I N 0 D Z Cdefault N As you can see it s a somewhat ugly looking prompt It s simple and gets the job done however It tells us that there s a configuration file of the same name in the same directory in the package we re installing and that tells us which configuration file it is talking about Your choices at this prompt are simple Press the Y key and press Enter to have the packaged configuration file overwrite your own Press the N key if you know that the file you have is good You can press D to see the differences between the current file and the new file you ll be returned to the prompt after you ve finished reading the differences Lastly if you choose the Z option you re dropped into a shell where you can manually poke
8. be the candidate for installation Because kword 1 1 3 4 1 depends on other packages from testing unstable installing it could inadvertently result in a large part of my system being upgraded to unstable So be very careful in using pinning with com mon library packages such as 1ibc6 which large numbers of packages depend on This can be prevented by creating a file called etc apt preferences with con tents like this Explanation Sarge Package Pin release a stable Pin Priority 999 Explanation Etch Package Pin release a testing Pin Priority 90 Explanation Sid Package Pin release a unstable Pin Priority 80 Package Pin release a experimental Pin Priority 10 Chapter 4 Software Management Each stanza of this file consists of several fields each on their own line Within a stanza fields don t need to be in any particular order however The first field Explanation can be used for comments a short description of what you are trying to do with the pin Package describes which packages are affected by this pin The special value means all packages or you can give one or more package names here The next field contains the criterion you want to use to pick packages to pin In this case the keyword release in the first half of the line means you want to sort packages based on the information in the release file that should accompany each package repository For more information on the sub
9. package management systems there are three main tools that can be used for different purposes at different times The apt family Probably the most famous part of Debian apt get isa command line tool to install and remove packages apt get is part of the apt family of tools where apt stands for advanced package tool apt get s sim plicity is unmatched to install a package you issue a command such as apt get install packagename Though it doesn t provide pretty buttons and lots of colorful icons apt get is easy to learn and simple to use Its com mand line nature also allows it to be used remotely over very low bandwidth or unreliable connections Chapter 4 Software Management YAT apt get however is just one part of the apt family apt cache for example is the apt family s command line search and display tool apt cache shares the same advantages as apt get namely simplicity and ease of use apt setup which was mentioned above is yet another in the family of apt tools aptitude aptitude is a fullscreen console based package management front end browser It s based on the apt libraries meaning that the functional ity provided by the apt family of command line tools is available within apti tude aptitude s strengths lie in its presentation of the data With so many components in the distribution it can be a bit difficult to find exactly what you want Even examining your current system can be a ch
10. with an additional package B then package A must declare that it Recommends the installation of package B The Suggests relationship is a weaker form of the Recommends relationship It s usually used to indicate that some related software can be used alongside the package declaring the relationship When package A absolutely can not exist on the user s machine at the same time as package B package A must declare that it Conflicts with package B When package A provides identical functionality to package B it may declare that it Provides package B Therefore when a package Depends on package B its dependency may be satisfied by package Aor B Occasionally as when a package maintainer is reorganizing a set of closely related packages package A will contain the same files as another package B When this is the case package A declares that it Replaces package B and any files from package A will overwrite files in package B Without this relationship being declared if two packages claim the same file the package management system will produce an error and abort the operation r Cross Reference Chapter 4 Software Management 75 Maintaining package relationships is a large part of a Debian maintainer s job because these relatively simple concepts make software management easy and painless for the user However choosing which relationships to declare with which packages is something of an art Maintain
11. 0 upgraded 0 newly installed 1 to remove and 61 not upgraded Need to get OB of archives After unpacking 1700kB disk space will be freed Do you want to continue Y n y Reading database 17629 files and directories currently installed Removing vim 90 Part The Fundamentals J Note Purging configuration files for vim hostname 1s etc vim ls etc vim No such file or directory hostname apt get again asked us for permission to perform this operation it indicated it was purging the package by appending an asterisk to the package s name The final 1s command verifies that that directory is in fact now gone Now that vim is purged if you reinstall it its default configuration file will be installed freshly again Note however that apt get didn t remove 1 ibgpmg1 which was installed along side vim to satisfy a dependency If packages are installed as dependencies of another package apt get will not look to see whether they are still needed when you uninstall the original package and will simply leave them there Now take a look at how aptitude deals with that scenario Removing and purging packages using aptitude Let s get rid of mutt first which we installed earlier via aptitude hostname aptitude remove mutt Reading Package Lists Done Building Dependency Tree Reading extended state information Done The following packages are unused and will be REMOVED libidnll
12. Software Management T basic unit of software in Debian and indeed in almost every major operating system today is the package A lot of effort goes into making a package that s easy to install and works on the first try Each package needs to declare its relationship to other packages perhaps it needs a library written by another author or a separate program to round out functionality Packages also need to monitor and work with their configuration files to ease upgrades and pre serve changes A large part of administering a system whether by a home user or a paid administrator taking care of thousands of machines is maintaining the software installed on the com puters This chapter provides some basic background on packaging systems in general as well as hands on examples for maintaining software on a Debian system The Anatomy of a Software Package This section reviews the properties common to almost all packaging systems as well as some traits unique to Debian packages Common package properties Everything about a packaging system whether source or binary is designed around standardization and ease of use With the source code available each user is perfectly capable of configuring and compiling building which is not to be con fused with writing his own software but the end result is a very unique machine that can be difficult to administer In This Chapter Package anatomy Debian packa
13. about and perhaps merge the two configuration files by hand ina text editor When you exit the shell you re returned to the prompt 94 Part The Fundamentals Configuration File Handling with ucf The information on configuration file handling in this section refers to regular configuration files the kind that are included in the package normally and aren t generated at install time In that simple case dpkg itself is displaying the prompt and handling the configuration file However pretty much any package that uses debconf scripts also creates a default config uration file on the fly during the package s installation As such the handling is slightly dif ferent ucf emulates the standard dpkg prompt in many ways with the exception that it uses debconf for its user interface The options will be the same and the reasons are the same although the display will look different Since the configuration file you created is fake press Y and press Enter to use the packaged version The installation will complete normally after that Upgrading Packages As mentioned in the introduction of this book sarge users won t be getting updates very often it s a stable release and will only occasionally get a security update However when sarge does get an update it s more than likely a very important fix As such it s important to go through the upgrade process at least once daily to check for upgrades sid users will likely go throug
14. ackaging system to remove the configuration files too so that the next time you install the package you get the default configuration you need to purge the package Removing and purging packages using apt get Once again apt get is a quite simple way to solve this problem Simply run apt get remove packagename and it will remove the package Remove vim as seen in the following session hostname apt get remove vim Reading Package Lists Done Building Dependency Tree Done The following packages will be REMOVED vi 0 packages upgraded 0 newly installed 1 to remove and 0 not upgraded Need to get OB of archives After unpacking 12 2MB will be freed Do you want to continue Y n y Reading database 7567 files and directories currently installed Removing vim dpkg warning while removing vim directory etc vim not empty so not removed hostname apt get will always ask you before it removes a package You ll note that dpkg issued a warning saying that it wasn t able to remove a directory etc vim because it wasn t empty That s not surprising since you just removed the package instead of purging it thus vim s configuration files remain To purge a package pass apt get the purge option hostname 1s etc vim vimrc hostname apt get purge remove vim Reading Package Lists Done Building Dependency Tree Done The following packages will be REMOVED vim
15. al package Almost every package in Debian includes cryptographic signatures for all the files it contains Using the debsums tool you can compare the files on your system against these cryptographic signatures Once you have debsums installed run debsums to see whether any of the files on your system have been modified from the packaged version Since you just did an installation it s very unlikely Typically a file will have changed if you tried to install from source some of the same software you already had installed Ignore any output that warns that some packages don t contain md5sums It s just a warn ing not an error Caution The other reason for wanting to check your files consistency is if you believe your machine s security has been compromised There is no absolute way to ensure that your system hasn t been subverted At best you can confirm that it has been broken into Since the cryptographic signatures contained in Debian packages are stored on your hard drive after the package has been installed an attacker could just as easily modify those signatures to match any modifications they might have made to the system files In the event of a security breach the only option is rein stalling from scratch and copying only nonexecutable files from the old installa tion There are many reasons to do this but I ll leave that to the next chapter Basic System Administration Suffice it to say that if you care about such t
16. all but not necessarily they re the active portion of a given package Debian s packages As I hinted in the previous subsection Debian s package management system is quite advanced It s been evolving for a decade and has been continually refined though that s not to say it s the be all and end all of package management However 74 Part The Fundamentals most users find the most compelling aspect of Debian to be its package manage ment system This subsection discusses its particular properties in detail Package relationships The quality of a package in Debian has a lot to do with how well it declares its rela tionships to other packages and there certainly can be a lot of relationships to declare The full list of package relationships available for a Debian package to declare includes Depends Pre Depends Recommends Suggests Conflicts Provides and Replaces Table 4 1 describes how each of these fields is used Table 4 1 Package Relationships Relationship Field Description and Usage Depends Pre Depends Recommends Suggests Conflicts Provides Replaces If package A requires package B for use by the user or if package B is required for package A to be configured package A must declare that it Depends on package B If package A s installation procedure requires package B package A must declare that it Pre Depends upon package B When package A s functionality is enhanced
17. allation and upgrades a major component of a Debian package is its configuration files Unlike regular files which overwrite old versions or preexisting versions without any prompting on the part of the user configuration files are treated specially A large part of Debian s appeal to system administrators is the care taken to preserve any changes made to a configuration file Preserving changes made to a configuration file isn t easy There are many different configuration file formats and sometimes a single configuration file will have multi ple formats depending on which version of the package you have installed As such there are two standard methods of dealing with configuration files in a Debian package dpkg s conffile handling and a debconf based handler called ucf which stands for update configuration file Dealing with configuration files is presented in detail in the Installing Packages section of this chapter 76 Part The Fundamentals Package repositories Package repositories are large archives of packages that are stored usually on the Internet for users to pull from when they want to install or upgrade software on their system Though obviously not a part of a package repositories are neverthe less very important to the implementation of package management systems Though some package management systems require users to operate directly on package files themselves advanced systems keep da
18. ally numerous default source configuration values that users can should they choose to override This allows for a degree of build time customization that can vary from package to package However most of these systems allow for one notable customization the ability to specify compiler settings Customizing compiler settings allows a greater degree of control over the compilation process which can include performance related optimization Caution There have been many studies conducted on the effect of changing default com piler settings and in almost every common case it proved that the resulting soft ware was slower and more crash prone than software compiled with conservative settings the settings that Debian package maintainers choose by default If you wish to investigate changing compiler settings and rebuilding packages avail your self of the compiler documentation and take some time to research studies that have been done in the field Though source based packaging systems exist and are used by some binary based packaging systems are far more prevalent In these systems the package maintainer configures the source and compiles the software and then packages the result into a simple file which is distributed to the end user Compared to compiling a source package installing a binary package is very fast A large source package can take hours to compile on high end hardware whereas a binary package created from that source c
19. ans that the configuration for programs is stored in configuration files Changing or customizing this type of configuration usually means editing a configu ration file by hand and changing or adding variables and values Debian attempts to make package installation painless and most package maintainers avoid using interactive debconf prompts during a package install but sometimes it s unavoid able If a package can t provide a sensible default configuration file it will instead ask some debconf questions The advantage of debconf is that the user can decide what sorts of questions he d like to see and how to see them Configuring packages using debconf debconf is the standard Debian configuration system Many packages use debconf to provide a single interface to configuration that eliminates the need to have users edit files by instead providing sane defaults and a way to prompt users with ques tions debconf questions are generally asked as part of the package s installation 92 Part The Fundamentals Note but you can also invoke them later on to reconfigure the package This is done by running dpkg reconfigure packagename hostname dpkg reconfigure debconf Reconfiguring debconf allows you to set a variety of parameters used to display and process questions asked via packaged debconf scripts The first question debconf s own configuration script asks is What interface should be used for configuring packages
20. e management bugs do occasionally creep in and interrupt a package installation or removal halfway through Likewise if your computer were Chapter 4 Software Management 79 to lose power during a package maintenance session the database would be left in an inconsistent state There s actually a third space there for another letter which is the error indicator See Table 4 2 for the meanings of the three status letters Table 4 2 Status Indicators Letter Description First Character Desired Status u Unknown For package names that dpkg has never had to install or remove this character is displayed j Install The package is supposed to be installed r Remove The package is supposed to be removed p Purge The package is supposed to be purged removed and with all configuration files deleted as well h Hold Any packages that the administrator has put on hold won t be automatically upgraded or removed Second Character Actual Status n Not Installed The package is not installed i Installed The package is installed c Config files The package s configuration files remain u Unpacked The package has been unpacked and its files have overwritten old ones but the package s post installation script has not been run f Failed config The package s post installation script ran but it failed for some reason h Half installed The package s installation was interrupted Third Character
21. e repository Everything after the URL reflects the components of the repository Though the components you want to add are repository specific there needs to be some text there The examples here refer to a standard Debian package repository for the stable distribution sarge in this case and the main portion of that repository Note Whenever you change anything in etc apt sources list run aptitude E update or apt get update apt Pinning The ability to add multiple sources to etc apt sources 1ist makes it possible to seamlessly integrate unofficial repositories of Debian packages These reposito ries may contain packages not found in Debian or newer or enhanced versions of official packages What happens if the same package exists in two or more repositories As far as the packaging system is concerned it is the same package if it has the same name regardless of the contents By default apt will use the package with the higher ver sion number If two packages have the same version number apt will select the one that best fits your current release that is sarge which in most cases will be the official Debian package If the packages have the same version number and belong to the same release apt will pick the first one it comes across in its database or in other words essentially pick one at random Chapter 4 Software Management Jo amp Sometimes the default is not good enough apt s pinning feature le
22. e system you should try rebuilding the packages instead Summary I covered a lot of material in this chapter running the gamut from packaging con cepts to using unofficial Debian package repositories Having read this chapter you should be perfectly capable of handling software management on your Debian installation including such tasks as finding examining installing removing purg ing configuring and upgrading packages You should also be familiar with the con cept of pinning
23. e to green and in the far left column an i will appear both of these are intended to indicate that the package will be installed when you initiate operations Speaking of initiating operations here s a quick note about aptitude in fullscreen mode You first tell it what you want to do and then you press the G key for go aptitude displays a staging screen showing you what operations it will perform Look over the list of changes and then press G at this staging screen to confirm its actions The screen changes and you can see that aptitude is going to install two extra packages liblua50 and 1iblualib50 to satisfy el inks dependencies Press G a third and final time to begin the installation process When the downloads have completed you ll be asked to confirm for the last time that you want to continue at which point aptitude will call upon dpkg to perform the package installations To reinstall a package with aptitude use either aptitude reinstall packagename or browse to the package in the fullscreen interface and press L to mark the package for reinstallation It will be reinstalled when you next initiate packaging operations Chapter 4 Software Management 89 Removing and Purging Packages In Debian great pains are taken to ensure that configuration data is kept intact When a package is simply removed its configuration files and data are left in place in case you ever want to reinstall the package To tell the p
24. eeping a specific version Sometimes you might want to ensure that a package doesn t get upgraded Maybe you have a local package that you ve tweaked and don t want overwritten with a generic version Or maybe you are relying on the functionality of one particular ver sion of the package Again pinning can help This time the version variant of the pin field is used A specific package name is also used Explanation bash 2 only Package bash Pin version 2 Pin Priority 999 This allows upgrades of any new 2 versions of the bash shell but it keeps you from any nasty surprises when bash 3 comes out This is just an example Usually in Debian packages that are significantly different from their earlier versions are given different names such as bash 3 Note that the comparison of version num bers is done alphabetically not numerically Chapter 4 Software Management 10 1 You can also override version preferences on the apt get command line like this apt get install kword 1 1 3 4 1 And once again this works for package removals too Caution apt pinning is a very powerful tool that gives you a lot of control over the shape of your system but it can be dangerous too The consensus among savvy Debian users is that it should be used very sparingly and certainly not for important sys tem libraries and other core packages If you absolutely must have a newer version of one of those and you just can t upgrade your entir
25. en Type in a single forward slash followed by a single term and then press Enter Pressing the forward 84 Part The Fundamentals Tip slash key tells aptitude that you will be typing in a term to search for This term will be searched for in all packages names aptitude will show your search s first hit To repeat the search again and find subsequent hits press the N key until you find what you re looking for Here s that same process broken down into steps 1 At the prompt type aptitude to start the program user hostname aptitude The main aptitude window should now be displayed 2 Once you are in aptitude type a single forward slash to bring up the search prompt Now type the term you want to search for Press Enter to start the search 3 aptitude will jump to the first package it can find that matches or includes the word you have searched for If this is not the package you are looking for press N to go to the next match Keep repeating until you find a satisfactory package For more information regarding aptitude s searching and filtering capabilities see usr share doc aptitude README 4 Searching using the Debian package Web site All the tools described above work on the package lists stored locally on your com puter This means that they describe only packages that are available on your partic ular architecture for the Debian tree you re using stable testing or sid This is a lot
26. endency Tree Done The following extra packages will be installed libgpmg1 The following NEW packages will be installed libgpmgl vim 0 packages upgraded 2 newly installed 0 to remove and 0 not upgraded eed to get 0B 3796kB of archives After unpacking 12 3MB will be used Do you want to continue LY n y Get 1 http ftp us debian org stable main libgpmg 1 19 6 12 45 2kB Get 2 http ftp us debian org stable main vim 6 1 018 1 3751kB Selecting previously deselected package libgpmgl Reading database 6633 files and directories currently installed Unpacking libgpmgl from libgpmg1_1 19 6 12_i1386 deb Selecting previously deselected package vim Unpacking vim from vim_6 1 018 1_i386 deb Setting up libgpmgl 1 19 6 12 Setting up vim 6 1 018 1 hostname Here you see Debian s dependency resolution at play vim depends on 1ibgpmg1 so that package was marked for installation automatically apt get wanted to be sure that the extra installation was acceptable so it asked for confirmation Then it went ahead and downloaded and installed the packages Pretty simple and that s it To reinstall a package use apt get reinstall install packagename Installing packages using aptitude Before using aptitude you should run aptitude update which has a similar pur pose and effect as running apt get update Alternatively you can press the U key when in apt itude s nor
27. er scripts Debian packages have maintainer scripts which are scripts the package maintainer writes to help ease the installation removal or upgrade of his packages by the user There isn t a single installation script Rather there are five scripts that the main tainer can use although not every package uses every script the pre installation script the post installation script the pre removal script the post removal script and the debconf script These scripts are all run automatically during different por tions of package management operations The names should be self explanatory except for perhaps the debconf script During the installation of your Debian system you were asked a number of ques tions These were done using Debian s configuration framework the self titled debconf debconf scripts primarily serve to collect information from the user to provide a sensible default configuration for a package However debconf scripts are also occasionally used to print messages and warnings to the user Each of the maintainer scripts is provided with a great deal of information about the user s system before they re run including whether the package is being upgraded what version of the package was last installed any errors that might have occurred and so on Configuration files In addition to the regular files that make up the software the declarations of pack age relationships and the maintainer scripts that ease inst
28. example This downloads the latest list of packages from Debian servers and it ensures that you get the latest versions of packages available for the Debian tree you have installed hostname apt get update Hit http ftp us debian org stable main Packages Hit http ftp us debian org stable main Release Hit http ftp us debian org stable main Sources Hit http ftp us debian org stable main Release Get 1 http security debian org stable updates main Packages 183kB Hit http non us debian org stable non US main Packages Hit http non us debian org stable non US main Release Hit http non us debian org stable non US main Sources Hit http non us debian org stable non US main Release Get 2 http security debian org stable updates main Release 1108 Fetched 183kB in 2s 85 7kB s Reading Package Lists Done Building Dependency Tree Done user hostname 86 Part The Fundamentals Tip The output you get won t be identical to the output here but it should be close If you get any errors chances are your etc apt sources 1ist is broken If this is the case go ahead and remove that file with rm etc apt sources 1list and run apt setup to generate a new one Having updated the package list go ahead and install vim vim is an editor a Vi clone but it has far more features hostname apt get install vim Reading Package Lists Done Building Dep
29. ference pinning makes apt cache policy kword kword Installed 1 1 3 2 1 sarge 1 Candidate 1 1 3 2 1 sarge 1 Version Table al 32451 0 80 http http us debian org sid main Packages 90 http http us debian org etch main Packages e 1 1 3 2 1 sarge 1 0 100 var lib dpkg status 1 3 2 1 sarge 1 0 999 http http us debian org sarge main Packages Installing from multiple distributions With pinning set up as shown previously you are protected from accidental upgrades to a different release But what if you want to install a different version of 100 Part The Fundamentals kword You can temporarily override your pinning preferences with apt get s target release option synonyms are t and default release apt get install t testing kword Another method which is handy if you are installing packages from multiple distri butions in the same install session looks like this apt get install kdelibs4 kword testing kdm In this case kdelibs4 and kdm will come from stable while only kword will come from testing These methods can be used to remove packages too Installing from a specific site The origin variant of the pin field in etc apt preferences can be used to ensure packages have a higher priority if they come from a particular place Use a stanza like this Explanation packages from my own site Package Pin origin src braincells com Pin Priority 999 Installing or k
30. fter unpacking 5788kB will be used Do you want to continue Y n y Writing extended state information Done Get 1 http http us debian org sid main libsasl2 2 1 18 2 255kB Get 2 http http us debian org sid main libidnll 0 4 1 1 90 2kB Get 3 http http us debian org sid main libncursesw5 5 4 3 287kB Get 4 http http us debian org sid main mime support 3 26 1 28 6kB Get 5 http http us debian org sid main mutt 1 5 5 1 20040112 1 1375kB Get 6 http http us debian org sid main libsasl2 modules 2 1 18 2 150kB Fetched 2185kB in 9s 230kB s Selecting previously deselected package libsasl2 Reading database 17338 files and directories currently installed Unpacking libsasl2 from libsasl2_2 1 18 2_i1386 deb Selecting previously deselected package libidnll Unpacking libidnll from libidn11_0 4 1 1_i386 deb Selecting previously deselected package libncursesw5 Unpacking libncursesw5 from libncursesw5_5 4 3_i1386 deb Selecting previously deselected package mime support Unpacking mime support from mime support_3 26 1_all deb Selecting previously deselected package mutt Unpacking mutt from mutt_1 5 5 1 20040112 1_i386 deb Selecting previously deselected package libsas l2 modules Unpacking libsasl2 modules from libsasl2 modules_2 1 18 2_i386 deb Setting up libsasl2 2 1 18 2 Setting up libidnll 0 4 1 1 S a gt tting up libncursesw5 5 4 3
31. ges Finding and examining packages Installing packages Removing packages Configuring packages Integrity checking Package repositories apt pinning 72 Part The Fundamentals Source packages versus binary packages A source package is a package that is made up completely of source code Source code is useful for programmers but must be built or compiled before it can actually be run Building packages can take long periods of time even on fast machines and it takes even longer on older and slower machines Binary packages are already compiled and are distributed in a ready to use manner A perennial debate in the GNU Linux world is whether to distribute source packages or binary packages to end users The difference is simple If source packages are distributed the user builds and installs the software on his machine if binary packages are distributed only the installation part is necessary In each case the package system will config ure the source compile it install it and throughout the process run any scripts that are required Compiling a package doesn t necessarily need to be complex There are several source based packaging systems in use and they all make the job of configuring the source package compiling it and installing it relatively pain free In fact this is a basic precept of any packaging system Do as much of the work as possible for the user In the case of source packages there are typic
32. h this upgrading process daily anyway since sid receives updates on a continual basis If you use sid see http people debian org dbharris tracking sid for some helpful tips on upgrading that are specific to sid Whether you use sid or sarge visit http people debian org dbharris check updates for details on getting your Debian system to automatically check for updates and e mail you when any are available Upgrading using apt get As usual before attempting to install or upgrade a package run apt get update to download the latest package lists from the Debian servers After having done so upgrading is as simple as running apt get upgrade apt get upgrade won t by default allow any packages to be removed If there s a case where a package needs to be removed some packages will be held back This is often the case where a package has been renamed the procedure in that case is for apt get to remove the old package and install the new one This is typically a trouble free process per formed automatically but it s always safer to act conservatively If you see a pack age being held back you can instead use apt get dist upgrade which will then allow apt get to satisfy package relationships by removing packages Carefully examine the output however to make sure that nothing you care about is being removed or at least that nothing you care about is being removed without being replaced Chapter 4 Software Management 95
33. have installed See the oe subsection Searching using the Debian package Web site for information on how to look at packages in this manner when you don t have them installed look at packages in thi hen you don t have them installed Using aptitude to list packages As mentioned previously one of apt itude s great strengths is its ability to flexibly display information about your package database The following instructions walk you step by step through an example description of using aptitude 1 Open aptitude with this command user hostname aptitude Your screen should look similar to the one shown in Figure 4 1 As you can see aptitude s main display is nicely organized 2 By default the bottom half of the screen is used to display the long descrip tions of packages Toggle that off by pressing Shift D giving you more real estate to work with in the top half Chapter 4 Software Management 81 Actions Undo Options Views Help Help q Quit u Update g Download Install Remove Pkgs These packages are currently installed on your computer Figure 4 1 aptitude s main display 3 Aside from the categories shown in Figure 4 1 at times others will appear such as New Packages and Upgradeable Packages We re primarily inter ested now in the packages that are currently installed so use the up and down arrow keys to highlight that category and press the Enter key The cate gory will expand into a number of s
34. hings you ll keep your system up to date with respect to any security updates available and closely read all the chapters in this book relating to security 96 Part The Fundamentals Package Repositories and etc apt sources list Although Debian s package repositories are very large and complete they don t quite contain everything The two primary reasons for using unofficial package repositories are to get patent encumbered software or to retrieve newer versions of packages than are available in sarge without using the sid development tree Though specifics differ from repository to repository the general idea is the same add one or more lines to etc apt sources list Since etc apt sources list is the file apt get update and aptitude update read to determine which package lists to download it s worth discussing the makeup of that file Each line describes a single repository and is made up of three parts the binary source keyword the repository s URL and the components within that repository Standard lines look like the following deb http http us debian org debian stable main deb src http http us debian org debian stable main The first word in the line is the binary source indicator deb means the repository contains binary packages you can install and deb src is for source packages Most archives have both binary and source so lines are often added in pairs The second part of the line is simply the URL to th
35. in screen If you decided to explore a bit and view other packages details just keep pressing Q until you re back at the main screen Then press Q one last time to quit and con firm that you wish to quit Using apt cache to show package details Though I really love aptitude it isn t suitable for every purpose For instance the fullscreen nature of the detail view can make it more difficult to use It s also darned near impossible to use apt itude s fullscreen display in a script to automatically retrieve information A good alternative utility is apt cache Take a look at how apt cache displays the ed package s details using the apt cache show command followed by the package name user hostname apt cache show ed Package ed Priority important Section editors Installed Size 144 Maintainer James Troup lt james nocrew org gt Architecture 1386 Version 0 2 20 Chapter 4 Software Management 83 Depends libc6 gt 2 3 1 1 Filename pool main e ed ed_0 2 20_1386 deb Size 44718 MD5sum Oc466ce6al60c62fa558fbbb46a4ea45 Description The classic unix line editor ed is a line oriented text editor It is used to create display modify and otherwise manipulate text files red is a restricted ed it can only edit files in the current directory and cannot execute shell commands user hostname The information apt cache displays is much the same as what aptitude pre sented but it allows for easier sc
36. ither apt get or aptitude Chapter 4 Software Management 85 Installing Packages Now that you know how to find packages you likely want to install some Ill use several example packages one for each tool available First if you aren t logged in as root and you shouldn t be do so now You can either switch to a different con sole with Ctr1 A1lt Fn where n is a number from 1 the first console through 6 Ctr1 Al1t F7 is reserved for X Windows Alternatively you can use the su com mand as in the following user hostname su Password hostname su means super user and it allows you to switch to the root account from a regu lar user account The password you type is the root password which you initially configured during the installation Note the prompt change the terminator is now a pound sign QP instead of a dollar sign indicating that you re logged in as root Since you know you re logged in as root from the pound sign the prompt doesn t include the username at the beginning Installing packages using apt get The simplest is usually the best way to start so let s start with apt get While I recommend aptitude for regular use due mainly to its ability to track automati cally installed packages you can t beat apt get as a learning tool First and fore most before you install any new packages or upgrade old packages with apt get you need to run apt get update as shown in the following code
37. ject see Chapter 27 The sec ond half of the line specifies which field of the release file is to be used a means archive Unfortunately apt doesn t support release code names so you have to use the archive name stable testing unstable instead of sarge etch and sid You can also use c for component such as main contrib or nonfree v for release version such as 3 0 for Debian s woody release o for origin or 1 for label Other keywords you can use in the first half are origin which is confusingly not the same as the origin field in the rel ease file but the Internet address of the package repository such as ftp debian org and version which also is unconnected to the simi larly named field in the release file and instead refers to a package version This will be explained in greater detail further on The last field is the score you want apt to give to this pin By default an installed package gets a score of 100 and any other sources get 500 unless a default release has been specified in apt s configuration in which case packages belonging to that release are assigned 990 In the example preferences file packages belonging to the stable release get the highest priority Testing unstable and experimental are both less than 100 so assuming you have a package installed you will not be prompted to upgrade it even if a newer version is available than what is in stable If yourun apt cache policy again you can see the dif
38. libncursesw5 libsasl2 libsasl2 modules mime support The following packages will be REMOVED mutt 0 packages upgraded 0 newly installed 6 to remove and 61 not upgraded eed to get OB of archives After unpacking 5788kB will be freed Do you want to continue LY n y Writing extended state information Done Reading database 17519 files and directories currently installed Removing mutt Removing libidnll Removing libncursesw5 Removing libsasl2 modules Removing libsasl2 Removing mime support Reading Package Lists Done Building Dependency Tree Reading extended state information Done hostname You can purge a package on the command line with aptitude by running the T command aptitude purge packagename Note the difference between this and apt get which accepts purge as a double dash option to remove Chapter 4 Software Management 9 As you can see the packages that were installed alongside mutt were also removed when you asked for mut t s removal This is because you installed it with aptitude removed it with aptitude and mutt was the only installed package that declared dependencies on these packages If another package had required say mime support the mime support package would have been left intact Unfortunately aptitude can only know whether other packages need a given package You may have after installing a package automatically to satisfy a dependency
39. mal interactive fullscreen mode aptitude can be used in the same way as apt get right on the command line In this example you ll install mutt a common console based e mail client First look at mutt s package relationships more closely using the apt cache show command Chapter 4 Software Management 87 hostname apt cache show mutt grep E Depends Recommends Depends libc6 gt 2 3 2 ds1 4 libidnll libncursesw5 gt 5 3 20030510 1 libsasl2 gt 2 1 15 exim mail transport agent Recommends locales mime support hostname As you can see mutt recommends both the locales and mime support packages locales is installed as part of the basic installation but mime support is not Whereas apt get installs installs only Depends packages by default aptitude will also install recommended packages in the field Recommends as shown in the following code sample hostname aptitude instal mutt Reading Package Lists Done Building Dependency Tree Reading extended state information Done The following NEW packages will be automatically installed libidnll libncursesw5 libsasl2 libsasl2 modules mime support The following NEW packages will be installed libidnll libncursesw5 libsasl2 libsasl2 modules mime support mutt 0 packages upgraded 6 newly installed 0 to remove and 62 not upgraded Need to get 2185kB of archives A
40. ne at all If you provide no arguments dpkg will list all the packages that have records in the database If you provide it with a list of arguments dpkg will interpret it as a list of package names In our example we asked dpkg to list its own information dpkg also supports the use of wildcards as discussed in Chapter 3 to allow you to easily list a set of related packages as in this example ser hostname dpkg 1 base Desired Unknown Install Remove Purge Hold Status Not Installed Config files Unpacked Failed config Half installed Err none Hold Reinst required X both Status Err uppercase bad Name Version Description 44 Sssssesesssass nn sass see esses esses esesssssssssssssssssss n base lt none gt no description available ii base config 1 33 18 Debian base configuration package ii base files 3 0 2 Debian base system miscellaneous files ii base passwd 3 4 1 Debian Base System Password Group Files user hostname Note the double quotes surrounding bas e Without the quotes your shell will inter pret the wildcards itself which might produce unexpected results The last three fields in the output Name Version and Description should be self explanatory The first field however could use a closer examination Those two letters in the first field indicate the state the package should be in and the state the package is actually in Even though Debian goes to great lengths to ensure easy packag
41. nful hand editing of package databases which requires expert knowledge Finding and Examining Packages One of the harder parts of dealing with a Debian system is finding the package you want from among the many available Though finding packages can be difficult it isn t the only sort of information gathering you ll need to use routinely You ll also need to list packages list packaging details determine which files belong to which packages and even occasionally view information about packages available in a dif ferent Debian tree than the one you use This section covers these sorts of tasks 78 Part The Fundamentals Listing installed packages Listing installed packages is a pretty easy task and you can use either dpkg or aptitude to do it Using dpkg to list packages dpkg has a listing mode that doesn t affect the packaging system databases so it s safe to use on a regular basis It can be the most convenient way to quickly see whether a package is installed as you can see with the following shell session ser hostname dpkg 1 dpkg Desired Unknown Instal1l Remove Purge Hold Status Not Installed Config files Unpacked Failed config Half installed Err none Hold Reinst required X both Status Err uppercase bad Name Version Description ii dpkg 1 9 21 Package maintenance system for Debian ser hostname dpkg s 1 option turns on listing mode and you can supply it with a list of argu ments or no
42. ode can be installed in seconds Binary packages also result in a far more consistent end user installation because each end user installs the same binary package Last but certainly not least a binary package maintainer will typi cally be very familiar with the package she is producing and will have in depth knowledge of the ideal compiler and source settings to use Chapter 4 Software Management 73 Binary packages are not without their drawbacks however Notably they tend to require more ancillary software to be installed because disabling the use of this software must be done with the source code In the interests of making the package applicable to the widest audience most of the knobs that control the use of exter nal software are turned all the way up Debian is a binary based distribution It was decided long ago that the tradeoffs for using a binary packaging format far outweighed the added flexibility gained by requiring users to compile each and every bit of software on their system Debian does distribute source packages though Each binary package in Debian that the user installs has an associated source package from which the binary package is built So while Debian s primary means of providing software for installation is via binary packages users who really need to change compile time settings can do so without too much trouble Dependencies Whether dealing with source packages or binary packages another common theme i
43. of packages but it will never be all of them If you are using Debian stable there may be new software that is uploaded only into testing or even sid Occasionally you d like to see what s available anywhere in Debian http packages debian org is the Debian package Web site and it s a great resource for these sorts of situations The most useful sections of the site are the Search package directories and Search the contents of packages windows located toward the bottom of the page Using these tools you can enter a search term and search the complete list of packages in the Debian archive through the archive s Web interface Search package directories functions like apt cache search Search the con tents of packages functions like dpkg S anddpkg L but you don t need to have the package installed on your machine to get results Additionally after clicking on a package s name in the results page you can see other information like the pack age s copyright license and its change log because this information is all provided at the bottom of the page Caution You can but shouldn t download package files from packages debian org and install them manually with dpkg This will not always work though and it can possibly break your system apt get and aptitude do a lot of consistency checking behind the scenes Use packages debian org to find the name of the package you want and then install it with e
44. ore With aptitude you can drill down through the various levels of the system quickly collect ing whatever data you need A special feature specific to aptitude and the reason why I recommend its use is its ability to track packages that were installed automatically As an example say you install package foo During f00 s installation the library bar was installed automatically to satisfy f00 s dependencies When you remove package f 00 library bar will be removed as well so long as no other package still depends on it Tip aptitude can actually be used on the command line as well by providing the same arguments you would give apt get and apt cache So not only does aptitude provide a fullscreen package browser that can often aid in your search ing and system examination but it can also be used with the same simplicity as apt get and apt cache with the added benefit of the tracking of automati cally installed packages dpkg At the bottom of the pile is dpkg Debian s basic package management tool Whenever apt get or aptitude install remove or otherwise operate on a package they re calling dpkg to do the heavy lifting dpkg provides a lower level interface to the packaging system allowing you to override partic ular behaviors These low level package operation interfaces should be used only when you know exactly what you need to do however because making a mistake with dpkg might require some pai
45. ripting Searching with apt cache Finding packages to install can be a tough job but there are a few good options Though aptitude is by far the most flexible allowing for all sorts of search queries and narrowing down of the results apt cache is definitely the easiest to use espe cially for short queries For searching try apt cache s search option as shown in the following example The format is apt cache search one or more search terms This command will search the package names short description and pack age long descriptions and return a list of package names and short one line descrip tions for packages that contain the search term or terms If you get too many results try adding words to the search to narrow it down user hostname apt cache search debian goodies debian goodies Small toolbox style utilities for Debian systems emacs goodies el Miscellaneous add ons for Emacs python An interactive high level object oriented language default version user hostname When you find a package that looks interesting you can use apt cache show as explained in the previous subsection to display the details about a listed package including its long description Searching with aptitude aptitude has great browsing facilities and really flexible searching facilities However the cool stuff is a bit complex so I ll discuss the simplest search method in aptitude Go ahead and run it so that you re at the main scre
46. s dependencies or more generally package relationships Over the years more and more common tasks have been moved into shared libraries code that each devel oper can use instead of writing their own each time Every time this happens a dependency is created Package relationships in their most common form allow a package to declare a dependency on another package A calculator might declare a dependency ona library containing common math functions Graphical applications would declare a dependency on a common graphical user interface toolkit library Though depen dencies as they re called are the most widely understood and implemented pack age relationships they re not the only kind In advanced packaging systems like Debian s packages can also declare a number of other relationships see the list of possible relationships in the Package relationships section of this chapter Installation scripts Aside from containing the software itself as well as declaring any dependencies or other package relationships packages typically include installation scripts These are small programs that act on the user s machine in a fairly intelligent manner These scripts might migrate configuration files to new locations or upgrade configu ration files to new versions They might print a warning telling the user to be care ful with a particularly dangerous piece of software Because these are programs in their own right typically sm
47. started using the package directly so be careful and read apt itude s output before telling it to go ahead with the operation If you want to keep some of those automatically installed packages one way to do it is to use aptitude s fullscreen interactive interface So as usual fire up aptitude Press to start a search type elinks and press Enter el inks should be highlighted To mark a highlighted package for removal press the minus dash key To purge it type in an underscore _ For this exam ple you want to purge elinks so type an underscore You ll note that the line once again changes color this time to purple Press the G key to go to the summary screen and you ll see that both 1iblua50 and 1iblualib50 are also going to be uninstalled Suppose you d like to keep 11b1ua50 around Highlight that package and press the same key you would use to mark a package for installation The color of the line changes back to normal and now 11b1ua50 won t be removed If you want to mark packages as automatically or manually installed highlight the packages and press M or m respectively Press the minus key to mark 11b1ua50 for removal again and then press G to start the operation When you re done quit aptitude Configuring and Configuration Files There are two forms of configuration on a Debian system application specific config uration and debconf based configuration Application specific configuration typi cally me
48. tabases describing the pack ages contained in a repository and can pull from them automatically Not only does this allow the user to retrieve information with only the package name to work with but it also avoids the tedious step of first finding a package file and then downloading it Debian s package repository contains approximately 15 000 binary packages for each architecture it supports The database that describes the packages in this repository is copied to the user s machine on a regular basis by the user in a pro cess described later in this chapter With the database stored locally package searches and information retrieval are fast and convenient The form that a Debian repository takes varies for instance installation CDs are partial repositories However most users prefer using Debian s Internet servers which allow the user to download only those packages they re interested in as opposed to either down loading all 13 CDs worth of packages or purchasing and carrying around a small library of CDs Configuring which Debian repositories to use is as simple as editing etc apt sources list typeman sources list for more information on how to do this or removing etc apt sources 1ist and then running apt setup Package Management Tools Getting into the meat of package management this section simply provides an overview of the various package management tools in Debian In addition to graphi cal front ends and
49. tals Don t quit aptitude yet because we ll examine the ed package in more detail later in this chapter Showing package details Of course performing a package operation whether install remove purge or what have you may require that you understand what the package is and how it works within the system as a whole You can use aptitude or apt cache to see the package details Using aptitude to show package details Examining the package system in detail is where aptitude can really shine Any place where a package name is displayed by aptitude you can press Enter to view that package s details Using the example from the previous section highlight ed and press Enter You re now presented with a new screen detailing all sorts of infor mation about the package Wherever you can highlight a line that starts with three dashes you can press Enter to expand the tree and get more information Go ahead and expand the Packages which depend on ed tree Use the down arrow key to scroll down and you can see all the packages that use ed in some way or another as well as their status again status is indicated in the first field At the bottom of this detailed package display you can see all versions of the package that are avail able sometimes the package has an upgrade available You can press Enter on any of those to view that version s particular details Press the Q key to leave the package detail screen and return to the ma
50. ts you change it Here are a few scenarios where you might want to change the way apt prioritizes upgrades Using selected packages from another release Sometimes you need a newer version of a package on your stable system but you don t want to move entirely to testing or unstable Debian also has an experimental distribution for packages whose state is too raw even for unstable You will want to be very careful about installing and upgrading such packages too careful to trust the computer to do the right thing apt pinning will help in both these and other situations etc apt sources list Start by adding the apt sources for each release to etc apt sources 1ist A file that includes stable testing unstable and experimental will look something like this Debian sarge stable eb http security debian org sarge updates main contrib non free eb http http us debian org debian sarge main contrib non free Debian etch testing eb http http us debian org debian etch main contrib non free Debian sid unstable eb http http us debian org debian sid main contrib non free Debian experimental eb http http us debian org debian experimental main contrib non free After adding these lines run apt get update so apt can add all the packages in these sources to its database You can now install packages from any of these distributions But which will apt get pick apt cache policy The command
51. ubcategories Each package in Debian is assigned a particular category and this listing shows how the results are often displayed 4 Now highlight Editors and press Enter The next lower category level is dis played this is the license level and it allows you to restrict your listing to a particular style of license Packages in the main archive on this level are totally free for use modification and redistribution Though you likely don t see any on your screen packages in the contrib and non free archives have other licensing or use restrictions that may require a careful license examina tion on your part 5 Press Enter to expand the main category You should now see three packages ed nano and nvi These are the only text editors installed on the system by default Examine an example line i ed 0 20 20 0 20 20 The first few characters in the line are equivalent to dpkg s listing mode as is the second field the package name The third field indicates the currently installed version of the package and the fourth field indicates the most recent available version of the package If an upgrade is available for instance the new version of the package is displayed here 6 Highlight the package s line and the bottom line of the screen will display the package s short description You can press Shift D to turn the extended description area back on and view the package s long description 82 Part The Fundamen
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