7. The Debian Package Management Tools

7.1 What program(s) does Debian provide for managing its packages?

dselect

This program is a menu-driven interface to the Debian package management system. It is particularly useful for first-time installations and large-scale upgrades. dselect can

• guide the user as he/she chooses among packages to install or remove, ensuring that no packages are installed that conflict with one another, and that all packages required to make each package work properly are installed;
• warn the user about inconsistencies or incompatibilities in their selections;
• determine the order in which the packages must be installed;
• automatically perform the installation or removal; and
• guide the user through whatever configuration process are required for each package.

dselect begins by presenting the user with a menu of 7 items, each of which is a specific action. The user can select one of the actions by using the arrow keys to move the highlighter bar, then pressing the ENTER key to select the highlighted (highlit?) action.

What the user sees next depends on the action he selected. If he selects any option but Access or Select, then dselect will simply proceed to execute the specified action: e.g., if the user selected the action Remove, then dselect would proceed to remove all of the files selected for removal when the user last chose the Select action.

Both the Access menu item and the Select menu item lead to additional menus. In both cases, the menus are presented as split screens; the top screen gives a scrollable list of choices, while the bottom screen gives a brief explanation ("info") for each choice.

Extensive on-line help is available: Use the '?' key to get to a help screen, then use the '.' key to see each of the several pages of help one screen at a time.

Some users find it easier to navigate dselect when it is colorized. To see color screens in dselect, be sure that you've executed: export TERM=linux before invoking dselect.

The order in which the actions are presented in the first dselect menu represents the order in which a user would normally choose dselect to install packages. However, a user can pick any of the main menu choices as often as needed (including not at all, depending on what one wants to do).

• Begin by choosing an "Access Method". This is the method by which the user plans on accessing Debian packages; e.g., some users have Debian packages available on CD-ROM, while others plan to fetch them using anonymous ftp. (To use the latter approach, a user will have had to fetch and install the package dpkg-ftp before running dselect.) The selected "Access Method" is stored in the file /var/lib/dpkg/cmethopt after dselect exits, so if it doesn't change, then this option need not be invoked again.
• Then "Update" the list of available packages. To do this, dselect reads the file "Packages.gz" which should be included in the top level of the directory where the Debian packages to be installed are stored. (But if it's not there, dselect will offer to make it for you.)
• Select specific packages for installation on his system.

  After choosing this menu item, the user is first presented with a full screen of help; he can exit it (and any help screen) by pressing the SPACEBAR. Better (for first time users) is to read all of the help screen, but repeatedly pressing the '.' key to fetch one page of help after another. Once the user exits the Help screen, he sees the split-screen menu for choosing packages to install (or remove). The top screen is a relatively narrow window into the list of Debian's nearly 500 packages; the bottom screen is a window into "info" about the package or group of packages which are highlighted in the top.

  First-time users are often confused by these aspects of the Select screen:

  • "Deselecting" a packages: One can specify which packages should be removed (previously called "deselecting" an item) by highlighting a package name or the label for a group of packages (e.g., "All") and then pressing either:
    • the '-' key. This removes most of the files associated with the package, but NOT the configuration files, i.e., those listed in /var/lib/dpkg/info/PACKAGENAME.conffiles
    • the '_' key. This removes every file that's part of the package.
    Note that if you "de-select" "All Packages" your system will be reduced to the initial installed base packages. This is probably what you wanted.
  • Putting a package "on hold" (by pressing '='): This effectively tells dselect not to upgrade a package even if the version currently installed on your system is not as recent as the version that's available in the Debian repository you are using (this was specified when you set the Access Method). (The version that's available in the repository is given in the file Packages.gz that's read when the "Update" menu choice is activated.

    Putting a package on "unhold" (by pressing ':'): This is the default, and means that the packages will be upgraded if a newer version is available.

  • The order in which the packages are presented: The default order is to present packages by Priority; within each priority, packages are presented in order of the directory (a.k.a. section) of the archive in which they are stored. Given this sort order, some packages in section A (say) may be presented first, followed by some packages in section B, followed by more packages (of lower priority) in section A. Users can select a different presentation order by using the 'o' key to cycle between various options for sorting the packages.
  • Meanings of the labels at the top of the screen: The labels at the top can be expanded by using the 'v' (verbose) key. This action pushes much of the text that formerly fit onto the display off to the right. To see it, press the right arrow; to scroll back to the left, press the left arrow.
  • What to do with a package conflict/dependency screen: If a user selects (for installation or removal) a package, e.g. foo.deb that depend on or recommend another package, e.g., blurf.deb, then dselect will place the user in a sub-screen of the main selection screen. This process begins by presenting the user with a full-screen Help file, which can be escaped by pressing SPACEBAR. Thereafter, the user can choose among the related packages, accepting the suggested actions (to install or not), or rejecting them. To do the latter, press SHIFT-D; to return to the former, press SHIFT-U. In any case, the user can save his selections and return to the main selection screen by pressing SHIFT-Q.

• Users returning to the main menu can then select either the "Install" menu item, followed by the "Configure" menu item to unpack and then be guided through the configuration files for the selected packages. Alternatively, users wishing to remove files can choose the "Remove" menu item. At any point, users can choose "Quit" to exit dselect; dselect stores users' selections in the file /var/lib/dpkg/status.

dpkg:

This is the main package management program, dpkg can be invoked with many options. Some common uses are:

• Find out all the options: dpkg --help.
• Print out the control file (and other information) for a specified package: dpkg --info foo_VVV-RRR.deb
• Install a package (including unpacking and configuring) onto the file system of the hard disk: dpkg --install foo_VVV-RRR.deb.
• Unpack (but do not configure) a Debian archive into the file system of the hard disk: dpkg --unpack foo_VVV-RRR.deb. Note that this operation does not necessarily leave the package in a usable state; some files may need further customization to run properly. This command removes any already-installed version of the program and runs the preinst script associated with the package.
• Configure a package that's already been unpacked: dpkg --configure foo. Among other things, this action runs the postinst script associated with the package. It also updates the files listed in the conffiles for this package. Notice that the 'configure' operation takes as its argument a package name (e.g., foo), not the name of a Debian archive file (e.g., foo_VVV-RRR.deb).
• Extract a single file named "blurf" (or a group of files named "blurf*" from a Debian archive: dpkg --fsys-tarfile foo_VVV-RRR.deb | tar -xf - blurf*
• Remove a package (but not its configuration files): dpkg --remove foo.
• Remove a package (including its configuration files): dpkg --purge foo.
• List the installation status of packages containing the string 'foo*': dpkg -l foo*.

dpkg-deb

This tool manipulates Debian archive (.deb)files. Some command uses are:

• Find out all the options: dpkg-deb --help.
• Determine what files are contained in a Debian archive file: dpkg-deb -c foo_VVV-RRR.deb)
• Extract the files contained in a named Debian archive into a user specified directory: dpkg-deb -x foo_VVV-RRR.deb tmp extracts each of the files in foo_VVV-RRR.deb into the directory ./tmp. This is convenient for examining the contents of a package in a localized directory, without installing the package into the root file system.

dpkg-split

This Perl script splits large package into smaller files (e.g., for writing onto a set of floppy disks), and can also be used to merge a set of split files back into a single file. It can only be used on a Debian system, since it calls the program dpkg-deb to parse the debian package file into its component records. For example, to split a big .deb file into N parts,

• Execute the command dpkg-split -s foo.deb. This will produce N files each of approximately 460 KBytes long in the current directory.
• Copy those N files to floppy disks.
• Copy the contents of the floppy disks onto the hard disk of your choice on the other machine.
• Join those part-files together using dpkg-split -j "foo*".

7.2 Debian claims to be able to update a running program; how is this accomplished?

Debian GNU/Linux provides a program called the start-stop-daemon which is used by installation scripts to start daemons at boot time or to stop daemons when the kernel runlevel is changed (e.g., from multi-user to single-user or to halt). The start-stop-daemon command is also used when a new package containing a daemon is installed, to stop running daemons, and restart them as necessary, e.g., when a package is being installed with an updated configuration script.

7.3 How can I tell what packages are already installed on a Debian system?

To learn the status of all the packages installed on a Debian system, execute the command: dpkg -l. This prints out a one-line summary for each package, giving a 2-letter status symbol, the package name, the version which is installed, and a very brief description.

To learn the status of packages whose names match the string any pattern beginning with 'foo' by executing the command: dpkg -l "foo*"

To get a more verbose report for a particular package, execute the command: dpkg --status foo.

7.4 How can I find out what package produced a particular file?

To identify the package that produced the file named foo execute either:

• dpkg -S filename.

  This searches through the lists of installed files. This is (currently) equivalent to searching all of the files having the file extension of .list in the directory /var/lib/dpkg/info/.

• grep foo Contents, or zgrep foo Contents.gz.

  This searches for files which contain the substring foo in their full path names. The files Contents and Contents.gz reside in the major package directories (Debian-1.1, non-free, contrib, etc.) at a Debian FTP site. A Contents file refers only to the packages in the subdirectory tree where it resides. Therefore, a user might have to search more than one Contents files to find the package containing the file foo.