The Debian GNU/Linux FAQ - The Debian Package Management Tools

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# The Debian GNU/Linux FAQ
Chapter 7 - The Debian Package Management Tools

## 7.1 What programs does Debian provide for managing its packages?

### 7.1.1 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 (see What is a Debian preinst, postinst, prerm, and postrm script?, Section 6.6) script associated with the package.

- Configure a package that already has been unpacked: `dpkg --configure foo`. Among other things, this action runs the postinst (see What is a Debian preinst, postinst, prerm, and postrm script?, Section 6.6) 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 (or regular expression) "foo*": `dpkg --list 'foo*'`.

### 7.1.2 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 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 at any time.

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. The selected "Access Method" is stored after `dselect` exits, so if it does not 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 is 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 (unless the `--expert' command line option was used). Once the user exits the Help screen, he sees the split-screen menu for choosing packages to install (or remove).

  The top part of the screen is a relatively narrow window into the list of Debian's 8250 packages; the bottom part of the screen contains description of the package or group of packages which are highlighted above.

  One can specify which packages should be operated on by highlighting a package name or the label for a group of packages. After that, you can select packages:

  to be installed:
    This is accomplished by pressing the `+' key.
  to be deleted:
    Packages can be deleted two ways:
    - removed: this removes most of the files associated with the package, but preserves the files listed as configuration files (see What is a Debian conffile?, Section 6.5) and package configuration information. This is done by pressing the `-' key.
    - purged: this removes every file that is part of the package. This is done by pressing the `_' key.

    Note that it's not possible to remove "All Packages". If you try that, your system will instead be reduced to the initial installed base packages.

  to be put "on hold"
    This is done by pressing `=', and it 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 is available in the Debian repository you are using (this was specified when you set the Access Method, and acquired when you used Update).

    Just like you can put a package on hold, you can reverse such setting by pressing `:'. That tells `dselect` that the package(s) may be upgraded if a newer version is available. This is the default setting.

  You can select a different order in which the packages are presented, by using the `o' key to cycle between various options for sorting the packages. 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.

  You can also expand meanings of the labels at the top of the screen, 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.

  If you select a package for installation or removal, e.g., `foo.deb`, and that package depends on (or recommends) another package, e.g., `blurf.deb`, then `dselect` will place the you in a sub-screen of the main selection screen. There you 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, you can save your selections and return to the main selection screen by pressing Shift-Q.

- Users returning to the main menu can then select the "Install" menu item to unpack and configure 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; users' selections are preserved by `dselect`.

### 7.1.3 dpkg-deb

This program manipulates Debian archive(`.deb`) files. Some common uses are:

- Find out all the options: `dpkg-deb --help`.

- Determine what files are contained in a Debian archive file: `dpkg-deb --contents foo_VVV-RRR.deb`)

- Extract the files contained in a named Debian archive into a user specified directory: `dpkg-deb --extract 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.

Note that any packages that were merely unpacked using `dpkg-deb --extract` will be incorrectly installed, you should use `dpkg --install` instead.

More information is given in the manual page `dpkg-deb(1)`.

### 7.1.4 apt-get

`apt-get` provides a simple way to install packages from the command line. Unlike `dpkg`, `apt-get` does not understand .deb files, it works with the packages proper name and can only install .deb archives from a source specified in `/etc/apt/sources.list`.

For more information, install `apt` package and read `apt-get(8)`, `sources.list(5)` and `/usr/share/doc/apt/guide.html/index.html`.

### 7.1.5 dpkg-split

This program 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 (i.e. a system containing the `dpkg` package), 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 --split 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 --join "foo*"`.

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

The kernel (filesystem) in Debian GNU/Linux systems supports replacing files even while they're being used.

We also provide a program called `start-stop-daemon` which is used 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 same program is used by installation scripts when a new package containing a daemon is installed, to stop running daemons, and restart them as necessary.

## 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 --list

This prints out a one-line summary for each package, giving a 2-letter status symbol (explained in the header), the package name, the version which is installed, and a brief description.

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

         dpkg --list 'foo*'

To get a more verbose report for a particular package, execute the command:

         dpkg --status packagename

## 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 --search filename`

  This searches for `filename` in installed packages. (This is (currently) equivalent to searching all of the files having the file extension of `.list` in the directory `/var/lib/dpkg/info/`, and adjusting the output to print the names of all the packages containing it, and diversions.)

- `zgrep foo Contents-ARCH.gz`

  This searches for files which contain the substring `foo` in their full path names. The files `Contents-ARCH.gz` (where ARCH represents the wanted architecture) reside in the major package directories (main, non-free, contrib) 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`.

  This method has the advantage over `dpkg --search` in that it will find files in packages that are not currently installed on your system.

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The Debian GNU/Linux FAQ