As discussed last month, most software packages for Linux are distributed in one of two special file formats: Red Hat Package Manager (RPM) files or Debian (DEB) files. While the previous month focused on working with RPM files, this one spotlights the format and tools used with DEB files.

Debian packages with .deb file extensions store executable files together with configuration files, online documentation, and other information. You can unpack and manipulate these DEB files using the Debian utility dpkg, which is a command-line program that takes many options. A text mode, menu-driven program called dselect is also available for you to manage the packages without having to type dpkg commands. More commonly, you can use a higher-level utility called APT (Advanced Packaging Tool) to work with packages in Debian. For example, instead of downloading a DEB file and installing it with the dpkg command, you can simply use the apt-get command to install the package. The apt-get command can even download the package from an online Debian repository and install it on your system. The dpkg command is still useful when you want to look at the contents of a DEB file that you have manually downloaded from a repository or that might be in the APT cache directory (/var/cache/apt/archives in Debian).

mozilla-firefox_1.0.4-2_i386.deb

The filename has three parts separated by underscores (_):

*  Package name: mozilla-firefox
*  Version and Revision: 1.0.4-2 (Version has two parts separated by a dash. The first part is the package maintainer's version number; the second part is the Debian revision number.)
*  Architecture: i386. (The package is for Intel x86-compatible systems.)
The filename has a .deb extension, which indicates that this is a DEB file.

You can use dpkg to perform a whole lot of operations on packages, but you have to work at a shell prompt in a terminal window or a text console. The format of a dpkg command is

dpkg [options] action package

with zero or more options, an action indicating what dpkg has to do, and the name of a package, a DEB file or a directory (depends on the action argument). Sometimes the dpkg command does not need any name of package or file, just an action.

Here are some examples of actions you can perform with dpkg:

*  Install a package from a DEB file with the command dpkg -i packagefile, where packagefile is the name of the DEB file (for example, vsftpd-*.deb).
*  Remove a package but retain the configuration files with the command dpkg -r packagename, where packagename is the name of the package
*  Configure a package with the command dpkg --configure packagename, where packagenameis the name of a package
*  Purge - remove everything including the configuration files - with the command dpkg -P packagename
*  Audit packages (and find the ones that are partially installed on your system) with the command dpkg -C (does not need a file or package name)
*  List contents of a DEB file with the command dpkg -c packagefile, where packagefile is the name of the DEB file (for example, vsftpd-*.deb)
*  View information about a DEB file with the command dpkg -I packagefile
*  List packages matching pattern with the command dpkg -l pattern, where pattern is the package name pattern - usually with wildcard characters - that you want to match (for example, kernel*)
*  Find packages that contain files with the command dpkg -S pattern, where pattern is the filename pattern - usually with wildcard characters - that the package contains (for example, stdio*)
*  List files installed from a package with the command dpkg -L packagename, where packagename is the name of a package

You can try these commands out on a Debian system or any system that uses DEB packages. For example, to look for all packages matching names that begin with mozilla, type dpkg -l mozilla* in a terminal window. Here is the relevant portion of this command's output on a Debian system:

||/ Name                Version        Description

  +++-==============-==============-============================================

  un  mozilla                     (no  description available)

  un  mozilla-bonobo              (no description available)

  ii  mozilla-browse     1.7.8-1        The Mozilla Internet  application suite - cor

  ii  mozilla-firefo     1.0.4-2        lightweight web browser  based on Mozilla

The ii in the first column indicates that the package is installed; un means the package is not installed.
Another common use of dpkg -l is to list all packages and use grep to find lines that match a search string. For example, to find anything containing kernel, type dpkg -l | grep kernel. If the package names (in the second column of the dpkg -l output) are truncated, adjust the width of the output lines with a command like this:

COLUMNS=132 dpkg -l | grep kernel

TIP: The dpkg -S command is a handy way to locate which package provided a specific file in the system. For example, if you want to figure out what package includes the /etc/host.conf file, type dpkg -S /etc/host.conf and the output shows that the base-files package contains /etc/host.conf:

base-files: /etc/host.conf

dselect is not described in detail, but here are some of the tasks you can perform from the dselect main menu:

*  Specify an access method - how to find the DEB packages
*  Update the list of available packages
*  View the status of installed and available packages
*  Select packages and manage dependencies among packages
*  Install new packages or upgrade existing ones to newer versions
*  Configure packages that are not yet configured
*  Remove packages

One common sequence in dselect is to update the list of available packages and then upgrade all packages for which updates are available. You can, of course, perform that same task with a simple APT command as well.

To install a package with apt-get, simply type apt-get install packagename, where packagename is the name of the package that you want to install. For example, to install the vsftpd package, type apt-get install vsftpd.

Removing a package is equally simple. Type apt-get remove packagename, where packagename is the name of the package you want to remove.

If you want to find the name of a package and you know some terms asso­ciated with the package, you can look for it with the apt-cache utility. For example, to look for a CD/DVD burner package, type apt-cache search burn | more to search through the APT's package cache (which is the list of Debian packages that APT downloads from the servers listed in the /etc/apt/sources.list file). Here are some lines of output from that command:

  arson - KDE frontend for burning CDs
  burn - Command line Data-CD, Audio-CD, ISO-CD, Copy-CD writing  tool
  caca-utils - text  mode graphics utilities
  cdcontrol - A parallel burner that allow you to write to one or  more CD-Writers at once
   cdlabelgen - generates front cards and tray cards for CDs and  DVDs
  cdrtoaster - Tcl/Tk front-end for burning cdrom
  cdw - Tool for burning CDs - console version
  cdw-common - Tool for burning CDs - common files
  cpuburn - a collection of programs to put heavy load on CPU
  cwcdr - Chez Wam CD Ripper
  dvd+rw-tools - DVD+-RW/R tools
  dvdbackup - tool to rip DVDs from the command line
  edenmath.app - Scientific calcualtor for GNUstep
  gcdw - Tool for burning CDs - graphical version
  gcombust - GTK+ based CD mastering and burning program
  ... lines deleted ...

TIP: To search for a keyword that appears in the package's name only, use the --names-only option like this: apt-cache search - -names-only keyword, where keyword is something that appears in the package's name. For example, if you want to find packages that contain selinux in their names, type apt-cache search - -names-only selinux.

You can run apt-get clean periodically to clean out the local repository (in the /var/cache/apt/archives directory) of DEB files that have already been installed. In doing this, you can free up some disk space by removing these DEB files.

Just as last month, this is not a complete list of what can be done with DEB files, but should give you a good understanding of their potential.