Running Debian GNU/Linux

This section describes the Debian packaging system and Debian-specific utilities. The Debian/GNU LinuxPackagesfile format is shown in the table on page 65.

Debian distributions come in archives called packages. Every package is a collection of files (programs, usually) that can be installed usingdpkgordselect. In addition, the package contains some information about itself that is read by the installation utilities.

Package classifications. The packages that are included with Debian GNU/Linux are classified according to how essential they are (priority) and their functionality (section).

The priority of a package indicates how essential or necessary it is. Debian GNU/Linux classifies all packages into four different priority levels:

Required. These packages must be installed for the system to operate correctly and have been installed as part of the base system.

Never remove a required package from the system unless you are absolutely sure of 3

what you are doing. This bears repeating: Never, never, never remove a required pack- age from the system unless you are absolutely sure of what you are doing. It is likely that doing so will render your system completely unusable.

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Package Package Name Priority Package Importance

Required Should be installed for proper system operation.

Important Not required but important. Optional Not necessary but useful.

Extra Package may conflict with other packages with higher priorities.

Section General Category

Base Base system. Devel Development tools.

X11 Packages for the X Window System. Admin Administration utilities.

Doc Documentation.

Comm Various communication utilities. Editors Various editors.

Electronics Electronics utilities.

Games Games. (You knew that, didn’t you?) Graphics Graphics utilities.

Hamradio Ytilities for Internet radio. Mail Email clients and servers.

Math Mathematics utilities. (Like calculators, etc.. . . )

Net Various tools to connect to the network (usually TCP/IP).

News Servers and clients for Internet news (NNTP). Shells Shells, such astcshandbash.

Sound Any sound application (like audio CD players).

TeX Anything that can read, write, and convert TEX.

Text Applications to manipulate texts (like

nroff).

Misc Everything else that doesn’t fit above. Maintainer Name of the person who maintains the package and his or her e-mail

address.

Version Version of the package in the format upstream-version–debian-version. Depends A list of other packages upon which the current package depends and

will not function without.

Recommends Another level of package dependencies—it is strongly recommended the packages listed in this field be installed if this package is to be used. Suggests Packages listed in this field may be useful to the packages this entry

describes.

Filename File name of the package via FTP or CD-ROM. MS-DOS-Filename File name of the package in short DOS format. Size Size of the package after the installation.

66 Obtaining and Installing Linux

Important. Important packages are found on almost all UNIX-like operating sys- tems. These packages includecron,man, andvi.

Important packages are abbreviated indselectasImp.

Standard. Standard packages are packages that, more or less, comprise the “stan- dard,” character based, Debian GNU/Linux system. The Standard system includes a fairly complete software development environment and GNU Emacs.

Standard packages are abbreviated indselectasStd.

Optional. Optional packages comprise a fairly complete system. The Optional sys- tem includes TEX and the X Window System.

Optional packages are abbreviated indselectasOpt.

Extra Extra packages are only useful to a small or select group of people, or are installed for a specific purpose. Extra packages might include such programs as electronics and ham radio applications.

Extra packages are abbreviated indselectasXtr.

By default, dselectautomatically selects the Standard system if the user doesn’t want to individually select the packages to be installed.

The section of a package indicates its functionality or use. Packages on the CD-ROM and in FTP archives are arranged in subdirectories according to function. The directory names are fairly self-explanatory: for example, the directoryadmincontains packages for system administration and the directorydevelcontains packages for software develop- ment and programming. Unlike priority levels, there are many sections, and more may be added in the future, so we do not individually describe them in this guide.

Package relationships. Each package includes information about how it relates to the other packages included with the system. There are four package relationships in Debian GNU/Linux: conflicts, dependencies, recommendations, and suggestions.

A conflict occurs when two or more packages cannot be installed on the same system at the same time. A good example of conflicting packages are mail transfer agents (MTAs). A MTA is a program that delivers electronic mail to users on the system and other machines on the network. Debian GNU/Linux has two mail transfer agents:sendmailandsmail. Only one mail transfer agent may be installed at a time. They both do the same job and are not designed to coexist. Therefore, thesendmailandsmailpackages conflict. If you try to installsendmailwhensmailis already installed, the Debian GNU/Linux

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package maintenance system will refuse to install it. Likewise, if you try to installsmail

whensendmailis already installed,dselect(ordpkg; see below) will refuse to install it.

A dependency occurs when one package requires another package to function properly. Using our electronic mail example, users read mail with programs called mail user agents (MUAs). Popular MUAs include elm,pine, andemacsRMAIL mode. It is normal to install several MUAs at once because they do not conflict. But MUAs do not deliver mail—that is the job of the MTA. So all mail user agent packages depend on a mail transfer agent.

A package can also recommend or suggest other related packages.