<linkhref="ch-software.en.html"rel="chapter"title="5 Software available in the Debian system">
<linkhref="ch-ftparchives.en.html"rel="chapter"title="6 The Debian FTP archives">
<linkhref="ch-pkg_basics.en.html"rel="chapter"title="7 Basics of the Debian package management system">
<linkhref="ch-pkgtools.en.html"rel="chapter"title="8 The Debian package management tools">
<linkhref="ch-uptodate.en.html"rel="chapter"title="9 Keeping your Debian system up-to-date">
<linkhref="ch-kernel.en.html"rel="chapter"title="10 Debian and the kernel">
<linkhref="ch-customizing.en.html"rel="chapter"title="11 Customizing your installation of Debian GNU/Linux">
<linkhref="ch-support.en.html"rel="chapter"title="12 Getting support for Debian GNU/Linux">
<linkhref="ch-contributing.en.html"rel="chapter"title="13 Contributing to the Debian Project">
<linkhref="ch-redistrib.en.html"rel="chapter"title="14 Redistributing Debian GNU/Linux in a commercial product">
<linkhref="ch-nexttime.en.html"rel="chapter"title="15 Changes expected in the next major release of Debian">
<linkhref="ch-faqinfo.en.html"rel="chapter"title="16 General information about the FAQ">
<linkhref="ch-basic_defs.en.html#s-whatisfaq"rel="section"title="1.1 What is this FAQ?">
<linkhref="ch-basic_defs.en.html#s-whatisdebian"rel="section"title="1.2 What is Debian GNU/Linux?">
<linkhref="ch-basic_defs.en.html#s-linux"rel="section"title="1.3 OK, now I know what Debian is... what is Linux?!">
<linkhref="ch-basic_defs.en.html#s-non-linux"rel="section"title="1.4 Does Debian just do GNU/Linux?">
<linkhref="ch-basic_defs.en.html#s-difference"rel="section"title="1.5 What is the difference between Debian GNU/Linux and other Linux distributions? Why should I choose Debian over some other distribution?">
<linkhref="ch-basic_defs.en.html#s-gnu"rel="section"title="1.6 How does the Debian project fit in or compare with the Free Software Foundation's GNU project?">
<linkhref="ch-basic_defs.en.html#s-pronunciation"rel="section"title="1.7 How does one pronounce Debian and what does this word mean?">
<linkhref="ch-getting.en.html#s-version"rel="section"title="2.1 What is the latest version of Debian?">
<linkhref="ch-getting.en.html#s-updatestable"rel="section"title="2.2 Are there package upgrades in `stable'?">
<linkhref="ch-getting.en.html#s-boot-floppies"rel="section"title="2.3 Where/how can I get the Debian installation disks?">
<linkhref="ch-getting.en.html#s-cdrom"rel="section"title="2.4 How do I install the Debian from CD-ROMs?">
<linkhref="ch-getting.en.html#s-cdimage-symlinks"rel="section"title="2.5 Why does the official stable released CD-ROM contain symlinks for `frozen' and `unstable'? I thought this CD contains just `stable'!">
<linkhref="ch-getting.en.html#s-remoteinstall"rel="section"title="2.6 Can I get and install Debian directly from a remote Internet site?">
<linkhref="ch-getting.en.html#s-alternativebootinstaller"rel="section"title="2.7 Are there any alternative strategies for booting the system installer?">
<linkhref="ch-choosing.en.html#s3.1"rel="section"title="3.1 Which Debian distribution (stable/testing/unstable) is better for me?">
<linkhref="ch-choosing.en.html#s3.2"rel="section"title="3.2 But what about Knoppix, Linex, Ubuntu, and others?">
<linkhref="ch-compat.en.html#s-arches"rel="section"title="4.1 On what hardware architectures/systems does Debian GNU/Linux run?">
<linkhref="ch-compat.en.html#s-otherdistribs"rel="section"title="4.2 How compatible is Debian with other distributions of Linux?">
<linkhref="ch-compat.en.html#s-otherunices"rel="section"title="4.3 How source code compatible is Debian with other Unix systems?">
<linkhref="ch-compat.en.html#s-otherpackages"rel="section"title="4.4 Can I use Debian packages (".deb" files) on my Red Hat/Slackware/... Linux system? Can I use Red Hat packages (".rpm" files) on my Debian GNU/Linux system?">
<linkhref="ch-compat.en.html#s-non-debian-programs"rel="section"title="4.5 How should I install a non-Debian program?">
<linkhref="ch-compat.en.html#s-termcap"rel="section"title="4.6 Why can't I compile programs that require libtermcap?">
<linkhref="ch-compat.en.html#s-accelx"rel="section"title="4.7 Why can't I install AccelX?">
<linkhref="ch-compat.en.html#s-motifnls"rel="section"title="4.8 Why do my old XFree 2.1 Motif applications crash?">
<linkhref="ch-software.en.html#s-apps"rel="section"title="5.1 What types of applications and development software are available for Debian GNU/Linux?">
<linkhref="ch-software.en.html#s-softwareauthors"rel="section"title="5.2 Who wrote all that software?">
<linkhref="ch-software.en.html#s-pkglist"rel="section"title="5.3 How can I get a current list of programs that have been packaged for Debian?">
<linkhref="ch-software.en.html#s-buildenv"rel="section"title="5.4 How can I install a developer's environment to build packages?">
<linkhref="ch-software.en.html#s-missing"rel="section"title="5.5 What is missing from Debian GNU/Linux?">
<linkhref="ch-software.en.html#s-no-devs"rel="section"title="5.6 Why do I get "ld: cannot find -lfoo" messages when compiling programs? Why aren't there any libfoo.so files in Debian library packages?">
<linkhref="ch-software.en.html#s-java"rel="section"title="5.7 (How) Does Debian support Java?">
<linkhref="ch-software.en.html#s-isitdebian"rel="section"title="5.8 How can I check that I am using a Debian system, and what version is it?">
<linkhref="ch-software.en.html#s-nonenglish"rel="section"title="5.9 How does Debian support non-English languages?">
<linkhref="ch-software.en.html#s-pine"rel="section"title="5.10 Where is pine?">
<linkhref="ch-software.en.html#s-qmail"rel="section"title="5.11 Where is qmail/ezmlm/djbdns?">
<linkhref="ch-software.en.html#s-flash"rel="section"title="5.12 Where is a player for Flash (SWF)?">
<linkhref="ch-software.en.html#s-googleearth"rel="section"title="5.13 Where is Google Earth?">
<linkhref="ch-software.en.html#s-voip"rel="section"title="5.14 Where is VoIP software?">
<linkhref="ch-software.en.html#s-nonfreewireless"rel="section"title="5.15 I have a wireless network card which doesn't work with Linux. What should I do?">
<linkhref="ch-ftparchives.en.html#s-dists"rel="section"title="6.1 How many Debian distributions are there?">
<linkhref="ch-ftparchives.en.html#s-codenames"rel="section"title="6.2 What are all those names like etch, lenny, etc.?">
<linkhref="ch-ftparchives.en.html#s-sid"rel="section"title="6.3 What about "sid"?">
<linkhref="ch-ftparchives.en.html#s-stable"rel="section"title="6.4 What does the stable directory contain?">
<linkhref="ch-ftparchives.en.html#s-testing"rel="section"title="6.5 What does the testing distribution contain?">
<linkhref="ch-ftparchives.en.html#s-unstable"rel="section"title="6.6 What does the unstable distribution contain?">
<linkhref="ch-ftparchives.en.html#s-dirtree"rel="section"title="6.7 What are all those directories at the Debian FTP archives?">
<linkhref="ch-ftparchives.en.html#s-archsections"rel="section"title="6.8 What are all those directories inside <samp>dists/stable/main</samp>?">
<linkhref="ch-ftparchives.en.html#s-source"rel="section"title="6.9 Where is the source code?">
<linkhref="ch-ftparchives.en.html#s-pools"rel="section"title="6.10 What's in the <samp>pool</samp> directory?">
<linkhref="ch-ftparchives.en.html#s-incoming"rel="section"title="6.11 What is "incoming"?">
<linkhref="ch-ftparchives.en.html#s-ownrepository"rel="section"title="6.12 How do I set up my own apt-able repository?">
<linkhref="ch-pkg_basics.en.html#s-package"rel="section"title="7.1 What is a Debian package?">
<linkhref="ch-pkg_basics.en.html#s-deb-format"rel="section"title="7.2 What is the format of a Debian binary package?">
<linkhref="ch-pkg_basics.en.html#s-pkgname"rel="section"title="7.3 Why are Debian package file names so long?">
<linkhref="ch-pkg_basics.en.html#s-controlfile"rel="section"title="7.4 What is a Debian control file?">
<linkhref="ch-pkg_basics.en.html#s-conffile"rel="section"title="7.5 What is a Debian conffile?">
<linkhref="ch-pkg_basics.en.html#s-maintscripts"rel="section"title="7.6 What is a Debian preinst, postinst, prerm, and postrm script?">
<linkhref="ch-pkg_basics.en.html#s-priority"rel="section"title="7.7 What is an <em>Essential</em>, <em>Required</em>, <em>Important</em>, <em>Standard</em>, <em>Optional</em>, or <em>Extra</em> package?">
<linkhref="ch-pkg_basics.en.html#s-virtual"rel="section"title="7.8 What is a Virtual Package?">
<linkhref="ch-pkg_basics.en.html#s-depends"rel="section"title="7.9 What is meant by saying that a package <em>Depends</em>, <em>Recommends</em>, <em>Suggests</em>, <em>Conflicts</em>, <em>Replaces</em> or <em>Provides</em> another package?">
<linkhref="ch-pkg_basics.en.html#s-pre-depends"rel="section"title="7.10 What is meant by Pre-Depends?">
<linkhref="ch-pkg_basics.en.html#s-pkgstatus"rel="section"title="7.11 What is meant by <em>unknown</em>, <em>install</em>, <em>remove</em>, <em>purge</em> and <em>hold</em> in the package status?">
<linkhref="ch-pkg_basics.en.html#s-puttingonhold"rel="section"title="7.12 How do I put a package on hold?">
<linkhref="ch-pkg_basics.en.html#s-sourcepkgs"rel="section"title="7.13 How do I install a source package?">
<linkhref="ch-pkg_basics.en.html#s-sourcebuild"rel="section"title="7.14 How do I build binary packages from a source package?">
<linkhref="ch-pkg_basics.en.html#s-creatingdebs"rel="section"title="7.15 How do I create Debian packages myself?">
<linkhref="ch-pkgtools.en.html#s-pkgprogs"rel="section"title="8.1 What programs does Debian provide for managing its packages?">
<linkhref="ch-pkgtools.en.html#s-updaterunning"rel="section"title="8.2 Debian claims to be able to update a running program; how is this accomplished?">
<linkhref="ch-pkgtools.en.html#s-whatpackages"rel="section"title="8.3 How can I tell what packages are already installed on a Debian system?">
<linkhref="ch-pkgtools.en.html#s-listfiles"rel="section"title="8.4 How to display the files of a package installed?">
<linkhref="ch-pkgtools.en.html#s-filesearch"rel="section"title="8.5 How can I find out what package produced a particular file?">
<linkhref="ch-pkgtools.en.html#s-datapackages"rel="section"title="8.6 Why doesn't get `foo-data' removed when I uninstall `foo'? How do I make sure old unused library-packages get purged?">
<linkhref="ch-uptodate.en.html#s-howtocurrent"rel="section"title="9.1 How can I keep my Debian system current?">
<linkhref="ch-uptodate.en.html#s-upgradesingle"rel="section"title="9.2 Must I go into single user mode in order to upgrade a package?">
<linkhref="ch-uptodate.en.html#s-savedebs"rel="section"title="9.3 Do I have to keep all those .deb archive files on my disk?">
<linkhref="ch-uptodate.en.html#s-keepingalog"rel="section"title="9.4 How can I keep a log of the packages I added to the system? I'd like to know when which package upgrades and removals have occured!">
<linkhref="ch-uptodate.en.html#s-autoupdate"rel="section"title="9.5 Can I automatically update the system?">
<linkhref="ch-uptodate.en.html#s-aptproxy"rel="section"title="9.6 I have several machines how can I download the updates only one time?">
<linkhref="ch-kernel.en.html#s-non-debian-kernel"rel="section"title="10.1 Can I install and compile a kernel without some Debian-specific tweaking?">
<linkhref="ch-kernel.en.html#s-customkernel"rel="section"title="10.2 What tools does Debian provide to build custom kernels?">
<linkhref="ch-kernel.en.html#s-custombootdisk"rel="section"title="10.3 How can I make a custom boot floppy?">
<linkhref="ch-kernel.en.html#s-modules"rel="section"title="10.4 What special provisions does Debian provide to deal with modules?">
<linkhref="ch-kernel.en.html#s-removeoldkernel"rel="section"title="10.5 Can I safely de-install an old kernel package, and if so, how?">
<linkhref="ch-customizing.en.html#s-papersize"rel="section"title="11.1 How can I ensure that all programs use the same paper size?">
<linkhref="ch-customizing.en.html#s-hardwareaccess"rel="section"title="11.2 How can I provide access to hardware peripherals, without compromising security?">
<linkhref="ch-customizing.en.html#s-consolefont"rel="section"title="11.3 How do I load a console font on startup the Debian way?">
<linkhref="ch-customizing.en.html#s-appdefaults"rel="section"title="11.4 How can I configure an X11 program's application defaults?">
<linkhref="ch-customizing.en.html#s-booting"rel="section"title="11.5 Every distribution seems to have a different boot-up method. Tell me about Debian's.">
<linkhref="ch-customizing.en.html#s-custombootscripts"rel="section"title="11.6 It looks as if Debian does not use <samp>rc.local</samp> to customize the boot process; what facilities are provided?">
<linkhref="ch-customizing.en.html#s-interconffiles"rel="section"title="11.7 How does the package management system deal with packages that contain configuration files for other packages?">
<linkhref="ch-customizing.en.html#s-divert"rel="section"title="11.8 How do I override a file installed by a package, so that a different version can be used instead?">
<linkhref="ch-customizing.en.html#s-localpackages"rel="section"title="11.9 How can I have my locally-built package included in the list of available packages that the package management system knows about?">
<linkhref="ch-customizing.en.html#s-diverse"rel="section"title="11.10 Some users like mawk, others like gawk; some like vim, others like elvis; some like trn, others like tin; how does Debian support diversity?">
<linkhref="ch-support.en.html#s-debiandocs"rel="section"title="12.1 What other documentation exists on and for a Debian system?">
<linkhref="ch-support.en.html#s-onlineresources"rel="section"title="12.2 Are there any on-line resources for discussing Debian?">
<linkhref="ch-support.en.html#s-searchtools"rel="section"title="12.3 Is there a quick way to search for information on Debian GNU/Linux?">
<linkhref="ch-support.en.html#s-buglogs"rel="section"title="12.4 Are there logs of known bugs?">
<linkhref="ch-support.en.html#s-bugreport"rel="section"title="12.5 How do I report a bug in Debian?">
<linkhref="ch-contributing.en.html#s-contrib"rel="section"title="13.1 How can I become a Debian software developer?">
<linkhref="ch-contributing.en.html#s-contribresources"rel="section"title="13.2 How can I contribute resources to the Debian project?">
<linkhref="ch-contributing.en.html#s-supportingorganizations"rel="section"title="13.3 How can I contribute financially to the Debian project?">
<linkhref="ch-redistrib.en.html#s-sellcds"rel="section"title="14.1 Can I make and sell Debian CDs?">
<linkhref="ch-redistrib.en.html#s-packagednonfree"rel="section"title="14.2 Can Debian be packaged with non-free software?">
<linkhref="ch-redistrib.en.html#s-childistro"rel="section"title="14.3 I am making a special Linux distribution for a "vertical market". Can I use Debian GNU/Linux for the guts of a Linux system and add my own applications on top of it?">
<linkhref="ch-redistrib.en.html#s-commercialdebs"rel="section"title="14.4 Can I put my commercial program in a Debian "package" so that it installs effortlessly on any Debian system?">
<linkhref="ch-nexttime.en.html#s-i18n"rel="section"title="15.1 Extended support for non-English users">
<linkhref="ch-nexttime.en.html#s-dependencybasedboot"rel="section"title="15.2 Faster booting: Dependency based boot sequence">
<linkhref="ch-nexttime.en.html#s-di"rel="section"title="15.3 Improvements in the Debian Installer">
<linkhref="ch-nexttime.en.html#s-morearches"rel="section"title="15.4 More architectures">
<linkhref="ch-nexttime.en.html#s-morekernels"rel="section"title="15.5 More kernels">
<linkhref="ch-choosing.en.html#s3.1.1"rel="subsection"title="3.1.1 You asked me to install stable, but in stable so and so hardware is not detected/working. What should I do?">
<linkhref="ch-choosing.en.html#s3.1.2"rel="subsection"title="3.1.2 Will there be different different versions of packages in different distributions?">
<linkhref="ch-choosing.en.html#s3.1.3"rel="subsection"title="3.1.3 The stable distributions really contains outdated packages. Just look at Kde, Gnome, Xorg or even the kernel. They are very old. Why is it so?">
<linkhref="ch-choosing.en.html#s3.1.4"rel="subsection"title="3.1.4 If I were to decide to change to another distribution, Can I do that?">
<linkhref="ch-choosing.en.html#s3.1.5"rel="subsection"title="3.1.5 Could you tell me whether to install testing or unstable?">
<linkhref="ch-choosing.en.html#s3.1.6"rel="subsection"title="3.1.6 You are talking about testing being broken. What do you mean by that?">
<linkhref="ch-choosing.en.html#s3.1.7"rel="subsection"title="3.1.7 Why is it that testing could be broken for months? Wont the fixes introduced in unstable flow directly down into testing?">
<linkhref="ch-choosing.en.html#s3.1.8"rel="subsection"title="3.1.8 From an administrator's point of view, Which distribution requires more attention?">
<linkhref="ch-choosing.en.html#s3.1.9"rel="subsection"title="3.1.9 What happens when a new release is made?">
<linkhref="ch-choosing.en.html#s3.1.10"rel="subsection"title="3.1.10 I have a working Desktop/cluster with Debian installed. How do I know which distribution I am running?">
<linkhref="ch-choosing.en.html#s3.1.11"rel="subsection"title="3.1.11 I am currently tracking stable. Can I change to testing or unstable? If so, How?">
<linkhref="ch-choosing.en.html#s3.1.12"rel="subsection"title="3.1.12 I am currently tracking testing (lenny). What will happen when a release is made? Will I still be tracking testing or will my machine be running the new stable distribution?">
<linkhref="ch-choosing.en.html#s3.1.13"rel="subsection"title="3.1.13 I am still confused. What did you say I should install?">
<linkhref="ch-choosing.en.html#s3.2.1"rel="subsection"title="3.2.1 I know that Knoppix/Linex/Ubuntu/... is Debian-based. So after installing it on the hard disk, can I use 'apt' package tools on it?">
<linkhref="ch-choosing.en.html#s3.2.2"rel="subsection"title="3.2.2 I installed Knoppix/Linex/Ubuntu/... on my hard disk. Now I have a problem. What should I do?">
<linkhref="ch-choosing.en.html#s3.2.3"rel="subsection"title="3.2.3 I'm using Knoppix/Linex/Ubuntu/... and now I want to use Debian. How do I migrate?">
<linkhref="ch-ftparchives.en.html#s-oldcodenames"rel="subsection"title="6.2.1 Which other codenames have been used in the past?">
<linkhref="ch-ftparchives.en.html#s-sourceforcodenames"rel="subsection"title="6.2.2 Where do these codenames come from?">
<linkhref="ch-ftparchives.en.html#s-frozen"rel="subsection"title="6.5.1 What about "testing"? How is it `frozen'?">
Note that <samp>foo</samp> is supposed to be the package name. As a check, one
can learn the package name associated with a particular Debian archive file
(.deb file) in one of these ways:
</p>
<ul>
<li>
<p>
inspect the "Packages" file in the directory where it was stored at a
Debian FTP archive site. This file contains a stanza describing each package;
the first field in each stanza is the formal package name.
</p>
</li>
</ul>
<ul>
<li>
<p>
use the command <samp>dpkg --info foo_VVV-RRR_AAA.deb</samp> (where VVV, RRR
and AAA are the version, revision and architecture of the package in question,
respectively). This displays, among other things, the package name
corresponding to the archive file being unpacked.
</p>
</li>
</ul>
<p>
The <samp>VVV</samp> component is the version number specified by the upstream
developer. There are no standards in place here, so the version number may
have formats as different as "19990513" and "1.3.8pre1".
</p>
<p>
The <samp>RRR</samp> component is the Debian revision number, and is specified
by the Debian developer (or an individual user if he chooses to build the
package himself). This number corresponds to the revision level of the Debian
package, thus, a new revision level usually signifies changes in the Debian
Makefile (<samp>debian/rules</samp>), the Debian control file
(<samp>debian/control</samp>), the installation or removal scripts
(<samp>debian/p*</samp>), or in the configuration files used with the package.
</p>
<p>
The <samp>AAA</samp> component identifies the processor for which the package
was built. This is commonly <samp>i386</samp>, which refers to chips
compatible to Intel's 386 or later versions. For other possibilities review
Debian's FTP directory structure at <a
href="ch-ftparchives.en.html#s-dirtree">What are all those directories at the
Debian FTP archives?, Section 6.7</a>. For details, see the description of
"Debian architecture" in the manual page
<code>dpkg-architecture(1)</code>.
</p>
<hr>
<h2><aname="s-controlfile"></a>7.4 What is a Debian control file?</h2>
<p>
Specifics regarding the contents of a Debian control file are provided in the
Debian Policy Manual, section 5, see <a
href="ch-support.en.html#s-debiandocs">What other documentation exists on and
for a Debian system?, Section 12.1</a>.
</p>
<p>
Briefly, a sample control file is shown below for the Debian package hello:
</p>
<pre>
Package: hello
Priority: optional
Section: devel
Installed-Size: 45
Maintainer: Adam Heath <doogie@debian.org>
Architecture: i386
Version: 1.3-16
Depends: libc6 (>= 2.1)
Description: The classic greeting, and a good example
The GNU hello program produces a familiar, friendly greeting. It
allows nonprogrammers to use a classic computer science tool which
would otherwise be unavailable to them.
.
Seriously, though: this is an example of how to do a Debian package.
It is the Debian version of the GNU Project's `hello world' program
(which is itself an example for the GNU Project).
</pre>
<p>
The Package field gives the package name. This is the name by which the
package can be manipulated by the package tools, and usually similar to but not
necessarily the same as the first component string in the Debian archive file
name.
</p>
<p>
The Version field gives both the upstream developer's version number and (in
the last component) the revision level of the Debian package of this program as
explained in <ahref="#s-pkgname">Why are Debian package file names so long?,
Section 7.3</a>.
</p>
<p>
The Architecture field specifies the chip for which this particular binary was
compiled.
</p>
<p>
The Depends field gives a list of packages that have to be installed in order
to install this package successfully.
</p>
<p>
The Installed-Size indicates how much disk space the installed package will
consume. This is intended to be used by installation front-ends in order to
show whether there is enough disk space available to install the program.
</p>
<p>
The Section line gives the "section" where this Debian package is
stored at the Debian FTP sites.
</p>
<p>
The Priority indicates how important is this package for installation, so that
semi-intelligent software like dselect or aptitude can sort the package into a
category of e.g. packages optionally installed. See <a
href="#s-priority">What is an <em>Essential</em>, <em>Required</em>,
<em>Important</em>, <em>Standard</em>, <em>Optional</em>, or <em>Extra</em>
package?, Section 7.7</a>.
</p>
<p>
The Maintainer field gives the e-mail address of the person who is currently
responsible for maintaining this package.
</p>
<p>
The Description field gives a brief summary of the package's features.
</p>
<p>
For more information about all possible fields a package can have, please see
the Debian Policy Manual, section 5., "Control files and their
fields".
</p>
<hr>
<h2><aname="s-conffile"></a>7.5 What is a Debian conffile?</h2>
<p>
Conffiles is a list of configuration files (usually placed in
<samp>/etc</samp>) that the package management system will not overwrite when
the package is upgraded. This ensures that local values for the contents of
these files will be preserved, and is a critical feature enabling the in-place
upgrade of packages on a running system.
</p>
<p>
To determine exactly which files are preserved during an upgrade, run:
</p>
<pre>
dpkg --status package
</pre>
<p>
And look under "Conffiles:".
</p>
<hr>
<h2><aname="s-maintscripts"></a>7.6 What is a Debian preinst, postinst, prerm, and postrm script?</h2>
<p>
These files are executable scripts which are automatically run before or after
a package is installed. Along with a file named <samp>control</samp>, all of
these files are part of the "control" section of a Debian archive
file.
</p>
<p>
The individual files are:
</p>
<dl>
<dt>preinst</dt>
<dd>
<p>
This script executes before that package will be unpacked from its Debian
archive (".deb") file. Many 'preinst' scripts stop services for
packages which are being upgraded until their installation or upgrade is
completed (following the successful execution of the 'postinst' script).
</p>
</dd>
</dl>
<dl>
<dt>postinst</dt>
<dd>
<p>
This script typically completes any required configuration of the package
<samp>foo</samp> once <samp>foo</samp> has been unpacked from its Debian
archive (".deb") file. Often, 'postinst' scripts ask the user for
input, and/or warn the user that if he accepts default values, he should
remember to go back and re-configure that package as the situation warrants.
Many 'postinst' scripts then execute any commands necessary to start or restart
a service once a new package has been installed or upgraded.
</p>
</dd>
</dl>
<dl>
<dt>prerm</dt>
<dd>
<p>
This script typically stops any daemons which are associated with a package.
It is executed before the removal of files associated with the package.
</p>
</dd>
</dl>
<dl>
<dt>postrm</dt>
<dd>
<p>
This script typically modifies links or other files associated with
<samp>foo</samp>, and/or removes files created by the package. (Also see <a
href="#s-virtual">What is a Virtual Package?, Section 7.8</a>.)
</p>
</dd>
</dl>
<p>
Currently all of the control files can be found in directory
<samp>/var/lib/dpkg/info</samp>. The files relevant to package
<samp>foo</samp> begin with the name "foo" and have file extensions
of "preinst", "postinst", etc., as appropriate. The file
<samp>foo.list</samp> in that directory lists all of the files that were
installed with the package <samp>foo</samp>. (Note that the location of these
files is a dpkg internal; you should not rely on it.)
</p>
<hr>
<h2><aname="s-priority"></a>7.7 What is an <em>Essential</em>, <em>Required</em>, <em>Important</em>, <em>Standard</em>, <em>Optional</em>, or <em>Extra</em> package?</h2>
<p>
Each Debian package is assigned a <em>priority</em> by the distribution
maintainers, as an aid to the package management system. The priorities are:
</p>
<ul>
<li>
<p>
<strong>Required</strong>: packages that are necessary for the proper
functioning of the system.
</p>
<p>
This includes all tools that are necessary to repair system defects. You must
not remove these packages or your system may become totally broken and you may
probably not even be able to use dpkg to put things back. Systems with only
the Required packages are probably unusable, but they do have enough
functionality to allow the sysadmin to boot and install more software.
</p>
</li>
</ul>
<ul>
<li>
<p>
<strong>Important</strong> packages should be found on any Unix-like system.
</p>
<p>
Other packages which the system will not run well or be usable without will be
here. This does <em>NOT</em> include Emacs or X or TeX or any other large
applications. These packages only constitute the bare infrastructure.
</p>
</li>
</ul>
<ul>
<li>
<p>
<strong>Standard</strong> packages are standard on any Linux system, including
a reasonably small but not too limited character-mode system. Tools are
included to be able to browse the web (using w3m), send e-mail (with mutt) and
download files from FTP servers.
</p>
<p>
This is what will install by default if users do not select anything else. It
does not include many large applications, but it does include the Python
interpreter and some server software like OpenSSH (for remote administration),
Exim (for mail delivery, although it can be configured for local delivery
only), an identd server (pidentd) and the RPC portmapper
(<samp>portmap</samp>). It also includes some common generic documentation
that most users will find helpful.
</p>
</li>
</ul>
<ul>
<li>
<p>
<strong>Optional</strong> packages include all those that you might reasonably
want to install if you did not know what it was, or do not have specialized
requirements.
</p>
<p>
This includes X, a full TeX distribution, and lots of applications.
</p>
</li>
</ul>
<ul>
<li>
<p>
<strong>Extra</strong>: packages that either conflict with others with higher
priorities, are only likely to be useful if you already know what they are, or
have specialized requirements that make them unsuitable for
"Optional".
</p>
</li>
</ul>
<p>
If you do a default Debian installation all the packages of priority
<strong>Standard</strong> or higher will be installed in your system. If you
select pre-defined tasks you will get lower priority packages too.
</p>
<p>
Additionally, some packages are marked as <strong>Essential</strong> since they
are absolutely necessary for the proper functioning of the system. The package
management tools will refuse to remove these.
</p>
<hr>
<h2><aname="s-virtual"></a>7.8 What is a Virtual Package?</h2>
<p>
A virtual package is a generic name that applies to any one of a group of
packages, all of which provide similar basic functionality. For example, both
the <samp>tin</samp> and <samp>trn</samp> programs are news readers, and should
therefore satisfy any dependency of a program that required a news reader on a
system, in order to work or to be useful. They are therefore both said to
provide the "virtual package" called <samp>news-reader</samp>.
</p>
<p>
Similarly, <samp>smail</samp> and <samp>sendmail</samp> both provide the
functionality of a mail transport agent. They are therefore said to provide
the virtual package, "mail transport agent". If either one is
installed, then any program depending on the installation of a
<samp>mail-transport-agent</samp> will be satisfied by the existence of this
virtual package.
</p>
<p>
Debian provides a mechanism so that, if more than one package which provide the
same virtual package is installed on a system, then system administrators can
set one as the preferred package. The relevant command is
<samp>update-alternatives</samp>, and is described further in <a
href="ch-customizing.en.html#s-diverse">Some users like mawk, others like gawk;
some like vim, others like elvis; some like trn, others like tin; how does
Debian support diversity?, Section 11.10</a>.
</p>
<hr>
<h2><aname="s-depends"></a>7.9 What is meant by saying that a package <em>Depends</em>, <em>Recommends</em>, <em>Suggests</em>, <em>Conflicts</em>, <em>Replaces</em> or <em>Provides</em> another package?</h2>
<p>
The Debian package system has a range of package "dependencies" which
are designed to indicate (in a single flag) the level at which Program A can
operate independently of the existence of Program B on a given system:
</p>
<ul>
<li>
<p>
Package A <em>depends</em> on Package B if B absolutely must be installed in
order to run A. In some cases, A depends not only on B, but on a version of B.
In this case, the version dependency is usually a lower limit, in the sense
that A depends on any version of B more recent than some specified version.
</p>
</li>
</ul>
<ul>
<li>
<p>
Package A <em>recommends</em> Package B, if the package maintainer judges that
most users would not want A without also having the functionality provided by
B.
</p>
</li>
</ul>
<ul>
<li>
<p>
Package A <em>suggests</em> Package B if B contains files that are related to
(and usually enhance) the functionality of A.
</p>
</li>
</ul>
<ul>
<li>
<p>
Package A <em>conflicts</em> with Package B when A will not operate if B is
installed on the system. Most often, conflicts are cases where A contains
files which are an improvement over those in B. "Conflicts" are
often combined with "replaces".
</p>
</li>
</ul>
<ul>
<li>
<p>
Package A <em>replaces</em> Package B when files installed by B are removed and
(in some cases) over-written by files in A.
</p>
</li>
</ul>
<ul>
<li>
<p>
Package A <em>provides</em> Package B when all of the files and functionality
of B are incorporated into A. This mechanism provides a way for users with
constrained disk space to get only that part of package A which they really
need.
</p>
</li>
</ul>
<p>
More detailed information on the use of each these terms can be found in the
Policy manual.
</p>
<hr>
<h2><aname="s-pre-depends"></a>7.10 What is meant by Pre-Depends?</h2>
<p>
"Pre-Depends" is a special dependency. In the case of most packages,
<samp>dpkg</samp> will unpack its archive file (i.e., its <samp>.deb</samp>
file) independently of whether or not the files on which it depends exist on
the system. Simplistically, unpacking means that <samp>dpkg</samp> will
extract the files from the archive file that were meant to be installed on your
file system, and put them in place. If those packages <em>depend</em> on the
existence of some other packages on your system, <samp>dpkg</samp> will refuse
to complete the installation (by executing its "configure" action)
until the other packages are installed.
</p>
<p>
However, for some packages, <samp>dpkg</samp> will refuse even to unpack them
until certain dependencies are resolved. Such packages are said to
"Pre-depend" on the presence of some other packages. The Debian
project provided this mechanism to support the safe upgrading of systems from
<samp>a.out</samp> format to <samp>ELF</samp> format, where the <em>order</em>
in which packages were unpacked was critical. There are other large upgrade
situations where this method is useful, e.g. the packages with the required
priority and their LibC dependency.
</p>
<p>
As before, more detailed information about this can be found in the Policy
manual.
</p>
<hr>
<h2><aname="s-pkgstatus"></a>7.11 What is meant by <em>unknown</em>, <em>install</em>, <em>remove</em>, <em>purge</em> and <em>hold</em> in the package status?</h2>
<p>
These "want" flags tell what the user wanted to do with a package (as
indicated either by the user's actions in the "Select" section of
<samp>dselect</samp>, or by the user's direct invocations of
<samp>dpkg</samp>).
</p>
<p>
Their meanings are:
</p>
<ul>
<li>
<p>
unknown - the user has never indicated whether he wants the package
</p>
</li>
</ul>
<ul>
<li>
<p>
install - the user wants the package installed or upgraded
</p>
</li>
</ul>
<ul>
<li>
<p>
remove - the user wants the package removed, but does not want to remove any
existing configuration files.
</p>
</li>
</ul>
<ul>
<li>
<p>
purge - the user wants the package to be removed completely, including its
configuration files.
</p>
</li>
</ul>
<ul>
<li>
<p>
hold - the user wants this package not to be processed, i.e., he wants to keep
the current version with the current status whatever that is.
</p>
</li>
</ul>
<hr>
<h2><aname="s-puttingonhold"></a>7.12 How do I put a package on hold?</h2>
<p>
There are three ways of holding back packages, with dpkg, aptitude or with
dselect.
</p>
<p>
With dpkg, you have to export the list of package selections, with:
</p>
<pre>
dpkg --get-selections \* > selections.txt
</pre>
<p>
Then edit the resulting file <code>selections.txt</code>, change the line
containing the package you wish to hold, e.g. <code>libc6</code>, from this:
</p>
<pre>
libc6 install
</pre>
<p>
to this:
</p>
<pre>
libc6 hold
</pre>
<p>
Save the file, and reload it into dpkg database with:
</p>
<pre>
dpkg --set-selections < selections.txt
</pre>
<p>
With aptitude, you can hold a package using
</p>
<pre>
aptitude hold package_name
</pre>
<p>
and remove the hold with
</p>
<pre>
aptitude unhold package_name
</pre>
<p>
With dselect, you have to enter the [S]elect screen, find the package you wish
to hold in its present state, and press the `=' key (or `H'). The changes will
go live immediately after you exit the [S]elect screen.
</p>
<hr>
<h2><aname="s-sourcepkgs"></a>7.13 How do I install a source package?</h2>
<p>
Debian source packages can't actually be "installed", they are just
unpacked in whatever directory you want to build the binary packages they
produce.
</p>
<p>
Source packages are distributed on most of the same mirrors where you can
obtain the binary packages. If you set up your APT's
<code>sources.list(5)</code> to include the appropriate "deb-src"
lines, you'll be able to easily download any source packages by running
</p>
<pre>
apt-get source foo
</pre>
<p>
To help you in actually building the source package, Debian source package
provide the so-called build-dependencies mechanism. This means that the source
package maintainer keeps a list of other packages that are required to build
their package. To see how this is useful, run
</p>
<pre>
apt-get build-dep foo
</pre>
<p>
before building the source.
</p>
<hr>
<h2><aname="s-sourcebuild"></a>7.14 How do I build binary packages from a source package?</h2>
<p>
The preferred way to do this is by using various wrapper tools. We'll show how
it's done using the <samp>devscripts</samp> tools. Install this package if you
haven't done so already.
</p>
<p>
Now, first get the source package:
</p>
<pre>
apt-get source foo
</pre>
<p>
and change to the source tree:
</p>
<pre>
cd foo-*
</pre>
<p>
Then install needed build-dependencies (if any):
</p>
<pre>
sudo apt-get build-dep foo
</pre>
<p>
Then create a dedicated version of your own build (so that you won't get
confused later when Debian itself releases a new version)
</p>
<pre>
dch -l local 'Blah blah blah'
</pre>
<p>
And finally build your package
</p>
<pre>
debuild -us -uc
</pre>
<p>
If everything worked out fine, you should now be able to install your package
by running
</p>
<pre>
sudo dpkg -i ../*.deb
</pre>
<p>
If you prefer to do things manually, and don't want to use
<samp>devscripts</samp>, follow this procedure:
</p>
<p>
You will need all of foo_*.dsc, foo_*.tar.gz and foo_*.diff.gz to compile the
source (note: there is no .diff.gz for some packages that are native to
Debian).
</p>
<p>
Once you have them (<ahref="#s-sourcepkgs">How do I install a source package?,
Section 7.13</a>), if you have the <code>dpkg-dev</code> package installed, the
following command:
</p>
<pre>
dpkg-source -x foo_version-revision.dsc
</pre>
<p>
will extract the package into a directory called <samp>foo-version</samp>.
</p>
<p>
If you want just to compile the package, you may cd into
<samp>foo-version</samp> directory and issue the command
</p>
<pre>
dpkg-buildpackage -rfakeroot -b
</pre>
<p>
to build the package (note that this also requires the <code>fakeroot</code>
package), and then
</p>
<pre>
dpkg -i ../foo_version-revision_arch.deb
</pre>
<p>
to install the newly-built package(s).
</p>
<hr>
<h2><aname="s-creatingdebs"></a>7.15 How do I create Debian packages myself?</h2>
<p>
For a more detailed description on this, read the New Maintainers' Guide,
available in the <code>maint-guide</code> package, or at <code><a
