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Installing and Using Debian

Presented by David Shea on June 16, 2002

Table of Contents


1. What is Debian?

Debian is a distribution of the GNU/Linux operating system that is
developed and maintained entirely by volunteers. The Debian Project is
committed to freedom, as defined by their social contract
(http://www.debian.org/social_contract). All software in Debian,
as well as all aspects of the distribution itself, may be modified
and redistributed, in source or binary form, free of charge.

Software that does not meet the Debian Free Software Guidelines
(DFSG) but has been configured for use in a Debian system is also
available, though it is not a part of the Debian Project, and
redistribution of these packages may be restricted. The non-free
section of the package archives contains software that does not meet
the requirements of the DFSG, and the contrib section contains packages
that are themselves free, but depend on software that is not.

Though freedom is the raison d’e^tre of the Debian project, it is not
the only reason that people find to use this distribution. The packaging
system has been built in such a way that the entire system may be
upgraded with a minimal amount of effort and while the system is
still running. The large amount of packages available allows for a
wide variety of software to be installed without worrying about how it
will fit with the rest of the system. The "unstable" branch of the
distribution is updated continuously, which allows users to keep up
with the latest in software development while retaining the advantages
of a packaging system. On the other end of the spectrum, the "stable"

branch is extensively tested before release, making it very stable and
secure.


1.1. A quick note on versions

Currently, three branches of the Debian distribution are maintained
at a time: stable, testing, and unstable. Stable is the most recent
official release, and contains packages that have been thoroughly
tested and meet the requirements for stability and security. The only
changes made to the stable branch are to repair security holes and
other critical bugs found after the release. Stable is often accused
of being out of date, since the release schedule tends to be a bit
slow. At the time of this writing, the current stable branch of
Debian is 22 months old.

Unstable contains the most recent available version of every package,
bugs and all.

The testing branch was created after the release of potato as an
attempt to create a compromise between stable and unstable. Packages
are automatically placed in testing from unstable based on activity in
the bug reports (http://bugs.debian.org/). Once the release
manager decides that it’s ready, testing will be renamed to frozen, and
the testing cycles will begin in preparation for a release.

All versions of Debian since 1.1 (buzz) have been named after
characters from the movie Toy Story, and these are usually the names
by which the versions are referred. The current active versions are
potato (2.2, stable), woody (3.0, testing), and sid (unstable).


2. Installing Debian


2.1. How to get debian


2.1.1. cdrom

As with most other Linux distributions, bootable ISO CD images of
the installation files are available for download. At one time there
was a frightening labyrinth of questions that had to be answered
correctly before finally being shown the list of mirrors, in an
attempt to lighten the load on them. Fortunately, this is no more,
and the CD page (http://www.debian.org/CD/) now tells you where
to find the CD images, rather than telling you to buy a CD or perform
some arcane ritual involving the package mirrors and rsync. However,
a full install CD may not be necessary. Unless you are unable to get
your network working during the install, it may be better to download
only enough to boot your system and install the rest over the network.


2.1.2. floppies

There are floppy images available for potato and woody which contain
enough to boot the system, install the kernel and drivers, and install
the rest of the base system through some other means. The base system
is contained in a tarball located in the same directory as the disk
images, and may be automatically downloaded over http or ftp by the
installer, downloaded manually and made available on a local partition or
over nfs, installed from a Debian CD, or installed from another stack
of floppies.

All floppy images are available in
/debian/dists/(potato|woody)/main/disks-arch> in a package mirror,
where arch> is the architecture of the machine on which you wish
to install Debian.


2.1.3. minimal cdrom

For those who loathe making floppies but don’t want or need a full
CD, there is hope. Small CD images containing only the contents of the
rescue, root, and driver floppy images are available from
http://www.debian.org/CD/netinst/ and work well for a network
installation of Debian.


2.2. The install

Though many people curse and say nasty things about the installation
process, it’s actually not too bad. It has gone through several
improvements in usability and stability in the recent past, and most
people will be able to simply walk through the steps in the
installation menu without difficulty. If a shell is needed for any
reason, one can be found on tty2 (accessible with alt-F2), or by
scrolling down the installation menu to "Execute a shell", which will
run a shell on that console and return to the install menu when the
shell exits.

Once the base packages have been installed and a means of booting
the system has been created, you may reboot the system into Debian, at
which point some basic configuration will be handled (root password,
timezone, non-root account), and further package installation will
commence.


3. The Debian Package System

Debian packages are similar to Redhat’s RPMs, with the greatest
difference being a more finely tuned system of dependencies. In addition
to dependencies and conflicts, deb packages have recommended and
suggested packages, which, though not absolutely necessary to install or
run the software in the given package, may be helpful.

The thing that makes Debian packages great, however, is the
Advanced Package Tool, apt. apt is a package management system that
handles downloading, installing, and configuring packages and their
dependencies. Most of the package management tools are actually
frontends to apt.

The only thing that you should need to worry about within apt itself
is the /etc/apt/sources.list file, which tells apt where to find
new packages. The sources.list file is a list of locations of
package archives, in order of preference. The newest available version
of a package will always be used, and if more than one location has
the newest version, the package will be downloaded from the one that
occurs earliest in sources.list.

Each line consists of the type (deb for binary packages, deb-src for
source packages), the location, the version to use (referenced either
by codename (potato, woody, etc) or status (stable, frozen, etc)), and
a list of the branches to use. The current branches are main, contrib,
and non-free, as well as non-US versions of each. Here is an example
sources.list:

# Local package mirror, generated by apt-move
deb file:/var/mirror/debian potato main

deb ftp://ftp-linux.cc.gatech.edu/debian potato main contrib non-free
deb http://www.debian.org/debian potato main contrib non-free

# Packages that can't be exported from the US, usually due to encryption or patents
deb ftp://nonus.debian.org/debian-non-US potato/non-US main contrib non-free

# Source packages for above, so apt-get source pkg-namewill work
deb-src ftp://ftp-linux.cc.gatech.edu/debian potato main contrib non-free
deb-src ftp://ftp.debian.org/debian potato main contrib non-free
deb-src ftp://nonus.debian.org/debian-non-US potato/non-US main contrib non-free

# If a security hole is found in the stable distribution, the fixed version
# of the package will be put here
deb http://security.debian.org/ stable/updates main contrib non-free


3.1. Command line utilities


3.1.1. apt-get

apt-get is the command line interface to apt. With a few simple
commands, it can be used to update the list of available packages,
install and remove individual packages and their dependencies, and
upgrade all the packages in the system to the latest available
version. However, apt-get may not be best for installing packages,
since it ignores the Recommends and Suggests fields, which may
create difficulty in the expected functionality of a package. Suggestions
that apt-get have features added to report recommended and suggested
packages are generally met with claims that apt-get isn’t meant to be
used that way, use some other frontend. Regardless, apt-get is still
useful for many tasks, and it is helpful to at least be familiar with
some of the commands.

update
running ‘apt-get update’ will download the latest package lists from
the locations you put in sources.list, updating the local list of
available packages. It is generally a good idea to run this before
doing anything else.
install package name…>
Installs the packages and any dependencies
remove package name…>
Removes the packages and any packages that depend on them.
Configuration files, if present, will be left behind, so the packages
will be left in the ‘deinstall’ state until purged.
upgrade
Upgrades all packages in the system to the latest version
dist-upgrade
Same as upgrade, but attempts determine changed dependency names
and may be used for upgrading across versions. For example, if you
are running potato and want to run sid instead, you can simply change
all instances of potato in /etc/sources.list to sid and run ‘apt-get
update; apt-get dist-upgrade’ which will upgrade your system with a
minimal amount of trouble.


3.1.2. apt-cache

The full functionality of apt-cache isn’t terribly useful unless you
really enjoy playing around with apt’s package cache, but it can be useful
for finding a particular package name. ‘apt-cache search regex>’
will give a list of all packages with a name that matches the regular
expression, along with a single-line description. ‘apt-cache
depends pkg name…>’ will print out all Dependencies,
Recommendations, and Suggestions for the packages.


3.1.3. apt-move

apt-move is very useful if you run Debian on more than one computer.
It can be used to generate a package archive, usable by other machines,
from the package files downloaded by APT.


3.2. The frontends


3.2.1. tasksel

tasksel is what is run when you choose the "Simple" package selection
method during the initial configuration. There are meta packages
available, named task-*, which contain no data and depend on groups
of other packages. tasksel simply chooses and installs these
task-* packages. However, tasksel cannot be used to uninstall
anything, and can only be used to install whatever the Debian
maintainers felt would make an appropriate group of packages, so it’s
not very useful outside of the initial configuration.


3.2.2. dselect

dselect, the "Advanced" side of the initial package selection, is the
tool that is generally suggested for an everyday package management
tool. It can be used to install, remove, purge, and hold back (package
won’t be upgraded even if newer version is available) individual
packages and dependencies. It notifies the user of recommended and
suggested packages and offers menus to handle situations where more than
one package meets a particular dependency, or to resolve dependency
conflicts. However, it’s extremely slow, has a very user unfriendly
interface, and is impossible to navigate. dselect is single-handedly
responsible for turning countless users away from Debian.


3.2.3. aptitude

aptitude, like dselect, has a curses interface, but, unlike dselect,
it can search through the package database at a reasonable speed, and
its interface is much easier to use. aptitude also allows operations
to be performed on the command line, much like apt-get.


3.2.4. synaptic

synaptic, formerly raptor, is a GUI frontend to apt-get. It is
friendlier (or at least prettier) to use, but suffers from the same
limitations as apt-get. It also has a fairly robust, though slightly
confusing, means of filtering the package list displayed.


3.2.5. stormpkg

Originally created for the now-defunct Stormix, stormpkg is a
GNOME-based APT GUI which can handle full dependency management, package
list filtering based on package name or description to ease the search
for particular packages, and it can edit the sources.list file.
It seems friendly, but still has some stability issues to work
out, like not crashing when someone double-clicks on a package name.


4. Adding to the system.

Once in a while you’ll find some piece of software, or a particular
version of a program, that has no corresponding deb package. What now?
You can either put it in the system as a local addition, or roll your
own deb.

Debian packages will never overwrite anything in /usr/local, so this
is where you should put all software with no corresponding package.
Most of the time, autoconf scripts default to /usr/local as the install
location, so ‘./configure; make; make install’ is often all that is
needed to install a program.

If you do want to make your own package, the easiest way to do this
is usually dh_make, a part of the debhelper system. Start with a regular
source tree, run dh_make from within it, and then you can edit the
control files, preinst and postinst scripts, changelog, and other
package information files. All package files are located in the
debian directory in the source tree. A package can be built by running
debuild from within the source directory. See the policy manual
(http://www.debian.org/doc/debian-policy/) for more information on
package building.


5. Miscellany


5.1. init scripts

Debian uses a System-V init system. Init scripts are marked as
configuration files in packages, so scripts that you add will never be
accidentally overwritten by new packages (at least not without prompting
you first). Init scripts are located in /etc/init.d, and may be added
to the runlevels either by making the symlinks in /etc/rc?.d by hand,
or by using the update-rc.d tool.


5.2. menus

Debian uses a collection of menu configuration files to generate menus
for the various X window managers, so that packages can create menu
entries without needing to know anything about each menu system. Packages
place files in /usr/lib/menu. These files may be overridden globally
by placing files in /etc/menu, or on a per-user basis with files
~/.menu. The menu files are generated from the menu configs by
update-menus. See the documentation to the menu package for more
information on the menu file format. Menu entries may be created for
locally added programs by creating a menu file using the name "local.foo"
for the package name, where foo may be anything. Any local.* package
name is assumed to be always installed.


5.3. kernel modules

modconf allows you to choose modules from a menu, attempt to load
them into the kernel, and then will set things to automatically load
the module on boot. All it does is add the module name to /etc/modules,
and possibly create a file in /etc/modutils if any special options
are needed. The files in /etc/modutils are concatenated together to
form /etc/modules.conf, a task handles by update-modules.


5.4. alternatives

Sometimes more than one program may be installed that handles the
same or similar functions. Debian allows you to choose one of these
to reference by a simple name through the alternatives system. For example,
you may have nvi, elvis, and vim installed on a system, and you
would like to able to type ‘vi’ and run vim. What Debian will do
is create a symlink in /usr/bin/vi to /etc/alternatives/vi, which will in
turn be a symlink to /usr/bin/vim. You can change the mapping of the
alternatives either by changing the symlinks in /etc/alternatives by
hand (the packages will detect when this has happened and not overwrite
them when the packages are updated), or you may use the update-alternatives
program. See the man page for details.


6. Resources

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