The Debian GNU/Linux FAQ
Chapter 10 - Customizing your installation of Debian GNU/Linux
10.1 How can I ensure that all programs use the same paper size?
Install the libpaperg package, and it will ask you for a
system-wide default paper size. This setting will be kept in the file
/etc/papersize.
Users can override the paper size setting using the PAPERSIZE
environment variable. For details, see the manual page
papersize(5).
10.2 How can I provide access to hardware peripherals, without compromising security?
Many device files in the /dev directory belong to some predefined
groups. For example, /dev/fd0 belongs to the floppy
group, and /dev/dsp belongs to the audio group.
If you want a certain user to have access to one of these devices, just add the
user to the group the device belongs to, i.e. do:
adduser user group
This way you won't have to chmod the device file.
10.3 How do I load a console font on startup the Debian way?
The kbd and console-tools packages support this, edit
/etc/kbd/config or /etc/console-tools/config files.
10.4 How can I configure an X11 program's application defaults?
Debian's X programs will install their application resource data in the
/etc/X11/app-defaults/ directory. If you want to customize X
applications globally, put your customizations in those files. They are marked
as configuration files, so their contents will be preserved during upgrades.
10.5 Every distribution seems to have a different boot-up method. Tell me about Debian's.
Like all Unices, Debian boots up by executing the program init.
The configuration file for init (which is
/etc/inittab) specifies that the first script to be executed
should be /etc/init.d/rcS. This script checks and mounts file
systems, loads modules, starts the network services, sets the clock, performs
other initialization, and then runs all of the scripts (except those with a `.'
in the filename) in /etc/rc.boot/. Any scripts in the latter
directory are usually reserved for system administrator use, and using them in
packages is deprecated.
After completing the boot process, init executes all start scripts
in a directory specified by the default runlevel (this runlevel is given by the
entry for id in /etc/inittab). Like most System V
compatible Unices, Linux has 7 runlevels:
0 (halt the system),
1 (single-user mode),
2 through 5 (various multi-user modes), and
6 (reboot the system).
Debian systems come with id=2, which indicates that the default runlevel will
be '2' when the multi-user state is entered, and the scripts in
/etc/rc2.d/ will be run.
In fact, the scripts in any of the directories, /etc/rcN.d/ are
just symbolic links back to scripts in /etc/init.d/. However, the
names of the files in each of the /etc/rcN.d/ directories
are selected to indicate the way the scripts in
/etc/init.d/ will be run. Specifically, before entering any
runlevel, all the scripts beginning with 'K' are run; these scripts kill
services. Then all the scripts beginning with 'S' are run; these scripts start
services. The two-digit number following the 'K' or 'S' indicates the order in
which the script is run. Lower numbered scripts are executed first.
This approach works because the scripts in /etc/init.d/ all take
an argument which can be either `start', `stop', `reload', `restart' or
`force-reload' and will then do the task indicated by the argument. These
scripts can be used even after a system has been booted, to control various
processes.
For example, with the argument `reload' the command
/etc/init.d/sendmail reload
sends the sendmail daemon a signal to reread its configuration file.
10.6 It looks as if Debian does not use rc.local to customize the boot process; what facilities are provided?
Suppose a system needs to execute script foo on start-up, or on
entry to a particular (System V) runlevel. Then the system administrator
should:
Enter the script foo into the directory /etc/init.d/.
Run the Debian command update-rc.d with appropriate arguments, to
set up links between the (command-line-specified) directories rc?.d and
/etc/init.d/foo. Here, '?' is a number from 0 through 6 and
corresponds to each of the System V runlevels.
Reboot the system.
The command update-rc.d will set up links between files in the
directories rc?.d and the script in /etc/init.d/. Each link will
begin with a 'S' or a 'K', followed by a number, followed by the name of the
script. Scripts beginning with 'S' in /etc/rcN.d/ are executed
when runlevel N is entered. Scripts beginning with a 'K' are
executed when leaving runlevel N.
One might, for example, cause the script foo to execute at
boot-up, by putting it in /etc/init.d/ and installing the links
with update-rc.d foo defaults 19. The argument 'defaults' refers
to the default runlevels, which are 2 through 5. The argument '19' ensures
that foo is called before any scripts containing numbers 20 or
larger.
10.7 How does the package management system deal with packages that contain configuration files for other packages?
Some users wish to create, for example, a new server by installing a group of
Debian packages and a locally generated package consisting of configuration
files. This is not generally a good idea, because dpkg will not
know about those configuration files if they are in a different package, and
may write conflicting configurations when one of the initial "group"
of packages is upgraded.
Instead, create a local package that modifies the configuration files of the
"group" of Debian packages of interest. Then dpkg and
the rest of the package management system will see that the files have been
modified by the local "sysadmin" and will not try to overwrite them
when those packages are upgraded.
10.8 How do I override a file installed by a package, so that a different version can be used instead?
Suppose a sysadmin or local user wishes to use a program
"login-local" rather than the program "login" provided by
the Debian login package.
Do not:
Overwrite /bin/login with login-local.
The package management system will not know about this change, and will simply
overwrite your custom /bin/login whenever login (or
any package that provides /bin/login) is installed or updated.
Rather, do
Execute:
dpkg-divert --divert /bin/login.debian /bin/login
in order to cause all future installations of the Debian login
package to write the file /bin/login to
/bin/login.debian instead.
Then execute:
cp login-local /bin/login
to move your own locally-built program into place.
Details are given in the manual page dpkg-divert(8).
10.9 How can I have my locally-built package included in the list of available packages that the package management system knows about?
BIN-DIR is a directory where Debian archive files (which usually have an
extension of ".deb") are stored.
OVERRIDE_FILE is a file that is edited by the distribution maintainers and is
usually stored on a Debian FTP archive at indices/override.main.gz
for the Debian packages in the "main" distribution. You can ignore
this for local packages.
PATHPREFIX is an optional string that can be prepended to the
my_Packages file being produced.
Once you have built the file my_Packages, tell the package
management system about it by using the command:
dpkg --merge-avail my_Packages
If you are using APT, you can add the local repository to your
sources.list(5) file, too.
10.10 Some users like mawk, others like gawk; some like vim, others like elvis; some like trn, others like tin; how does Debian support diversity?
There are several cases where two packages provide two different versions of a
program, both of which provide the same core functionality. Users might prefer
one over another out of habit, or because the user interface of one package is
somehow more pleasing than the interface of another. Other users on the same
system might make a different choice.
Debian uses a "virtual" package system to allow system administrators
to choose (or let users choose) their favorite tools when there are two or more
that provide the same basic functionality, yet satisfy package dependency
requirements without specifying a particular package.
For example, there might exist two different versions of newsreaders on a
system. The news server package might 'recommend' that there exist
some news reader on the system, but the choice of tin or
trn is left up to the individual user. This is satisfied by
having both the tin and trn packages provide the
virtual package news-reader. Which program is invoked is
determined by a link pointing from a file with the virtual package name
/etc/alternatives/news-reader to the selected file, e.g.,
/usr/bin/trn.
A single link is insufficient to support full use of an alternate program;
normally, manual pages, and possibly other supporting files must be selected as
well. The Perl script update-alternatives provides a way of
ensuring that all the files associated with a specified package are selected as
a system default.
For example, to check what executables provide `x-window-manager', run:
update-alternatives --display x-window-manager
If you want to change it, run:
update-alternatives --config x-window-manager
And follow the instructions on the screen (basically, press the number next to
the entry you'd like better).
If a package doesn't register itself as a window manager for some reason (file
a bug if it's in error), or if you use a window manager from /usr/local
directory, the selections on screen won't contain your preferred entry. You
can update the link through command line options, like this:
The first argument to `--install' option is the symlink that points to
/etc/alternatives/NAME, where NAME is the second argument. The third argument
is the program to which /etc/alternatives/NAME should point to, and the fourth
argument is the priority (larger value means the alternative will more probably
get picked automatically).