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Install the libpaper1 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).
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 change the file permissions on the device.
The kbd and console-tools packages support this, edit
/etc/kbd/config or /etc/console-tools/config files.
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.
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 runs all of the scripts in /etc/rcS.d/ by sourcing or forking subprocess depending on their file extension to perform initialization such as to check and to mount file systems, to load modules, to start the network services, to set the clock, and to perform other initialization. Then, for compatibility, it runs the files (except those with a `.'in the filename) in /etc/rc.boot/ too. 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. (BTW,
Debian supplies invoke-rc.d as a wrapper for invoking the scripts
in /etc/init.d/.)
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.
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.
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).
Execute the command:
dpkg-scanpackages BIN_DIR OVERRIDE_FILE [PATHPREFIX] > my_Packages
where:
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.
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:
update-alternatives --install /usr/bin/x-window-manager \
x-window-manager /usr/local/bin/wmaker-cvs 50
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).
To remove an alternative you added, simply run:
update-alternatives --remove x-window-manager /usr/local/bin/wmaker-cvs
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The Debian GNU/Linux FAQ
version 3.1.5, 17 January 2007