Chapter 10. Customizing your installation of Debian GNU/Linux

57

  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 pack 

ages 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, oth 

ers 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 function 

ality, 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 pro 

gram 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, man 

ual 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 speci 

fied package are selected as a system default.

For example, to check what executables provide `x window manager', run:

update alternatives   display x window manager