Chapter 3. Binary packages

14

Sometimes, a package requires another package to be installed and configured before it can be

installed. In this case, you must specify a

Pre Depends

entry for the package.

You should not specify a

Pre Depends

entry for a package before this has been discussed on

the

debian devel

mailing list and a consensus about doing that has been reached.

The format of the package interrelationship control fields is described in `Declaring relation 

ships between packages' on page

45

.

3.6 Virtual packages

Sometimes, there are several packages which offer more or less the same functionality. In this

case, it's useful to define a virtual package whose name describes that common functionality.

(The virtual packages only exist logically, not physically; that's why they are called virtual.) The

packages with this particular function will then provide the virtual package. Thus, any other

package requiring that function can simply depend on the virtual package without having to

specify all possible packages individually.

All packages should use virtual package names where appropriate, and arrange to create new

ones if necessary. They should not use virtual package names (except privately, amongst a

cooperating group of packages) unless they have been agreed upon and appear in the list of

virtual package names. (See also `Virtual packages  

Provides

' on page

48

)

The latest version of the authoritative list of virtual package names can be found

in the

debian policy

package.

It is also available from the Debian web mir 

rors at

/doc/packaging manuals/virtual package names list.txt (

http://

www.debian.org/doc/packaging manuals/virtual package names list.txt

)

.

The procedure for updating the list is described in the preface to the list.

3.7 Base system

The

base system

is a minimum subset of the Debian GNU/Linux system that is installed

before everything else on a new system. Thus, only very few packages are allowed to go into

the

base

section to keep the required disk usage very small.

Most of these packages will have the priority value

required

or at least

important

, and

many of them will be tagged

essential

(see below).

3.8 Essential packages

Some packages are tagged

essential

for a system using the

Essential

control file field.

The format of the

Essential

control field is described in `

Essential

' on page

32

.