Chapter 3. Binary packages

16

that other packages are de installed. (In this case, it may be appropriate to specify a conflict

against earlier versions of something that previously did not use

update alternatives

;

this is an exception to the usual rule that versioned conflicts should be avoided.)

3.10.1 Prompting in maintainer scripts

Package maintainer scripts may prompt the user if necessary. Prompting should be done by

communicating through a program, such as

debconf

, which conforms to the Debian Config 

uration management specification, version 2 or higher. Prompting the user by other means,

such as by hand

3

, is now deprecated.

The

Debian

Configuration

management

specification

is

included

in

the

debconf_specification

files in the

debian policy

package. It is also available from

the Debian web mirrors at

/doc/packaging manuals/debconf_specification.html

(

http://www.debian.org/doc/packaging manuals/debconf_specification.

html

)

.

Packages which use the Debian Configuration management specification may contain an addi 

tional

config

script and a

templates

file in their control archive

4

. The

config

script might

be run before the

preinst

script, and before the package is unpacked or any of its dependen 

cies or pre dependencies are satisfied. Therefore it must work using only the tools present in

essential packages.

5

Packages should try to minimize the amount of prompting they need to do, and they should

ensure that the user will only ever be asked each question once. This means that packages

should try to use appropriate shared configuration files (such as

/etc/papersize

and

/etc

/news/server

), and shared

debconf

variables rather than each prompting for their own list

of required pieces of information.

It also means that an upgrade should not ask the same questions again, unless the user has

used

dpkg   purge

to remove the package's configuration. The answers to configuration

questions should be stored in an appropriate place in

/etc

so that the user can modify them,

and how this has been done should be documented.

If a package has a vitally important piece of information to pass to the user (such as  don't

run me as I am, you must edit the following configuration files first or you risk your system

emitting badly formatted messages ), it should display this in the

config

or

postinst

script

and prompt the user to hit return to acknowledge the message. Copyright messages do not

count as vitally important (they belong in

/usr/share/doc/

package

/copyright

); neither

do instructions on how to use a program (these should be in on line documentation, where all

the users can see them).

Any necessary prompting should almost always be confined to the

config

or

postinst

script. If it is done in the

postinst

, it should be protected with a conditional so that unnec 

3

From the Jargon file: by hand 2. By extension, writing code which does something in an explicit or low level

way for which a presupplied library (debconf, in this instance) routine ought to have been available.

4

The control.tar.gz inside the .deb. See

deb(5)

.

5

Debconf

or another tool that implements the Debian Configuration management specification will also be

installed, and any versioned dependencies on it will be satisfied before preconfiguration begins.