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Chapter 6

Package maintainer scripts and

installation procedure

6.1 Introduction to package maintainer scripts

It is possible to supply scripts as part of a package which the package management system will

run for you when your package is installed, upgraded or removed.

These scripts are the files

preinst

,

postinst

,

prerm

and

postrm

in the control area of the

package. They must be proper executable files; if they are scripts (which is recommended),

they must start with the usual

#!

convention. They should be readable and executable by

anyone, and not world writable.

The package management system looks at the exit status from these scripts. It is important that

they exit with a non zero status if there is an error, so that the package management system

can stop its processing. For shell scripts this means that you almost always need to use

set  e

(this is usually true when writing shell scripts, in fact). It is also important, of course, that they

don't exit with a non zero status if everything went well.

When a package is upgraded a combination of the scripts from the old and new packages is

called during the upgrade procedure. If your scripts are going to be at all complicated you

need to be aware of this, and may need to check the arguments to your scripts.

Broadly speaking the

preinst

is called before (a particular version of) a package is installed,

and the

postinst

afterwards; the

prerm

before (a version of) a package is removed and the

postrm

afterwards.

Programs called from maintainer scripts should not normally have a path prepended to them.

Before installation is started, the package management system checks to see if the programs

ldconfig

,

start stop daemon

,

install info

, and

update rc.d

can be found via the

PATH

environment variable. Those programs, and any other program that one would expect

to be on the

PATH

, should thus be invoked without an absolute pathname. Maintainer scripts

should also not reset the

PATH

, though they might choose to modify it by prepending or ap 

pending package specific directories. These considerations really apply to all shell scripts.