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9.4.5. Defining installation scripts

In addition to the section described previously for controlling the build of the package software, you can define more scripts in your RPM spec files. RPM supports a script run prior to installation, %pre, and a script run after installation, %post. The same concepts apply when a package is erased, or uninstalled. The %preun script is run just before the uninstall and the %postun script just after the uninstall.
Cross Reference
Chapter 10, Advanced RPM Packaging covers triggers, another form of script that gets run when packages are installed or removed.
Start your scripts with the RPM section marker for the given script, such as %pre for the pre-install script. Then, place the shell commands you want to run. For example, the following define %post, %preun and %postun scripts from the ypbind networking package:
/sbin/chkconfig --add ypbind
if [ "$1" = 0 ] ; then
/sbin/service ypbind stop > /dev/null 2>&1
/sbin/chkconfig --del ypbind
exit 0
if [ "$1" -ge 1 ]; then
/sbin/service ypbind condrestart > /dev/null 2>&1
exit 0
Few packages need to perform any work prior to installation, so the %pre script is rarely used.
In this example, the chkconfig command is called to update the runlevel information for system services after installation and prior to removal. This is an example where just installing the application, ypbind in this case, is not enough. Since this application acts as a system service, more work needs to be done to finish the installation with the %pre script or clean up the service on removal with the %preun script.
Do not try to write interactive scripts. Many users install RPMs automatically. In such cases, or if the user runs a graphical RPM tool, any information your scripts output will be lost. User input will not be available.
The rpm command will pass one argument to your scripts, shown as $1 in the previous example, which holds a count of the number of versions of the package that are installed. Table 10-3 lists the counts for specific cases.
Table 10-3 Install and uninstall script count values
Install the first time
2 or higher (depending on the number of versions installed)
Remove last version of package
The previous script example accesses the count using the shell variable $1.