spec文件中的 %pre %post %preun %postun

转载http://meinit.nl/rpm-spec-prepostpreunpostun-argument-values

RPM has 4 parts where (shell) scripts can be used:

• %pre - Executed before installation.
• %preun - Executed before un-installation.
• %post - Executed after installation.
• %postun - Executed after un-installation.

In all these parts or sections the variable "$1" can be checked to see what's being done:

• Initial installation
• Upgrade
• Un-installation

This table show the values of "$1" per section related to the action.

	%pre	%preun	%post	%postun
Initial installation	1	not applicable	1	not applicable
Upgrade	2	1	2	1
Un-installation	not applicable	0	not applicable	0

This can be used for example when registering new services:

%post
case "$1" in
  )
    # This is an initial install.
    chkconfig --add newservice
  ;;
  )
    # This is an upgrade.
    # First delete the registered service.
    chkconfig --del newservice
    # Then add the registered service. In case run levels changed in the init script, the service will be correctly re-added.
    chkconfig --add newservice
  ;;
esac

%preun
case "$1" in
  )
    # This is an un-installation.
    service newservice stop
    chkconfig --del newservice
  ;;
  )
    # This is an upgrade.
    # Do nothing.
    :
  ;;
esac

Good to know; this is the order for certain RPM actions:

install	upgrade	un-install
%pre ($1=1)	%pre ($1=2)	%preun ($1=0)
copy files	copy files	remove files
%post ($1=1)	%post ($1=2)	%postun ($1=0)
	%preun ($1=1) from old RPM.
	delete files only found in old package
	%postun ($1=1) from old RPM.

So when upgrading the exemplary package "software" from version 1 to version 2, this is the script (%post and %postun) order:

1. Run %pre from "software-2".
2. Place files from "software-2".
3. Run %post from "software-2".
4. Run %preun from "software-1".
5. Delete files unique to "software-1".
6. Run %postun from "software-1".

This means there are cases where "software-1" has incorrect scripts, and there is no way to upgrade. In that case the RPM can be uninstalled, which might execute different commands because $1 equals 0 (un-install) instead of 1 (upgrade).
When the RPM uninstall scripts fail, the only way to fix things is to manually execute the intended commands... RPM is not perfect, but it's pretty well thought through!