deb-prerm - package pre-removal maintainer script
DEBIAN/prerm
A package can perform several pre-removal actions via maintainer scripts, by including an executable prerm file in its control archive (i.e. DEBIAN/prerm during package creation).
The script can be called in the following ways:
Before the package is removed.
Before an upgrade.
If the above upgrade fails. The new-version is passed only since dpkg 1.18.5.
Before package is deconfigured while dependency is replaced due to conflict.
Before the package is replaced due to conflict.