postrm is in gcj-5-jre-headless 5.3.1-14ubuntu2.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | #! /bin/sh -e
case "$1" in
purge)
rm -f /var/lib/gcj-5/classmap.db
esac
exit 0
|