postinst is in bsdutils 1:2.20.1-5.1ubuntu20.
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 | #!/bin/sh -e
if [ -L /usr/doc/bsdutils ] ; then
rm -f /usr/doc/bsdutils
fi
|