postinst is in pdns-backend-pipe 4.1.1-1.
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 | #!/bin/sh
set -e
dpkg-trigger pdns-server
exit 0
|