postinst is in powermanagement-interface 0.3.20.
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 | #!/bin/sh
case "$1" in
 configure)
        ucf /usr/share/pmi/defaults /etc/default/pmi
        ;;
 *)
        ;;
esac
 |