postinst is in sssd-ad-common 1.16.1-1ubuntu1.
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 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28  | #!/bin/sh
set -e
case "$1" in
    configure)
        if dpkg --compare-versions "$2" lt-nl "1.16.0-4"; then
            if [ -x "/usr/bin/deb-systemd-helper" ]; then
                deb-systemd-helper purge sssd-pac.service >/dev/null
                deb-systemd-helper unmask sssd-pac.service >/dev/null
                deb-systemd-helper purge sssd-pac.socket >/dev/null
                deb-systemd-helper unmask sssd-pac.socket >/dev/null
            fi
        fi
    ;;
    abort-upgrade|abort-remove|abort-deconfigure)
    ;;
    *)
        echo "postinst called with unknown argument \`$1'" >&2
        exit 1
    ;;
esac
exit 0
 |