postinst is in dmsetup 2:1.02.110-1ubuntu10.
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  | #!/bin/sh
set -e
case "$1" in
    configure)
        if [ -x /usr/sbin/update-initramfs ]; then
            update-initramfs -u
        fi
    ;;
esac
exit 0
 |