preinst is in lvm2 2.02.176-4.1ubuntu3.
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  | #!/bin/sh
set -e
case "$1" in
    upgrade)
        if dpkg --compare-versions "$2" lt 2.02.122-2; then
            if [ -x "/usr/bin/deb-systemd-helper" ]; then
                deb-systemd-helper purge lvm2-activation.service lvm2-activation-early.service >/dev/null
                deb-systemd-helper unmask lvm2-activation.service lvm2-activation-early.service >/dev/null
            fi
        fi
    ;;
esac
exit 0
 |