prerm is in shorewall6-lite 5.1.12.2-1.
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 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | #!/bin/sh -e
case "$1" in
    # do not stop the firewall during an upgrade
    remove)
        if [ -d "/run/systemd/system" ] && [ -f "/lib/systemd/system/shorewall6-lite.service" ]
        then
            deb-systemd-invoke stop shorewall6-lite.service
        elif [ -f "/etc/init.d/shorewall6-lite" ]
        then
            if [ -x "/usr/sbin/invoke-rc.d" ]
            then
                invoke-rc.d shorewall6-lite stop
            else
                /etc/init.d/shorewall6-lite stop
            fi
        fi
        ;;
    upgrade|deconfigure|failed-upgrade)
        ;;
    *)
        echo "prerem called with unknown argument \`$1\'" >&2
        exit 1
        ;;
esac
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