NetworkManager dispatcher script to start/stop a Systemd unit when a connection's status changes.

nm-systemd-dispatcher.sh

#!/bin/bash
# nm-systemd-dispatcher.sh
# Starts/stops a Systemd unit when a connection's status changes to up/down.
#
# Install this script to `/etc/NetworkManager/dispatcher.d/60-systemd.sh` and
# add the following section to your NetworkManager connection config in
# `/etc/NetworkManager/system-connections/*.nmconnection`:
#     [user]
#     systemd.unit=myservice.service
#
# Copyright (C) 2025 Daniel Rudolf (<https://www.daniel-rudolf.de>)
# License: The MIT License <http://opensource.org/licenses/MIT>
#
# SPDX-License-Identifier: MIT

print_usage() {
    echo "Usage:"
    echo "  ${BASH_SOURCE[0]} <interface> <action>"
}

[ $# -ge 2 ] || { print_usage >&2; exit 1; }

INTERFACE="$1"
ACTION="$2"

[ -n "$INTERFACE" ] || exit 0
[ "$ACTION" == "up" ] || [ "$ACTION" == "down" ] || exit 0
[ -n "${CONNECTION_USER_SYSTEMD__UNIT:-}" ] || exit 0

case "$ACTION" in
    "up")
        systemctl start "$CONNECTION_USER_SYSTEMD__UNIT"
        ;;

    "down")
        systemctl stop "$CONNECTION_USER_SYSTEMD__UNIT"
        ;;
esac