Initiate bash script on shutdown, but not on reboot

Question

I'm setting up my Linux box (that is connected to a UPS) to gracefully shutdown my pfsense router prior to shutting down. I'm running Ubuntu 16.04, and using systemd to accomplish this. I have the systemd service configured, and it works. However, it's initiating the script on shutdown AND on reboot. This is no good since anytime I reboot my linux box, I'll be shutting down my router. How can I change my systemd service so that it only activates during shutdown?

My setup is as follows:

[Unit]
Description=PFSense Shutdown script
After=poweroff.target

[Service]
Type=oneshot
ExecStart=/bin/true
ExecStop=/path/to/script/pfsenseshutdown.sh
RemainAfterExit=yes


[Install]
WantedBy=multi-user.target

And, for reference, the pfsenseshutdown.sh script is fairly simple:

#!/bin/bash
ssh user@x.x.x.x -i "sudo /etc/rc.halt"

Any help would be greatly appreciated.

Answer 1

The following approach seems to run a script on shutdown only, and not on reboot. You can edit the systemd-poweroff.service file as follows:

sudo systemctl edit --full systemd-poweroff.service

In the [Service] section, you can then add an ExecStartPre line:

ExecStartPre=/path/to/script/pfsenseshutdown.sh

This way, the script will not be executed if you shutdown the system with halt however. To handle this case, you can add the same line to systemd-halt.service.

Note that in this approach the config file shown in the question is not used.

EDIT: a possible shortcoming in the previous approach, is that the script to be executed contains an ssh command, which may not work right before shutting down the system (systemd may already have stopped necessary network services). The approach below tries to avoid this.

For this solution, I created a pfsenseshutdown.service unit with the following contents

[Unit]
Description=PFSense Shutdown script
DefaultDedendencies=no

[Service]
Type=oneshot
ExecStart=/usr/bin/touch /dev/shm/shuttingdown

[Install]
WantedBy=systemd-halt.service systemd-poweroff.service

When starting the shutdown procedure, this file seems to cause the ExecStart line to be executed right away, causing the file /dev/shm/shuttingdown to exist (the /dev/shm directory is a memory file system, so it will be cleared after a reboot).

Now, to make sure that your script is executed before the network is completely de-initialized, I ran

systemctl edit --full networking.service

Originally, it contained the following ExecStop line on my ubuntu 16.04 virtual machine:

ExecStop=/sbin/ifdown -a --read-environment

This line was replaced by a version that first runs your script, in this example:

ExecStop=/path/to/script/pfsenseshutdown.sh && /sbin/ifdown -a --read-environment

The pfsenseshutdown.sh script, then tests if the file in /dev/shm exists, and performs the ssh command accordingly. I also added a small sleep command: systemd does many things in parallel, and this hopefully helps prevent the test from failing because the file does not exist yet.

#!/bin/bash

sleep 1

if [ -e /dev/shm/shuttingdown ] ; then

    # Your ssh command here

fi