How to run script with systemd right before shutdown in Linux

In this article I will share example and sample systemd unit service file to run script with systemd right before shutdown in CentOS/RHEL 7/8 Linux. Using this systemd unit file you can run either some command or script as a last service before shutdown in Linux.

Now ideally any systemd service gets called via ExecStop at shutdown stage and with ExecStart at boot up stage. But here our requirement is little different, we wish to run script with systemd right before shutdown stage. Now this can be a normal shutdown or reboot.

Step 1: Overview on systemd

If you are a beginner to systemd then I would recommend you to also readOverview on systemd and how it is different from legacy SysV scriptsbefore starting with this tutorial.

Step 2: Create Sample Script

Now to run script with systemd right before shutdown we need a script or command. For the sake of this article I will use a script from another article of mine /tmp/startup_script.sh. This script will run for 3 minutes in a loop to check and make sure the script is not killed due to shutdown. We want the script to run and halt the shutdown until completely executed

# cat /tmp/startup_script.sh
#!/bin/bash
z=0
for i in {1..3}; do
    sleep 1m
    ((z++))
    echo ""
done

Provide executable permission to the script

chmod u+x /tmp/startup_script.sh

Step 3: Create unit file to run script with systemd right before shutdown

Now as highlighted under step 1, I have already written another article with the steps to create a new systemd unit file. Here we will name our systemd unit file as run-before-shutdown.service under /etc/systemd/system. Below is the content of run-before-login-prompt.service

[root@centos-8 ~]# cat /etc/systemd/system/run-before-shutdown.service
[Unit]
Description=Run my custom task at shutdown
DefaultDependencies=no
Before=shutdown.target

[Service]
Type=oneshot
ExecStart=/tmp/startup_script.sh
TimeoutStartSec=0

[Install]
WantedBy=shutdown.target

Here the main task is done by Before=shutdown.target and TimeoutStartSec=0. For more details check man page of systemd.service

TimeoutStartSec=    When a service doesn't signal start-up completion within TimeoutStartSec, systemd considers the service failed; 
            for long-running shell scripts it is essential to modify TimeoutStartSec or disable the timeout logic altogether 
            as above, with TimeoutStartSec=0. See man systemd.service for more details.

Before=        If the script needs to be run before other services--for example, prior to starting sshd or console/graphical 
            logins ensure there is a Before=XYZ.service in the [Unit] section and a corresponding RequiredBy=XYZ.service 
            in the [Install] section.

Refresh the systemd configuration files

[root@centos-8 ~]# systemctl daemon-reload

Enable the script to automatically start at next boot

[root@centos-8 ~]# systemctl enable run-before-shutdown.service
Created symlink /etc/systemd/system/shutdown.target.wants/run-before-shutdown.service → /etc/systemd/system/run-before-shutdown.service.

Step 3: Verify the systemd unit file configuration

Now since we are done with the setting up of systemd. Let us verify our configuration.

reboot

We are using Oracle VirtualBox so post reboot we will check the console of our Virtual Machine

As expected we see that our systemd service is running and not allowing shutdown to complete.

Lastly I hope the steps from the article to run script with systemd right before shutdown on CentOS/RHEL 7/8 Linux was helpful. So, let me know your suggestions and feedback using the comment section.

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