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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.
Some more articles on similar topic:
- How to execute a command or script with systemd at shutdown only and not at reboot in Linux
- How to execute a command or script with systemd right before login prompt appears on terminal in Linux
- How to execute a command or script at system startup using systemd without using cronjob in Linux
- How to execute a command or script after N minutes of boot up (system startup) with systemd in Linux
- How to halt system reboot or shutdown and read user input during boot up stage in Linux
- How to execute a command or script using systemd right before shutdown happens in Linux
- How to run a service as a specific user or group using systemd 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
I hope you are already familiar with below topics
- Overview on systemd and how it is different from legacy SysV scripts
- How to create a systemd unit file in Linux
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
[root@centos-8 ~]# 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.
[root@centos-8 ~]# 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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