Linux scripts to run at startup

How to run script on startup using systemd in Linux

In this article I will share a sample systemd unit file which you can use to run script at startup with systemd without using crontab in RHEL/CentOS 7/8 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

There can be various scenarios when you expect a script or command to be called at startup such as

• Execute a script after waiting for N minutes of startup
• Execute a script after all the systemd services are loaded
• Execute a script immediately after login prompt appears
• Execute a script just before the login prompt appears

In this article I will cover below two topics as they are almost similar

• Run script at startup with systemd after network is reachable
• Execute script at starup after all the systemd services are loaded

I will be using CentOS/RHEL 7/8 Linux node to verify the steps from this article to run script with systemd right before login prompt.

Step 1: Overview on systemd

I hope you are already familiar with below topics

Step 2: Create Sample Script

Now to run script at startup with systemd firstly we need a script or command. For the sake of this article I have create a dummy shell script /tmp/startup_script.sh which we will use for testing this article.

[root@centos-8 ~]# cat /tmp/startup_script.sh #!/bin/bash SCRIPT_NAME=$(basename -- "$0") z=0 for i in ; do sleep 1m ((z++)) wall $SCRIPT_NAME: finished minute $ done wall $SCRIPT_NAME: COMPLETELY FINISHED

This script will continue to run for 5 minutes and will print an echo statement on the screen every minute as a broadcast message using wall command for all Linux users on the respective node. And at the end of 5th minute it will print a completed broadcast. With this we can also make sure that the script is not killed by systemd if it continues to run for 5 minutes .

Provide executable permission to the script

[root@centos-8 ~]# chmod u+x /tmp/startup_script.sh

Create a new systemd service unit file with following content:

[root@centos-8 ~]# cat /etc/systemd/system/run-at-startup.service [Unit] Description=Run script at startup after network becomes reachable [Service] Type=simple RemainAfterExit=yes ExecStart=/tmp/startup_script.sh TimeoutStartSec=0 [Install] WantedBy=default.target

Next to activate the changes, execute following command:

Enable the service to make sure this is called automatically after reboot

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

Step 3: Create systemd unit file for different scenario

Step 3.1: Run script at startup with systemd after network becomes reachable

In this scenario we will execute our script as soon as the network becomes reachable i.e. when network.target starts running during bootup stage by using After=network.target . The unit file should be located in either /usr/lib/systemd/system or /etc/systemd/system . I will place this under /etc/systemd/system as this is is used to place custom unit file.

[root@centos-8 ~]# cat /etc/systemd/system/run-at-startup.service [Unit] Description=Run script at startup after network becomes reachable After=network.target [Service] Type=simple RemainAfterExit=yes ExecStart=/tmp/startup_script.sh TimeoutStartSec=0 [Install] WantedBy=default.target

Step 3.2: Run script at startup with systemd after all systemd services are loaded

Now in this senario we must make sure all the systemd services for the respective target has loaded before starting the script. So to run script at startup with systemd after all systemd services are loaded we must defined our After= directive accordingly. Since the default.target will vary based on environment so rather than specifying specific target name we will use After=default.target so systemd will decide on it’s own the default.target and will call the script at startup in Linux.

[root@centos-8 ~]# cat /etc/systemd/system/run-at-startup.service [Unit] Description=Run script at startup after all systemd services are loaded After=default.target [Service] Type=simple RemainAfterExit=yes ExecStart=/tmp/startup_script.sh TimeoutStartSec=0 [Install] WantedBy=default.target

Step 3.3: Run script at startup with systemd after login prompt appears

Now in this scenario also we will only play around After= directive of the unit file. Now since the requirement is to run script at startup with systemd after login prompt appears then we will use After=getty.target

[root@centos-8 ~]# cat /etc/systemd/system/run-at-startup.service [Unit] Description=Run script at startup after all systemd services are loaded After=getty.target [Service] Type=simple RemainAfterExit=yes ExecStart=/tmp/startup_script.sh TimeoutStartSec=0 [Install] WantedBy=default.target

You can also create your own man page with a list of instructions for a script or a custom tool which you have created. In real time production environment it is always recommended to also create and release a man page for every script or tool we develop.

After= If the script needs any other system facilities (networking, etc), modify the [Unit] section to include appropriate After=, Wants=, or Requires= directives, as described in: man systemd.unit Type= Switch Type=simple for Type=idle in the [Service] section to delay execution of the script until all other jobs are dispatched (see man systemd.service for even more choices -- e.g., Type=oneshot can be useful in concert with other services). 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.

Here if you observe we have defined After=network.target to make sure the script

Refresh the systemd configuration files and enable the service

[root@centos-8 ~]# systemctl daemon-reload [root@centos-8 ~]# systemctl enable run-at-startup.service

Step 4: Verify the systemd unit file configuration

Now our configuration is in place to run script at startup in CentOS/RHEL 7/8 Linux.

You can also use systemctl list-jobs within the script to monitor the list of active jobs when the script was executed at startup.

Now post reboot of the Linux node we can see that our startup_script.sh is running in the background

[root@centos-8 ~]# ps -ef | grep startup root 805 1 0 11:38 ? 00:00:00 /bin/bash /tmp/startup_script.sh root 1198 1147 0 11:39 pts/0 00:00:00 grep --color=auto startup

Also in some time we start getting the broadcast messages from root user.

Broadcast message from root@centos-8.example.com (somewhere) (Thu Jan 16 11:39: startup_script.sh: finished minute 1 Broadcast message from root@centos-8.example.com (somewhere) (Thu Jan 16 11:40: startup_script.sh: finished minute 2 Broadcast message from root@centos-8.example.com (somewhere) (Thu Jan 16 11:41: startup_script.sh: finished minute 3 Broadcast message from root@centos-8.example.com (somewhere) (Thu Jan 16 11:42: startup_script.sh: finished minute 4 Broadcast message from root@centos-8.example.com (somewhere) (Thu Jan 16 11:43: startup_script.sh: finished minute 5 Broadcast message from root@centos-8.example.com (somewhere) (Thu Jan 16 11:43: startup_script.sh: COMPLETELY FINISHED

I have verified the script for both scenarios to run script at startup with systemd (witout crontab) in Linux but I am not putting output from both scenarios as the output is same in both case.

After boot, use systemd-analyze plot > file.svg to generate an image of the boot process for inspection. You can use any browser to view this file.svg and verify the boot process. There could be one or two short-lived services starting after run-at-startup.service . If that’s a problem, modify /etc/systemd/system/run-at-startup.service to set Type=idle

Lastly I hope the steps from the article to run script at startup with systemd without using crontab in CentOS/RHEL 7/8 Linux was helpful. So, let me know your suggestions and feedback using the comment section.

Related Searches: How to execute script at startup as soon as network is reacable in Linux. How to call a script or execute command at Linux startup once the login prompt is visible in Linux. How to execute script with systemd at startup once all the systemd services are loaded in RHEL/CentOS 7/8 Linux with examples. How to run script at startup with crontab and cron job. how to add startup scripts in redhat linux 7. run script on startup.

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8 thoughts on “How to run script on startup using systemd in Linux”

how would one write a SINGLE service file to run before shutdown, reboot AND also AFTER the network is up on startup? Or cannot this be done for both in a single file?
thanks
rich Reply

Any normal systemd service is expected to run at shutdown if ExecStop is found, similarly ExecStart is required to start a service during reboot and if you want it to happen after network then you can use After=network.target Although to run a service before shutdown and cover other scenarios, you can go through different articles which I have published on similar topics. Reply

OK But can these BOTH be put into a single service file? Or does the shutdown part have to go in one .service file and the startup in a separate .service file?
thanks
rich Reply

I don’t see any challenge in having a single service file. Please give it a try and let me know your results. Reply

[root@galaxy ~]# systemctl enable run-at-startup.service Failed to enable unit: Unit file run-at-startup.service does not exist.

you can check step 3.1 where I have provided the content of the systemd service unit file. You need to create this file /etc/systemd/system/run-at-startup.service
followed by systemctl daemon-reload Reply

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