Using a Oneshot Systemd Service

15 minutes
  • 4 Learning Objectives

About this Hands-on Lab

Managing services with `systemd` is a skill that modern Linux system administrators require to enable or disable processes to run as a service on the system. Being able to troubleshoot systemd services is invaluable for correct system operation. In this activity, you will learn about managing systemd services by troubleshooting why a oneshot systemd service is failing. Once this activity is complete, you should be comfortable managing `systemd` services with `systemctl`.

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Use systemctl to check the status of target.service. Update the systemd oneshot service unit file named target.service.

Using systemctl check the status of the target.service.

systemctl status target.service
systemctl status -l target.service

Using the editor of your choice, update the /etc/systemd/system/target.service file to match the following contents.

[Unit] 
Description=Log when default target reached
After=cloud-final.service 

[Service] 
Type=oneshot        
RemainAfterExit=yes   
ExecStart=/bin/echo "--->  Reached default.target"
ExecStart=/bin/ls -l /etc/systemd/system/default.target 

[Install]  
# WantedBy is similar to runlevel
WantedBy=default.target 
Reload the `systemd` daemon for updated unit file to be available. Check to see if service will start.

Use the systemctl command to reload the systemd daemon, so the new unit file can be managed.

 systemctl daemon-reload

Use the systemctl command to start and check status of the target.service.

 systemctl start target.service
 systemctl status target.service
Enable the `target.service` and reboot system.

Using the systemctl command enable the target.service and reboot the system to verify operation of service at boot time.

 systemctl enable target.service
 reboot
Reconnect to system and check the status of the `target.service`.

First, you will need to use your lab credentials to reconnect to the system and access the root account. Then, use the systemctl command to view the status of the target.service. It should show that the target.service started correctly.

 sudo -i
 systemctl status target.service

Additional Resources

The lead System Administrator has implemented a service that runs once (oneshot) when the system reaches the default.target. This service is supposed to log when the system has reached the default.target, and list the link for the default.target, but this service is failing and we have been asked to troubleshoot the problem.

<br>Once the /etc/systemd/system/target.service has been corrected for the error inside it, we will have to reload the systemd daemon, and start the service to make sure it runs. Since this service is supposed to run at boot time, we will also make sure that the service is enabled, reboot the system, and check the status of the target.service to make sure it is starting properly.

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