Set up a new systemd service

systemd is a modern init system and service manager for Linux, known for its efficient parallelization, robust dependency management, and powerful logging capabilities.
The need to add a new service to systemd can vary, whether you want to ensure a script restarts if it stops or you need to manage dependencies to guarantee the script’s prerequisites are available, systemd provides a straightforward solution for service management.

Here are the general steps for adding a new service to systemd:

1. Create the unit file:

   touch /etc/systemd/system/YOUR-SERVICE-NAME.service

2. Define the service with the necessary parameters, here is a basic example:

   [Unit]
   # Description of the service
   Description=My Custom Service
    
   # Ensure this service starts after the network is up
   After=network.target mysql.service
    
    
   [Service]
   # Command to execute when starting the service
   ExecStart=/path/to/your/script.sh
    
   # Restart the service if it stops
   Restart=always
    
   # Run the service as this user
   User=username
    
    
   [Install]
   # Start this service when the system reaches multi-user.target
   WantedBy=multi-user.target

   For additional information, I recommend visiting Red Hat’s documentation on systemd unit files.

3. Reload systemd:

   sudo systemctl daemon-reload

4. Enable and start your new service:

   sudo systemctl enable YOUR-SERVICE-NAME
   sudo systemctl start YOUR-SERVICE-NAME

   You can check the status of your script by using:

   systemcrtl status YOUR-SERVICE-NAME

POC:

Let’s say I have a script (/usr/local/bin/poc.sh) that should write “Hello” to a file (/var/check-service) every 5 minutes:

#!/bin/bash
 
# In seconds
timetowait=300
 
while true
do
    echo "`date` - Hello :)" >> /var/check-service
    sleep "$timetowait"
done

And I want to use it as a service.

For the sake of this example, we’ll call the service “poc”, so the unit file should be named poc.service:

noam@noam:~➤ touch /etc/systemd/system/poc.service

And the contents of it would be:

[Unit]
Description=Proof of concept
After=systemd-udevd.service systemd-timesyncd.service
 
[Service]
ExecStart=/usr/local/bin/poc.sh
Restart=always
User=noam
 
[Install]
WantedBy=default.target

Note that the “After” directive specifies that the script should only be loaded after both “systemd-udevd.service” and “systemd-timesyncd.service” have been loaded. This ensures that the script is executed after these services, considering its file writing and time-checking operations.

Then, we’ll reload systemd:

noam@noam:~➤ sudo systemctl daemon-reload

And enable and start the script:

noam@noam:~➤ sudo systemctl enable poc
Created symlink /etc/systemd/system/default.target.wants/poc.service → /etc/systemd/system/poc.service.
noam@noam:~➤ sudo systemctl start poc

Finally, we can check the status of the service:

noam@noam:~➤ sudo systemctl status poc
● poc.service - Proof of concept
Loaded: loaded (/etc/systemd/system/poc.service; enabled; vendor preset: enabled)
Active: active (running) since Sat 2024-05-18 22:29:02 IDT; 2s ago
Main PID: 1461092 (poc.sh)
Tasks: 2 (limit: 18721)
Memory: 548.0K
CPU: 3ms
CGroup: /system.slice/poc.service
├─1461092 /bin/bash /usr/local/bin/poc.sh
└─1461094 sleep 300
 
May 18 22:29:02 noam systemd[1]: Started Proof of concept.

And it seems like it works just fine, we can even check the /var/check-service file for changes: