Writing a simple systemd script

cd /usr/lib/systemd/system/

edit a file named simple.service with following contents:

===========================

[Unit]
Description=Simple Service
After=network.target

[Service]
Type=simple
ExecStart=/usr/bin/test
Restart=on-abort

[Install]
WantedBy=multi-user.target

===========================

Here, /usr/bin/test is the example program.

Now, check the status by default

$ systemctl status simple

● simple.service - Simple Service
   Loaded: loaded (/usr/lib/systemd/system/simple.service; disabled; vendor preset: disabled)
   Active: inactive (dead)

Start the service

$ sudo systemctl start simple

Now, check the status:

$ sudo systemctl status simple

output :

● simple.service - Simple Service
   Loaded: loaded (/usr/lib/systemd/system/simple.service; disabled; vendor preset: disabled)
   Active: active (running) since
 Main PID: 23791 (test)
   CGroup: /system.slice/simple.service
           └─23791 /usr/bin/test

systemd[1]: Started Simple Service.
systemd[1]: Starting Simple Service...

To stop the service:

$ sudo systemctl stop simple

To enable the service by default

sudo systemctl enable simple

Created symlink from /etc/systemd/system/multi-user.target.wants/simple.service to /usr/lib/systemd/system/simple.service.

$ ls -l /etc/systemd/system/multi-user.target.wants/simple.service

lrwxrwxrwx 1 root root  /etc/systemd/system/multi-user.target.wants/simple.service -> /usr/lib/systemd/system/simple.service

To get more idea about different keywords used in systemd script, refer man 5 systemd.service

For example in the above one following keywords are used:

ExecStart = command executed when service is started.

After = after the specific service started.

Restart= when to restart the service.

WantedBy= which run level this is required.