Creating the Systemd Unit

Systemd is a process manager can start, stop, and manage processes ("Units") on boot or shutdown of your machine! In this walkthrough, we'll be starting a long-running Node.js web server that lives in /var/www/.

To create a new Unit, we need to create a file in /etc/systemd/system/ (the default location most Linux distributions). This file should have the .service extension.

Let's create /etc/systemd/system/webserver.service:

# Since we're going to bind to a port on localhost, we need to wait for the
# network service to boot:
Description="My fancy web sever"

# Configure your long-running process:
# You'll want to adjust:
# * WorkingDirectory: change this to the directory your application is in
# * Environment: add or remove these options depending on your environment variable needs
# * ExecStart: this is the command that'll be run to start your application
WorkingDirectory=/var/www # set the cwd (current working directory)
ExecStart=npm start # start your webserver! e.g. `node server.js`
Restart=always # always restart the webserver if it crashes
RestartSec=3 # after a crash, wait 3 seconds before restarting the server

# Run this service anytime the system boots:

After you've created the file, update it to have the correct permissions (664):

chmod 664 /etc/systemd/system/webserver.service

Don't be intimidated by the file above! A lot of it is boilerplate. Read the comments placed in the above file to understand what each section is for!

You can learn more about the Unit or Service sections in the systemd documentation.

The Install section is used to configure when the service will start. Most commonly, you'll want The WantedBy value directly corresponds to different Linux runlevels:

runlevel WantedBy value Description
0 Run before the computer shuts down
1 Run when the system is in single-user mode
2-4 Run when the system is ready for login, but before networking is setup
5 Run when the display manager has started
6 Run before the computer reboots

Enabling the Systemd Unit

Now that the unit has been created, we need to reload the Systemd process. This will allow Systemd to recognize the new file.

Run the following command:

systemctl daemon-reload

Tip: You need to execute the above command to reload Systemd every time you edit your .service file(s).

Next, you'll need to enable the service. Running this command will create a symlink into your WantedBy target.

systemctl enable webserver

Finally, since your system is already booted, run the following command to start the service:

systemctl start webserver


Enabling (creating) or Disabling (deleting) your service

systemctl enable webserver # install a new service file
systemctl disable webserver # uninstall a service file

Starting, Restarting, or Stopping your service

systemctl start webserver
systemctl restart webserver
systemctl stop webserver

Checking the status of your service

systemctl status webserver