Systemd setup

Whether that's good or bad, we're using systemd to manage "services", eg. running a website / web-app through some standard commands.

What this allows is to:

• run a specific program,
• check its status,
• restart it at will,
• tell systemd to start it automatically if we reboot the server,
• tell systemd to restart it automatically if the program crashes for some reasons,
• etc

List services

You can run this command to list all services managed by systemd:

systemctl list-units --type=service

This shows everything, and not only the services added by a specific user. As of now (as far as I know, which is little), we're not creating services under a specific user but under root (?), so there might be way to better filter out this list.

Add a service

To add a new service, follow these steps:

• create a new file under /etc/system/systemd: sudo touch /etc/system/systemd/<service-name>.service
• add the following as a starting point:

• [Unit]
  Description=<service-name>
  After=network.target
  
  [Service]
  Type=simple
  Restart=always
  RestartSec=1
  User=<user you want the web-app to run under>
  
  WorkingDirectory=<path/to/web-app/>
  ExecStart=<command to use to run the web-app>
  
  [Install]
  WantedBy=multi-user.target
  

  This is a very simplified example, please lookup for more detailed references in case you have something more complex.

As you can see in the service example above, we're telling systemd:

• Description: what's the name of the service
• After: when systemd should start the program (eg after the OS network is up and running)
• Type, Restart, User: hopefully, self-explanatory
• WorkingDirectory: tells systemd we want to run our ExecStart command from a specific directory
• WantedBy: I still don't understand what's this exactly, it seems necessary to let systemd know you want this service available

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After you created a new service file (or after you updated an existing one), you want to run this command to "refresh" systemd, so that it can see your new service:

sudo systemctl daemon-reload

Afterwards:

• enable the service (to make it start at system boot / reboot): sudo systemctl enable <service-name>.service

• start the service: sudo systemctl start <service-name>.service
• check its status: sudo systemctl status <service-name>.service
• restart it (in case you modified something in the web-app for instance): sudo systemctl restart <service-name>.service
• stop it: sudo systemctl stop <service-name>.service
• disable the service: sudo systemctl disable <service-name>.service

Debugging

While running sudo systemctl status <service-name>.service gives you an idea if the service is running fine or not, you don't get much more than that. Depending on your web-app setup (for instance), you might have setup a logging system.

In that case, you can also use the journalctl to access it, by doing:

sudo journalctl -e -u <service-name>.service

• -e: stands for "end", and it shows you the end of the logging file, eg the latest entries in the log
• -u: stands for "unit" (I believe), and lets you filter out which logs to display, by setting the service name you want to inspect