Edit Article: Systemd setup

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Whether that's good or bad, we're using <code>systemd</code> 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:<syntaxhighlight lang="bash"> systemctl list-units --type=service </syntaxhighlight>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 <code>/etc/system/systemd</code>: <code>sudo touch /etc/system/systemd/<service-name>.service</code> * add the following as a starting point: * <syntaxhighlight lang="bash"> [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 </syntaxhighlight>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: * <code>Description</code>: what's the name of the service * <code>After</code>: when systemd should start the program (eg after the OS network is up and running) * <code>Type</code>, <code>Restart</code>, <code>User</code>: hopefully, self-explanatory * <code>WorkingDirectory</code>: tells systemd we want to run our ExecStart command from a specific directory * <code>WantedBy</code>: I still don't understand what's this exactly, it seems necessary to let systemd know you want this service available 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:<syntaxhighlight lang="shell"> sudo systemctl daemon-reload </syntaxhighlight>Afterwards: * enable the service (to make it start at system boot / reboot): <code>sudo systemctl enable <service-name>.service</code> * start the service: <code>sudo systemctl start <service-name>.service</code> * check its status: <code>sudo systemctl status <service-name>.service</code> * restart it (in case you modified something in the web-app for instance): <code>sudo systemctl restart <service-name>.service</code> * stop it: <code>sudo systemctl stop <service-name>.service</code> * disable the service: <code>sudo systemctl disable <service-name>.service</code> === Debugging === While running <code>sudo systemctl status <service-name>.service</code> 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 <code>journalctl</code> to access it, by doing:<syntaxhighlight lang="shell"> sudo journalctl -e -u <service-name>.service </syntaxhighlight> * <code>-e</code>: stands for "end", and it shows you the end of the logging file, eg the latest entries in the log * <code>-u</code>: stands for "unit" (I believe), and lets you filter out which logs to display, by setting the service name you want to inspect [[Category:Infrastructure]]

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