How to teach systemd to detect service process is already running

Times change and so do best practices.

The current best way to do this is to run systemctl edit myservice, which will create an override file for you or let you edit an existing one.

In normal installations this will create a directory /etc/systemd/system/myservice.service.d, and inside that directory create a file whose name ends in .conf (typically, override.conf), and in this file you can add to or override any part of the unit shipped by the distribution.

For instance, in a file /etc/systemd/system/myservice.service.d/myenv.conf:

[Service]
Environment="SECRET=pGNqduRFkB4K9C2vijOmUDa2kPtUhArN"
Environment="ANOTHER_SECRET=JP8YLOc2bsNlrGuD6LVTq7L36obpjzxd"

Also note that if the directory exists and is empty, your service will be disabled! If you don't intend to put something in the directory, ensure that it does not exist.

For reference, the old way was:

The recommended way to do this is to create a file /etc/sysconfig/myservice which contains your variables, and then load them with EnvironmentFile.

For complete details, see Fedora's documentation on how to write a systemd script.

If you need to run shell script only once, then just add ExecStartPre=/path/to/script and run your daemon with ExecStart=/path/to/daemon. The script will not run on restart, maybe this is not what you need.

If you need to run the script on reboots as well, then set Type=simple and run the daemon in foreground mode from shell script, so the script will not quit. But you still get that message and stop/restart actions are waiting 30 seconds before State 'stop-sigterm' timed out. Killing, very unpleasant. If you then add ExecStop=/bin/kill $MAINPID, the timeout problem goes away. Don't remove PIDFile. You will still see that message, but every action start/stop/restart/status work correctly. Maybe there is another better way to achieve the same. At least this works for me and the message may be safely ignored. When daemon quits, shell script will also quit, so systemd will know that.