What does the -f option do?

[pfofi]

I was wondering what the -f option does in mergerfs -f. It is only mentioned as part of the systemd mount example and not explained further.

I've noticed mergerfs won't stay alive if I start it via systemd without this option. Does it stand for 'foreground', so that mergerfs won't detach itself from the invoking process?

[trapexit]

Run mergerfs --help and it will explain it.

Yes, it is libfuse's standard "run in foreground" argument. By default it daemonizes.