Motivated by the --daemon flag recently added: iperf3 should provide an option to write its PID to a file, where a (hypothetical) startup script would be able to find it for the purposes of checking its status, stopping or restarting it, etc.

Writing the PID file itself is easy, but it should be cleaned up on process exit, and there are multiple ways to exit the program.

This would be so useful for automation. Think of a use case where you have multiple servers of iperf running on different ports and you need to restart one of them. If we know the PID of the process that's running on the specific port where I need to restart I can kill that one only and then create a new one on that same port.

I have this issue right now and will have to think of another workaround.

Thanks!

Committed to mainline in 6e6093f9ce8b.

Give this a more definite target; it might be a candidate for a backport.

In any case, resolving as fixed.