[systemd-devel] Antw: [EXT] [systemd‑devel] PIDFile creation logic

[Ulrich Windl]

>>> Kenneth Porter <shiva at sewingwitch.com> schrieb am 18.10.2021 um 21:43 in
Nachricht <95B112234248FF54AD014623@[192.168.1.16]>:
> I just installed the new‑to‑EPEL ndppd service and am seeing this in my
log:
> 
> Oct 17 21:10:08 saruman systemd: Can't open PID file 
> /var/run/ndppd/ndppd.pid (yet?) after start: No such file or directory
> 
> Examining the source, I see that the pidfile is created by the child 
> process, not the parent. I'm guessing that systemd is expecting the pidfile

> to exist when the parent exits? (I want to file the issue on the upstream 
> program and want to make sure I understand how this should work.)
> 
> Source in question. Note how daemonize() forks and exits and main() invokes

> daemonize and then creates the pidfile. I'm thinking that daemonize() 
> should create the pidfile before it invokes exit().
> 
> <https://github.com/DanielAdolfsson/ndppd/blob/master/src/ndppd.cc>

I had the same incompatibility problem in my own daemon, and the fix was like
this (still somewhat inefficient):
...
                        else if ( pid == 0 )
                        {
                                /* wait for parent to exit */
                                while ( getppid() != 1 )
                                        milli_sleep(5);
                                /* child continues */
...

Regards,
Ulrich