[systemd-devel] GuessMainPID=no required to make daemon reload work

[Kirill Elagin]

I've just tested the way I described it and everything worked perfectly.
Definitely the issue is this short period of time, I'm almost sure
(didn't check the source, though) that systemd re-reads pidfile
the moment the main process terminates.

What's wrong with writing the new pid from the old proccess before
releasing the lock?


--
Кирилл Елагин


On Mon, May 5, 2014 at 12:00 PM, Gerd v. Egidy <lists at egidy.de> wrote:

> Hi Кирилл,
>
> > OK, I've just re-read your message and it looks like all you need is add
> > `PIDFile` to your unit.
>
> This was the first thing I tried when writing the service file.
> Unfortunately it
> does not work, the service is declared dead and the new daemon is killed
> (unless I switch off killing, but then the state is still wrong and I can't
> stop the process in a sane way).
>
> > systemd will behave as expected: once your main process terminates it
> will
> > re-read PID
> > from this file (assuming that before dying your old process writes its
> > child's PID) and set it as MAINPID for your service.
>
> Hmm. Currently it is done like this: the old daemon releases the lock on
> the
> pidfile and terminates itself. The new daemon detects this and then writes
> it's
> own pid to the pidfile and locks it.
>
> So there is a short time where the old daemon is already dead and the new
> one
> hasn't written it's pid yet. Probably this is the problem. But I have to
> think
> about a way to get the locking stuff right as I can't easily transfer the
> lock
> over an exec.
>
> > But again, if your daemon is not writing a pidfile now, this way is not
> > “without changing the daemon itself first”.
>
> The current daemon already writes a pidfile. And to be more precise, it is
> not
> a problem to change the daemon, but I'd prefer not to introduce systemd-
> specific code or dependencies (like sd_notify) in the first step.
>
> Kind regards,
>
> Gerd
>
>
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