[systemd-devel] Antw: [EXT] Re: Child of daemon sending SIGCHLD to systemd

[Ulrich Windl]

>>> Ian Pilcher <arequipeno at gmail.com> schrieb am 02.07.2020 um 01:58 in
Nachricht
<rdj7ug$8st$1 at ciao.gmane.io>:
> On 7/1/20 3:47 AM, Mantas Mikulėnas wrote:
>> systemd doesn't explicitly reparent processes; the kernel just always 
>> reparents processes to pid 1 when the previous parent no longer exists. 
>> Overall, pid 1 is a legitimate recipient of SIGCHLD regardless of which 
>> init system is being used.
> 
> In this case, the parent definitely still exists.  As I mentioned in my
> previous note, just because I saw an SELinux AVC about the helper
> application sending SIGCHLD to and init_t process, that doesn't make it
> 100% certain that the signal was actually sent to systemd; it's possible
> that some other, related action is also included in the SELinux
> "sigchld" permission, possibly something that would be triggered if
> systemd's heuristics decided that the helper process was actually the
> "main PID" of the service.
> 
>> With Type=forking, systemd is able to read from whatever PIDFile= your 
>> daemon creates, if it creates any. This would also remove the need for 
>> GuessMainPID.
> 
> The daemon doesn't create  PID file, and I'm certainly not going to add
> that functionality now.  :-)

How does you daemon detect that it's running already? ;-)

> 
>> The ideal choice would be Type=notify, however, since it adds readiness 
>> notification on top of Type=simple. (With simple, other daemons wouldn't 
>> be able to properly order After=freecusd, but with Type=notify you only 
>> need to call sd_notify("READY=1") at the proper moment.)
> 
> Good thought.  This daemon doesn't provide services to anything else on
> the NAS.  It just monitors things, displays the status on the front-
> panel LCD display and LEDs, and controls the fan speed.  That being the
> case, I don't think that there's any real benefit to it in this case.
> 
> If that ever changes, though ...
> 
> -- 
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