[systemd-devel] How to run forking daemon with systemd in correct way, without errors?

[Reindl Harald]

Am 23.11.2017 um 11:40 schrieb Gena Makhomed:
> On 23.11.2017 2:30, Reindl Harald wrote:
>> i know that all, httpd and postfix are typically forking services and 
>> are working fine without any PID file since 2011
> 
> # grep PIDFile /usr/lib/systemd/system/postfix.service
> PIDFile=/var/spool/postfix/pid/master.pid
> 
> httpd is not Type=forking service, it is Type=notify one.
> 
> # grep Type /usr/lib/systemd/system/httpd.service
> Type=notify

please don't tell me what my services are, it can be Type=notify only 
when mod_systemd is compiled in but there is not compelling reason to do so

[harry at rh:~]$ rpm -q httpd
httpd-2.4.29-2.0.fc26.20171030.rh.sandybridge.x86_64

>>> In any case, you are talking about something like workaround of the bug,
>>> but I am asking in systemd-devel mail list about root cause of this bug,
>>> how to fix this bug, and where bug is located - in nginx or in systemd?
>>
>> in nginx which obviously creates the pid file too late
> 
> Creating pid file from grandchild process is common UNIX pattern.
> 
> Thousands of daemons are working in this way. Rewrite them all?
> 
> May be fixing systemd is far more simple than fixing all daemons?

obviously the PID file don't exist when it is expected

http://thelinuxjedi.blogspot.co.at/2014/02/why-use-double-fork-to-daemonize.html
https://www.freedesktop.org/software/systemd/man/systemd.service.html

If set to forking, it is expected that the process configured with 
ExecStart= will call fork() as part of its start-up. The parent process 
is expected to exit when start-up is complete and all communication 
channels are set up. The child continues to run as the main daemon 
process. This is the behavior of traditional UNIX daemons. If this 
setting is used, it is recommended to also use the PIDFile= option, so 
that systemd can identify the main process of the daemon. systemd will 
proceed with starting follow-up units as soon as the parent process exits.