id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
1897	Systemd is unable to read pidfile after nginx start-up due to a race-condition	turchanov@…		"Systemd unit nginx.service (packaged in your rpms but that same setup is used almost everywere):
{{{
...

[Service]
Type=forking
PIDFile=/var/run/nginx.pid
ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s TERM $MAINPID

...
}}}

The problem is that `$MAINPID` sometimes is empty, so that a ""reload"" or a ""stop"" operation won't work.
`$MAINPID` is populated from PIDFile (see `man systemd.service`) and here we have a race condition:
1. parent nginx process does fork and terminates, at this moment systemd tries to read PIDFile which is empty (because forked nginx child hasn't written pid file yet)
2. forked nginx child does write a pid value to PIDFile but that happens too late 

This bug is also present in Ubuntu bug-tracker (https://bugs.launchpad.net/ubuntu/+source/nginx/+bug/1581864).
There is a work-around - to insert a small delay:
{{{
ExecStartPost=/bin/sleep 0.1
}}}
it does alleviate the problem. The real solution suggested in  Ubuntu bug-tracker is to write pidfile in parent nginx process after fork but before exiting - this closes the race condition.

Will you, please, port suggested solution to the mainline codebase or work something along the lines to solve this problem?"	defect	closed	minor		other	1.14.x	wontfix			Linux n1 4.19.42-204.el7fc.x86_64 #1 SMP Tue May 14 21:31:24 +10 2019 x86_64 x86_64 x86_64 GNU/Linux	"nginx version: nginx/1.14.1
built by gcc 7.3.1 20180303 (Red Hat 7.3.1-5) (GCC) 
built with OpenSSL 1.0.2k-fips  26 Jan 2017
TLS SNI support enabled
configure arguments: --prefix=/opt/nginx-1.14.1 --pid-path=/var/run/nginx.pid --http-client-body-temp-path=/tmp/nginx-client_body_temp --http-proxy-temp-path=/tmp/nginx-proxy_temp --http-fastcgi-temp-path=/tmp/nginx-fastcgi_temp --http-uwsgi-temp-path=/tmp/nginx-uwsgi_temp --http-scgi-temp-path=/tmp/nginx-scgi_temp --with-pcre --with-pcre-jit --with-threads --with-http_ssl_module --with-http_v2_module --with-http_stub_status_module --with-http_gzip_static_module --with-http_gunzip_module --with-http_realip_module --with-stream --with-stream_ssl_module --with-http_geoip_module=dynamic
"