id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
796	nginx.pid is removed during reload if pid path is changed in nginx.conf but points to the same file through a symlink	pdecat@…		"On recent debian systems and derivatives like Ubuntu, /var/run is a symlink to /run:
{{{
# ls -l /var/run                                                                                                                                                                                               
lrwxrwxrwx 1 root root 4 Jan 21  2015 /var/run -> /run
}}}

On such systems, if the path to the pid file is changed from /var/run/nginx.pid to /run/nginx.pid in nginx.conf, effectively pointing to the same file on the filesystem, then when the configuration is reloaded the new /run/nginx.pid file is created then destroyed when the old /var/run/nginx.pid is unlinked.

Following are the steps to reproduce this issue.

At first, the nginx service is running normally:
{{{
# grep nginx.pid /etc/nginx/nginx.conf 
pid /var/run/nginx.pid;
# cat /var/run/nginx.pid                                                                                                                                                                                       
1129
# ps -ef|grep nginx                                                                                                                                                                                            
root      1129     1  0 Sep21 ?        00:00:00 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
www-data  4290  1129  0 07:49 ?        00:00:00 nginx: worker process                           
www-data  4291  1129  0 07:49 ?        00:00:00 nginx: worker process                           
www-data  4292  1129  0 07:49 ?        00:00:00 nginx: worker process                           
www-data  4293  1129  0 07:49 ?        00:00:00 nginx: worker process                           
}}}

Simply reloading the configuration works fine:
{{{
# kill -HUP 1129                                                                                                                                                                                               
# ps -ef|grep nginx
root      1129     1  0 Sep21 ?        00:00:00 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
www-data  5171  1129  0 07:50 ?        00:00:00 nginx: worker process                           
www-data  5172  1129  0 07:50 ?        00:00:00 nginx: worker process                           
www-data  5173  1129  0 07:50 ?        00:00:00 nginx: worker process                           
www-data  5174  1129  0 07:50 ?        00:00:00 nginx: worker process                           
# cat /var/run/nginx.pid                                                                                                                                                                                       
1129
}}}

Changing the pid path from /var/run/nginx.pid to /run/nginx.pid then reloading the configuration exhibits the issue:
{{{ 
# sed -i 's/pid \/var\/run\/nginx.pid/pid \/run\/nginx.pid/' /etc/nginx/nginx.conf
# grep nginx.pid /etc/nginx/nginx.conf 
pid /run/nginx.pid;
# kill -HUP 1129
# ps -ef|grep nginx
root      1129     1  0 Sep21 ?        00:00:00 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
www-data  5950  1129  0 07:51 ?        00:00:00 nginx: worker process                           
www-data  5951  1129  0 07:51 ?        00:00:00 nginx: worker process                           
www-data  5952  1129  0 07:51 ?        00:00:00 nginx: worker process                           
www-data  5953  1129  0 07:51 ?        00:00:00 nginx: worker process                           
# cat /var/run/nginx.pid 
cat: /var/run/nginx.pid: No such file or directory
}}}

Using strace, this behaviour is explained because the previous path is unlinked after the new file is created:
{{{
    open(""/var/run/nginx.pid"", O_RDWR|O_CREAT|O_TRUNC, 0644) = 7
    pwrite(7, ""1129\n"", 5, 0)               = 5
    close(7)                                = 0
    unlink(""/run/nginx.pid"")                = 0
}}}

Issue first encountered on Debian Wheezy with nginx 1.6.2 from backports, then reproduced on Ubuntu with nginx 1.9.3."	defect	closed	minor		nginx-core	1.9.x	wontfix			Linux patrickxps 4.2.0-10-generic #12-Ubuntu SMP Tue Sep 15 19:43:01 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux	"nginx version: nginx/1.9.3 (Ubuntu)
built with OpenSSL 1.0.2d 9 Jul 2015
TLS SNI support enabled
configure arguments: --with-cc-opt='-g -O2 -fPIE -fstack-protector-strong -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2' --with-ld-opt='-Wl,-Bsymbolic-functions -fPIE -pie -Wl,-z,relro -Wl,-z,now' --prefix=/usr/share/nginx --conf-path=/etc/nginx/nginx.conf --http-log-path=/var/log/nginx/access.log --error-log-path=/var/log/nginx/error.log --lock-path=/var/lock/nginx.lock --pid-path=/run/nginx.pid --http-client-body-temp-path=/var/lib/nginx/body --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-proxy-temp-path=/var/lib/nginx/proxy --http-scgi-temp-path=/var/lib/nginx/scgi --http-uwsgi-temp-path=/var/lib/nginx/uwsgi --with-debug --with-pcre-jit --with-ipv6 --with-http_ssl_module --with-http_stub_status_module --with-http_realip_module --with-http_auth_request_module --with-http_addition_module --with-http_dav_module --with-http_geoip_module --with-http_gzip_static_module --with-http_image_filter_module --with-http_spdy_module --with-http_sub_module --with-http_xslt_module --with-mail --with-mail_ssl_module"