Comment 23 for bug 1581864

I've developed and tested a different approach. More invasive and probably not something upstream will like the look of!

The approach is to have ngx_daemon() not do the parent process exit() after fork() but to return the child PID. The parent process detects that (a value > 0), sets ngx_pid = child_pid, calls ngx_crate_pidfile(), then does the exit().

I tested with extensive log messages to trace behaviour and confirmed it works.

Jun 01 03:01:51 u1910 systemd[1]: Starting A high performance web server and a reverse proxy server...
Jun 01 03:01:51 u1910 nginx[27728]: nginx: Initialise child_pid=-3
Jun 01 03:01:51 u1910 nginx[27728]: nginx: ngx_daemon() in PID 27728 returned 27729
Jun 01 03:01:51 u1910 nginx[27728]: nginx: Process PID 27728 calling ngx_create_pidfile() with ngx_pid=27729
Jun 01 03:01:51 u1910 nginx[27728]: nginx: Process PID 27728 exiting
Jun 01 03:01:51 u1910 nginx[27728]: nginx: ngx_daemon() in PID 27729 returned 0
Jun 01 03:01:51 u1910 nginx[27728]: nginx: This should be child process PID 27729, parent PID 27728
Jun 01 03:01:51 u1910 systemd[1]: Started A high performance web server and a reverse proxy server.