https://mailman.nginx.org/pipermail/nginx-ru/2010-May/034153.html
nginx & apache lockf
nginxapache
https://manpages.ubuntu.com/manpages/focal/man3/lockf.3.html
Ubuntu Manpage: lockf - apply, test or remove a POSIX lock on an open file
apply, test or remove a POSIX lock on an open file