Within my systems
/run directory I have a bunch of files that have
*.pid extensions and store the process id of running daemons, i.e.
% ls -1 /run/*.pid acpid.pid crond.pid dhclient-wlp2s0.pid irqbalance.pid lightdm.pid nginx.pid rsyslogd.pid
And I have generally noticed this is something many other daemons do and that daemon management scripts in
/etc/init.d/* will read in the pid from the last running instance and reuse that on starting a new instance.
Why? why not just start the daemon and give it a new pid?
Are there other programs e.g. rsyslog, that are expecting that daemon to have that identifier and would be confused if a different program was using that pid?