We removed tens of thousands of lines of code for fixes for those "simple" init scripts when migrating to systemd.
They are never "simple", there is always some fucking edge case, like for example we had Java apps writing its own PID few seconds after start. So any app that did start and immediately after status (like Pacemaker) threw errors.
Or how once in blue moon MySQL didn't start after reboot because it so happened that:
* the PID file from previous boot wasn't cleared
* some other app ran with same PID as it was in file
* Script did not care, script saw pid file existing and didn't start MySQL.
They are never "simple", there is always some fucking edge case, like for example we had Java apps writing its own PID few seconds after start. So any app that did start and immediately after status (like Pacemaker) threw errors.
Or how once in blue moon MySQL didn't start after reboot because it so happened that:
* the PID file from previous boot wasn't cleared * some other app ran with same PID as it was in file * Script did not care, script saw pid file existing and didn't start MySQL.
Both examples from pre-systemd CentOS