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Some remarks
  • Your lockfile's path will be relative to your current working directory. I'd suggest using an absolute path to avoid miscommunications.
  • Your sleep is called without argument, which means it'll sleep forever.
  • Are you sure that a parallel instance should exit? Without LOCK_NB it would wait till the lock is free.
  • You are not using parens for your arguments for flock(), precedence issues with | would make me nervous here. I'd need to look it up...
    it should work in this case tho.
Regarding debugging

You shouldn't rely on ps for debugging, append with >> to (another) absolute_path/logfile when your script is

  • started,
  • exiting,
  • working,
  • stopped,
including process ID and timestamp.

Please come back if you can really reproduce a problem.

Maybe of help:

File lock demo

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

In reply to Re: singleton lock not reliable by LanX
in thread singleton lock not reliable by pidloop

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