man 2 flock lists only one error condition:

EWOULDBLOCK The file is locked and the LOCK_NB flag was selected.
As cfreak suggests, some process (maybe yours) already has the lock.

Seeing your reply to cfreak, yes, a cgi environment may well be running more than one instance of your script. If LOCK_NB is not set, one instance will wait until the other lets go.

Update: Calling flock as flock FH, $opts or warn $!; will tell you what error is set. I don't understand why LOCK_NB is necessary to you. For most purposes, the blocking form is preferred. The effect is to sleep until the file is available.

After Compline,
Zaxo

In reply to Re: Can flock occasionally fail on systems that support file locking? by Zaxo
in thread Can flock occasionally fail on systems that support file locking? by rzward

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