Oh great Monks, I am having an issue ensuring only one instance of my script runs at a time. Any help appreciated. This is a snippet version showing my technique: 
use strict;
use warnings;
use Fcntl ':flock';

# only one of us
open my $ME, '<', $0 or die "Couldn't open self: $!";
flock $ME, LOCK_EX | LOCK_NB or exit;

sleep;

[download]
This program is run every minute from a crontab. Doing a ps I expect to see exactly one instance. However, after a random period ranging from minutes to months I find two instances are running. I don't think it's an OS issue because I am seeing this on three different systems: centos 6 linux, macOS 11.4 and FreeBSD 12.2-RELEASE. So I'm actually hoping there is something wrong with this technique so I can fix it or there is a better way. Thanks for your time and wisdom.

In reply to singleton lock not reliable by pidloop

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