Cron – How to keep cron from stampeding

Cron can run many scripts at the same time. In fact, in Debian there are entire directories of cron scripts (ie. /etc/cron.daily /etc/cron.hourly) that execute at the same time.

If the script executes properly at a different time, why don't you try changing the time of the root cron job to determine whether the problem is with the actual timing, or a conflict between the scripts.

I also agree with turning off the redirect to /dev/null until you have everything working correctly.

a better way is to use flock instead of a pidfile. check the manpage: flock(1). The advantage is that no matter how a process finishes/dies, the lock is gone with it.