How to prevent the cron job execution, if it is already running

Question

I have one php script, and I am executing this script via cron every 10 minutes on CentOS.

The problem is that if the cron job will take more than 10 minutes, then a

Answer 1

I was running a php cron job script that dealt specifically with sending text messages using an existing API. On my local box the cron job was working fine, but on my customer's box it was sending double messages. Although this doesn't make sense to me, I double checked the permissions for the folder responsible for sending messages and the permission was set to root. Once I set the owner as www-data (Ubuntu) it started behaving normally.

This might mot be the issue for you, but if its a simple cron script I would double check the permissions.