How to avoid Rsync Endless Loop

Rsync is a great command-line sync tool, that allows fast replication from one web server to another.

If you are running more than one Rsync command in a cronjob, replicating several folders into a target machine, watch out for the Rsync endless loop bug.

There are two steps you can take to avoid this:

Step 1:

Consider this scenario:

Destination machine B has these two cronjobs, set to run every 5 minutes:


Since the folder /usr/home/something/ is also included by the first cronjob, this can easily cause the infamous Rsync endless loop bug.

The fix, add an --exclude to the first cronjob, like this:


Step 2:

If it takes more than 5 minutes for Rsync to complete, before the next instance runs, you're in trouble.

To be safe, write a php script that will check if the Rsync daemon is running, prior to launching another one.