Backup logs are the best place to start when diagnosing backup experience issues. To see your backup logs, access the command line using the instructions on Using Terminal To Access the Command Line. Then, enter the following command to see a list of your most recent backup logs:
$ ls -lt /usr/local/cpanel/logs/cpbackup/ | less
Next, open the backup file corresponding to the date you observed a backup failure or error using the example command below:
$ cat /usr/local/cpanel/logs/cpbackup/123456789.log
Carefully scroll through the output in Terminal and look for the specific output related to the error. When you find it, you now are in a much better position to troubleshoot the problem, and will have a specific error message to enter when searching support.cpanel.net for the answer. Aim to limit search queries to specific error codes or phrases.
Browse to Backup Configuration to see a detailed look at the backup configuration settings.