Backup partition is locked and will not unmount
There is a known incompatibility when cPanel runs on CloudLinux under Centos 5.X. After a nightly backup runs or a restore runs, the backup partition will get stuck in an active lock. The next time you perform a backup or a restore, you will see an error similar to the following:
[backupmount] Cannot umount: /backup. This mountpoint is still in use and has an active lock
mount: /dev/sdc1 already mounted or /backup busymount: according to mtab, /dev/sdc1 is already mounted on
Then check Backup partition is locked and will not unmount
In order to resolve this, you will need to perform the following commands as root
mount -r /backup
mount -o remount,rw /backup
umount /backup