If you have 1000s of accounts on cpanel, you would probably get the error message
The /usr partition on this server is running out of disk space. WHM operation has been temporarily suspended to prevent something bad from happening. Please ask your system admin to remove any files not in use on that partition.
Here, you will left alone to find what files are taking too much space on the /usr partition
If you have ASSP or some kind of Antispam Engine installed it would take logs of space for storing the messages & logs
First, Login to ssh
use the below command
du -h --max-depth=1 /usr/
If you find any specific folder taking more space, you do denote the specific folder by
du -h --max-depth=1 /usr/local
here you can increase depth to 2, 3 & etc.. to see the space used in depth.
To sort the foldersize in ascending order user
du -h --max-depth=1 /usr/ | sort -n -r
Once you have found, You can remove the logs of cpanel, apache, assp & etc…