If your server is approaching 99% disk space, your users may be aware of this before you are. At the 1% free margin, the following error will pop up when accessing certain features in cPanel and WHM:

Sorry for the inconvience!
The filesystem mounted at / on this server is running out of disk space. cPanel 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

While 99% may seem like a dangerous limit, servers nowadays are getting rather large. If you have a server with over 3T of disk space, that 1% free could be well over 100G of space – space that would seemingly become waste.

Until this limit is removed in a future release, you can actually trick cPanel into thinking that the server has more space available. The key is the cache files located in /root/.cpanel/datastore, specifically the file _bin_df_-P_-k_-l.

If you edit that file and change the occurrence of 99% to a lower value, you’ll see the restricted cPanel and WHM features return to normal. Keep in mind that the cache regenerates, so in some cases it may be appropriate to create a cron job to periodically change the file.

Of course, if 99% disk usage on your server leaves you with a minuscule amount of space, you’ll want to remove some files or add additional storage. The following articles may be useful:

• http://www.thecpaneladmin.com/11-ways-to-free-up-disk-space-on-a-cpanel-server/
• http://www.thecpaneladmin.com/huge-cpan-folder-home/
• http://www.thecpaneladmin.com/managing-multiple-hard-drives-cpanel/
• http://www.thecpaneladmin.com/manually-rearranging-accounts/

Thanks to my colleague Lee for sharing this tidbit of info