Centos 7 'No Space Left on Device' error when transferring accounts using WHM

The accounts weren't transferring properly and it turned out to be we'd reached our inode limit. Here's how I arrived at that:

du -sh /

Showed 18G of space being used.

df -h

Also, showed 18G of space being used.

df -i /

Showed 100% of inodes being used.

Removed two accounts (one was the account I'd tried to transfer and the other was the account I suspected of being so resource intensive) and ran the lasty command again.

Showed 11% of inodes being used. Done. It was only the dev server so I wasn't worried, but rather than increase the drive space, I went for removing files.

Hat tip.