If an error message is received informing No space left on device.

mkdir: cannot create directory `folder’: No space left on device

To clean the disk, one suggestion is to hunt for big files.

This command searches for files larger than 50 MB under your current directory:

find . -type f -size +50000k -exec ls -lh {} \; | awk '{ print $9 ": " $5 }'

Check at least under the following directories:

/root/
/home/
/opt/
/tmp/