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/
If you see a lots of temporary files under /tmp/, it is time to check how often the system cleans this folder.
Usually the directory is cleared by default at every boot.
If you don't reboot that often, change the value of TMPTIME in /etc/default/rcS.
The default value is 0, meaning only at reboot.
Use 7 if you, for example, want the system to delete temp files once they turn one week old.