How to fix error: The system failed to create the temporary file /var/tmp/ because of an error: Read-only file system

lsof /tmp

Then umount /tmp and /var/tmp:

umount -l /tmp
umount -l /var/tmp

Then remove the corrupt partition file:

rm -fv /usr/tmpDSK

Then create a nice new one:

/scripts/securetmp

(from Cpanel forum & User Chirpy)