Your /var directory has filled up and you are left with with no free disk space available. This is a typical scenario which can be easily fixed by mounting your /var directory on different partition. Let's get started by attaching new storage, partitioning and creating a desired file system. The exact steps may vary and are not part of this config article. Once ready obtain partition UUID of your new var partition eg. /dev/sdc1:
Reboot your system and you are done. Confirm that everything is working correctly and optionally remove old var directory by booting to some Live Linux system etc.