Is it Safe to Delete Files From /var/tmp?

Solution 1:

Filesystem Hierarchy Standard

5.15 /var/tmp : Temporary files preserved between system reboots

5.15.1 Purpose

The /var/tmp directory is made available for programs that require temporary files or directories that are preserved between system reboots. Therefore, data stored in /var/tmp is more persistent than data in /tmp.

Files and directories located in /var/tmp must not be deleted when the system is booted. Although data stored in /var/tmp is typically deleted in a site-specific manner, it is recommended that deletions occur at a less frequent interval than /tmp.

Yes, you can remove all files in /var/tmp/.

But 18Gb is far too much. Before deleting these files do have a look at what it holds and see if you can find a culprit. Otherwise you will have it at 18Gb again soon.