I have a cPanel Server with 4GB of Ram and 4GB of /tmp space. I always get this error:
Will this cause slow performance? and can I delete everything?
Drive Critical: /tmp (/var/tmp) is 95% full Drive Critical: /usr/tmpDSK (/tmp) is 95% full
No, you definitely can't delete everything in there. /tmp is where the system stores its temporary files when it's running.
What you can delete depends on what's running on the server.
I would recommend looking at the file list and finding out what's writing so much to your /tmp folder.
If these items exceed your technical skillset, I'd recommend contacting your reseller account's technical support or contracting someone who can assist you further.