Considering installing eAccelerator and while looking around the eaccelerator.net website, I noticed the following:
Step 4. Creating cache directory
One last very important step is creating the cache directory that you configured in the previous step. The default value is /tmp/eaccelerator It's easy because it's writable to everyone, but it isn't very smart because on a lot of systems this directory is cleaned on reboot. A better place would be /var/cache/eaccelerator. Create the directory and make sure it's writable for the user eAccelerator runs under (usually the user which you webserver runs as).
A safe bet is making it world writable. A safer and cleaner way would be to change the owner of the directory to the same user PHP runs as (most of the time the same user as Apache or Lighttpd) and set 0644 permissions.
Is Atomic eAccerator set-up as default using /tmp/eaccelerator 0777/0644 with user apache? Is anyone using the /var/cache/eaccelerator option (or similar)?