If you get an error similar to:
Warning: session_write_close() [function.session-write-close]: Â open(/tmp/sess_1234567890, O_RDWR) failed: Permission denied (13) in /script
it would imply that your /tmp folder is not writeable by php. Â The /tmp folder is a globally shared writing location and the permission should be set to 1777. This allows everyone write access to it, but will prevent cross-user account writing (so users cannot write other's files).To fix the above error, type:
chmod 1777 /tmp