Last week I had a server that was hosting over 50 sites stop responding correctly.
The source of the problem was that the server had used up the available quota of inodes. In this directory were 800,000 old php session files:
I think that cyberpanel should add a cron script that runs either every day or every week that delete all session files older than 7 days.
This will prevent this issue from occurring again for all of us.