This morning I found that most of my sites are either blank or having some error message such as this:
Warning: sessionstart(): open(/tmp/sess8c125544dd7a170503b284e020e59e09, ORDWR) failed: No space left on device (28) in /home/betaedel/publichtml/system/library/session.php on line 11

Trying to googling around the web for answer, and apparently most people say about /tmp is full.
But from what I see here, it's not really full yet
Device Size Used Available Percent Used Mount Point
/dev/vda1 30G 15G 14G 51% /
/usr/tmpDSK 1.2G 341M 795M 31% /tmp

Honestly I'm total newbie for the unix commands. I'm using Cpanel/WHM on CentOS 6.4, hoping that by Cpanel I dont have to deal much with console commands.
Any help or info is much appreciated.
Regards,

Hero Wijayadi