Server is not stable due to some (probably) hardware problems. It's crashing whenever it's given some workload. If I cannot find the reason and fix it, I will migrate the server to the Windows machine(hisui).
---update
Got another clue about the problem. It seems that the graphic adapter has been rogue. So I replaced.. Let's see how stable the sever becomes.
---update
Replacing the video card fixed the problem. Done.