crashes under linux

[Phobios]

Hello everyone,
I am in need of some help. I am running oclHashcat-plus64.bin in Ubuntu 10.04. I have 2 HD6990 cards and am trying to crack a WPA/WPA2 password. Everything is running smoothly for a couple of minutes, then the whole computer freezes and needs to be restarted.

Before I start cracking I set the fans to 75%. This keeps the GPU cores to a maximum of 75C. I have a 1200W power supply and I have checked to make sure that the cards does not require that much power. They only reach around 800W. The power consumption drops to around 200W at the moment the computer freezes.

I have tried leaving one core out of it (-d 2,3,4), but the same thing happens.

The exact command I am running is:
./oclHashcat-plus64.bin -m 2500 fourwayhandshake.hccap wordlist.txt -n 80 -gpu-loops 4096 -r rules/perfect.rule

The computer is working fine otherwise. I can play games with it and I have mined bitcoins with it for many days in a row without any problems.

Does anyone have any idea of what is wrong or what I could try to make it work?

[atom]

with --gpu-loops 4096 you hold the kernel long time from returning to the OS. lower that number to maye 256 and try again if you can reproduce it.

[Phobios]

Turned the -n and --gpu-loops off alltogether and it works fine now. Wont get up to the same speed as when I had those options turned on. With the options it tested ~360k c/s, but without them I "only" get ~330k c/s. GPU load is mostly around 95%, but occasional dips to 70-80% occurs.

Thank you for your help.