So I did
apt-get install fglrx
apt-get install fglrx-updates
And problem above disappeared. X Server running. But still cgminer does not see my 6850.
set@miner:~/cgminer-3.1.1-x86_64-built$ export DISPLAY=:0
set@miner:~/cgminer-3.1.1-x86_64-built$ ./cgminer -n
No protocol specified
No protocol specified
[2013-05-25 15:23:48] CL Platform 0 vendor: Advanced Micro Devices, Inc.
[2013-05-25 15:23:48] CL Platform 0 name: AMD Accelerated Parallel Processing
[2013-05-25 15:23:48] CL Platform 0 version: OpenCL 1.2 AMD-APP (1016.4)
[2013-05-25 15:23:48] Error -1: Getting Device IDs (num)
[2013-05-25 15:23:48] clDevicesNum returned error, no GPUs usable
[2013-05-25 15:23:48] 0 GPU devices max detected
[2013-05-25 15:23:48] USB all: found 12 devices - listing known devices
[2013-05-25 15:23:48] No known USB devices