That was a bad evening, I upgraded my debian box and X failed to start throwing below errors.
6017.269] (EE) modeset(0): drmSetMaster failed: Permission denied [ 6017.269] (EE) Fatal server error: [ 6017.269] (EE) AddScreen/ScreenInit failed for driver 0
After spending hours I came to know latest X can’t run without root privilege now. We need to have legacy package of xserver to run X as non root user
sudo apt-get install xserver-xorg-legacy
then the wrapper config, so edit/create /etc/X11/Xwrapper.config to have the below two lines only.
X is back, What a relief .