Something

kwzs:~# su kevin -c startx&
[1] 19720
kwzs:~# xauth:  creating new authority file /home/kevin/.serverauth.19721
X: user not authorized to run the X server, aborting.
xinit:  Server error.
Couldnt get a file descriptor referring to the console

[1]+  Exit 71                 su kevin -c startx