Ubuntu升级后进入不了图形界面

更新Ubuntu后进入不了图形界面，用命令行登陆后执行startx, 提示：

Fatal server error:
Server is already active for display 0
If server is no longer running , remove /tmp/.X0-lock and start again

解决方法是重新设置xserver

sudo /etc/init.d/gdm stop 
sudo dpkg-reconfigure xserver-xorg 
sudo gdm start