I have try Rajib Ghosh's method,but it doesn't work on my system. I found a new way to work out the problem. Using aticonfig command. Example: aticonfig --resolution=0,1024x768
You can using aticonfig --help to get more information. -- Login Screen Resolution https://launchpad.net/bugs/16472 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs