For the longest time after installing KDE in Ubuntu, my login screen became too big to fit my screen. The resolution was permanently set to 1600×1200. I tried everything to change it back to 1280×1024 and nothing worked. I searched the Ubuntu Forums, Googled my head off, and eventually gave up.
Today, I decided to try again with different keywords and found the solution on the Ubuntu Forums.
Edit your /etc/X11/xorg.conf file:
sudo gedit /etc/X11/xorg.conf …and remove all 1600×1200 references (or the offending resolution) under the Section “Screen”. Perfect!
UPDATE (2008.01.29): Only remove all the offending resolutions if you do not plan on ever using them. I removed them all because I never change resolutions. And as Anne suggests in the comments below, changing your “Virtual” line to the correct resolution may also fix your problem. I say “may” because this had no effect in Ubuntu 7.10. It should work in Ubuntu 6.04 and 6.10. Anne suggests:
Choose the resolution you want for the login (say, 1280 x 1024)
edit your xorg.conf file.
In the Section “Screen”, SubSection “Display”, you have two entries:
Modes and Virtual.
For the login, X will default to the first resolution defined in the “mode” entry. Thus, you must select the resolution you want (say, “1280×1024@60″) and move it at the first position.
Next, the “Virtual” entry is used to have a larger desktop resolution than screen resolution (you can reach the zones “outside the screen” by moving your mouser pointer to the edges). Your Virtual section should have the same size you want for the login resolution (say 1280 1024).
Thank you Ubuntu Forum Users!