Ubuntu 12.04 can be started in console mode (without GUI) by adding the file
/etc/init/lightdm.override with the content
echo manual | sudo tee -a /etc/init/lightdm.override
When I start Ubuntu in console mode, however, there are three odd things happening:
.xsessionfile (rather than
.Xmodmapwith key mappings is no longer read.
When I exit X Windows the computer hangs with a black screen.