Disable display manager on boot

On robots that is normally without a screen, there is no need to run a display manager and a graphic user interface.

This will save some memory and start less processes.

inspect /etc/init, there is a configuration entry for the installed display manager, e.g.

gdm.conf (gnome ubuntu)
kdm.conf (kubuntu)
lightdm.conf (xubuntu)

To start the display manager and graphic user interface when needed only, make a manual override file for the display manager:

sudo bash
echo "manual" > /etc/init/gdm.override
echo "manual" > /etc/init/kdm.override
echo "manual" > /etc/init/lightdm.override
exit

After reboot, there will be a text login only. To (re)start the display manager (graphic login screen) use the command

sudo gdm     or
sudo kdm
sudo ligntdm

if you need failsafe boot and use the roor shell, you will need to remount the disk in rw mode to fix problems

mount -n -o remount,rw /