Run Ubuntu without GUI

Edit grub file:
$ sudo vi /etc/default/grub

change this line:
GRUB_CMDLINE_LINUX_DEFAULT=

Values:
for GUI, GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
for Text mode, GRUB_CMDLINE_LINUX_DEFAULT="text"

Then run
$ sudo update-grub


And restart the machine.