How do I boot into the console and then launch the Ubuntu desktop from it?

To return to the login screen

Press Ctrl+Alt+F7 to return to the login screen. You can exit your terminal session on tty1 by typing exit before you do that.

Doing startx -- :1 will start another X session under terminal tty1, logging you in directly (use :2, etc. for even more displays). Note that logging into multiple sessions as the same user is not recommended and could lead to system instability.

To skip the login screen completely, boot into the console and then start the GUI, you must modify GRUB:

• sudo nano /etc/default/grub
• Change line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" to GRUB_CMDLINE_LINUX_DEFAULT="text"
• Ctrl-X, press Y and then Enter to save and exit.
• sudo update-grub
• Reboot and you should come up directly in tty1 -- no need to press Ctrl-Alt-F1.
• Login, and then startx to boot into the default desktop, or
  • unity for Unity
  • unity-2d-shell for Unity 2D
  • gnome-shell for Gnome
  • sudo service lightdm start to get the login screen (if you fix it :)

To skip the login GUI without using Ctrl+Alt+F1, simply do the following:

• sudo vi /etc/default/grub
• Press i to enter into vi edit mode.
• Change the line that reads GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" to GRUB_CMDLINE_LINUX_DEFAULT="text"
• Uncomment the line which reads #GRUB_TERMINAL=console by removing the leading #
• Press Esc to exit vi edit mode.
• Type :wq to save the change made to the /etc/default/grub file and exit vi.

• Update /boot/grub/grub.cfg to have your change apply by running sudo update-grub

  If your computer uses systemd, you must tell systemd to skip the default login GUI thus:

  sudo systemctl enable multi-user.target --force
  sudo systemctl set-default multi-user.target
  

• Reboot your computer: sudo reboot

Now, the login GUI will never show up.

Once you're in the terminal, run sudo systemctl start lightdm to start the default desktop.