17.10 to 18.04 upgrade freezes during boot

Try logging in to your default desktop environment from the tty virtual console. The virtual console can be accessed by pressing the keyboard combination Ctrl+Alt+F3 after the computer gets stuck when booting it. Login to the virtual console with your username and password and run the following command.

sudo systemctl start graphical.target

If that doesn't work, switch the login display manager from gdm3 to lightdm. LightDM is a more lightweight login display manager than gdm3.

sudo apt install lightdm   
sudo dpkg-reconfigure lightdm 
sudo reboot  

sudo dpkg-reconfigure lightdm will open up a new window allowing you to select lightdm as the default login display manager. Use the arrow keys to select lightdm, press the Tab key to put the focus on <OK> and press Enter. Then reboot by running sudo reboot

Try booting from Xorg instead of Wayland. Edit /etc/gdm3/custom.conf with sudo nano /etc/gdm3/custom.conf, uncomment #WaylandEnable=false so it is WaylandEnable=false and run sudo dpkg-reconfigure gdm3 # select gdm3

If that doesn't work either see if you can at least switch to text mode (for troubleshooting purposes) with no GUI stuff like the X server running.

sudo systemctl start multi-user.target  

Turns out that the problem isn't a gdm3 vs lightdm problem. It's a gdm3/wayland problem with older Intel GPU's. To fix...

In terminal...

• cd /etc/gdm3 # change directory
• sudo pico custom.conf # edit this file

Find and change:

#WaylandEnable=false

To this:

WaylandEnable=false

Save the file.

• sudo dpkg-reconfigure gdm3 # select gdm3 DM

Select gdm3 and OK.

• reboot # reboot the computer