Tente isso e comece apenas no texto:
Abra um terminal
Pressione Ctrl + Alt + T
Execute:
exec sudo -i
systemctl disable display-manager.service
systemctl set-default multi-user.target
reboot
Deve começar no terminal sem ambiente gráfico.
Como você o reverteria ao normal, embora se quisesse voltar?
Abra um terminal
Pressione Ctrl + Alt + T
Execute:
exec sudo -i
systemctl enable display-manager.service
systemctl set-default graphical.target
reboot
Comparação de SysV Runlevels com alvos systemd
Runlevel ----- Target Units -------- Description
0 runlevel0 -- poweroff.target ----- Shut down and power off the system.
1 runlevel1 -- rescue.target ------- Set up a rescue shell.
2 runlevel2 -- multi-user.target --- Set up a non-graphical multi-user system.
3 runlevel3 -- multi-user.target --- Set up a non-graphical multi-user system.
4 runlevel4 -- multi-user.target --- Set up a non-graphical multi-user system.
5 runlevel5 -- graphical.target ---- Set up a graphical multi-user system.
6 runlevel6 -- reboot.target ------- Shut down and reboot the system.