I use ubuntu18.04 for a while. Today, it suddenly crashed and can not boot again. Every time I boot, it can reach log in screen. When I input the password, the screen will turn into black. Then it will give the message below. Now, I cannot even go int grub.
Failed to start RealtimeKit Scheduling Policy Service
Failed to start Thunderbolt system servie1 Answer
If you can reach log-in screen it means that you've passed grub. One excludes the other. However your grub might be set to timeout really quick, so you don't even see it or it's even hidden in a way.
In such case the best way of getting into grub will be to use live cd.
First follow this tutorial to chroot into your Ubuntu installation and change the grub settings, so you can enter it:
While in chroot edit your /etc/default/grub and make sure you have GRUB_TIMEOUT set to something higher than 0.
GRUB_TIMEOUT=5
If GRUB_HIDDEN_TIMEOUT_QUIET=true is present, change it to GRUB_HIDDEN_TIMEOUT_QUIET=false.
Also, for debugging, it's useful to remove quiet splash options from GRUB_CMDLINE_LINUX_DEFAULT.
After changing /etc/default/grub` please update your grub with
update-grub2
make sure you do it inside chroot.
Then you can proceed with
