Ubuntu doesn't start, with a message 'Started GNOME Display Manager. Dispatcher Service... system changes.pp link was shut down'
Solution 1:
Solved! In recovery mode after enabling networking I selected dpkg - Repair broken packages, and then in root shell I used apt update and then apt dist-upgrade and this seems to have solved the problem. I'm not sure why it worked, but it worked.
Solution 2:
For a future user, if above doesn't work, try below method:
mv /var/lib/gdm3 /var/lib/gdm3.old
Or, if in case, you don't want to keep OLD, you can delete them (not recommended)
rm -rf /var/lib/gdm3/*
rm -rf /var/lib/gdm3/.[a-z]*
This should fixed the issue.