Having put /home on a separate partition when installing and then added another version of Ubuntu to a third partition and used the /home in common, I see the error of my ways. I want to put both /homes back in their OS trees and repurpose the old common 'home' partition.
I am trying to follow https://help.ubuntu.com/community/Partitioning/Home/Moving and How to undo move /home into /old_home?
I know the UUIDs of all partitions and can edit the fstab and #-ed the /home partition. Can't log into the normal GUI as 'cannot update ICEauthority file'. After restarting in recovery mode I see /home has no link to the far home folder. I can't make a new dir (RO file system) and can't useradd any username ('cannot lock /etc/passwd').
My problem is that my only user's home directory is a subdirectory of /home - where I want to move it to, and a link is already in operation with that username!
How do I clean this mess up without yet another reinstall, please?
mount -o remount,rw /in your recovery shell. Then, proceed as you already tried.