I moved my window manager from xfce to gnome today, and spent most of the day so far getting gdm3 to work. For a while, I was using two window managers, then narrowed it down to gdm3 and uninstalled the other one.
The login manager failed to come up, and for most of this morning I was stuck in a character console. In gnu/linux, strange things happen when you read a lot of documentation and error messages. I began to see artifacts that are in themselves hilarious, although after hours of poring through debug messages and error messages, I first thought I needed a long break. But no. The same phrase can be google’d, and others have reported seeing it, thus confirming my strange experience.
The error I saw was
We failed, but the fail whale is dead. Sorry.
So, what on Earth is a “fail whale”? It appears to mean that a part of the server that issues error messages, has died. Apparently, gdm3 itself didn’t die, since running ps showed that it was still running, although not running a login screen.
It turns out that the “fail whale” was a meme created by someone named Yiying Liu to refer to errors reported by Twitter. I guess I missed out on that meme.
Somewhere in the thicket of error and debug messages was a reference to the fact that /usr/share/gnome-sessions/sessions/ubuntu.session did not exist. I went to that location as root, and symlinked gnome.session to ubuntu.session.
ln -s gnome.session ubuntu.session
That appeared to be all that was needed. I was able to log on to a gnome desktop.