upgrading gnome-session

[sgk at kleinmann.com]

This is just an FYI, in case you come across a user with a similar issue.

I use Debian's 'testing' distribution.  I usually update every few days.
 
Yesterday I updated my packages.  Something made me want to reboot (I think
I was testing something about the menu system and when it didn't work
as I expected, I hoped that maybe rebooting would help).

When I rebooted, I got past the login screen, but gnome never "did anything"
after that.  I simply saw a big blue screen with the usual background, but
with no menu bars, apps, etc.

I found nothing useful in 
~/.xsession-errors or in
/var/log/gdm3 or in
/var/log/Xorg.0.log or in
syslog or daemon.log, etc.

To check whether this was somehow a hardware problem, I then updated the 
software, etc., on another host which also used Debian/testing, but
which had very different hardware.  The other host upgraded smoothly
and had no problems.  However, there was a big difference in the output of 
'ps axf' between the two systems:  whereas my system was invoking twm as 
the window manager, the other system was using x-session-manager (which 
was gnome-session).  That's when I noticed that gnome-session had somehow 
been removed from my machine.  

When I tried to reinstall gnome-session on my host, I learned that it was 
missing some dependency, which I guess is why it had previously been 
removed.  To succeed with the installation of gnome-session,
I had to install all of these additional packages from the unstable
distribution:
gnome-session-common_3.4.2.1-1_all.deb
gnome-session-bin_3.4.2.1-1_amd64.deb
gnome-session_3.4.2.1-1_all.deb
gnome-shell-common_3.4.1-5_all.deb
gir1.2-mutter-3.0_3.4.1-4_amd64.deb
gnome-shell_3.4.1-5_amd64.deb

Even after that, my system still didn't work: the screen that appeared
after the login screen still had no windows/panels, etc.  Also, 'ps axf'
showed that gdm3 was still invoking twm instead of x-session-manager.

I reconfigured gdm3; still no luck.  

Finally I removed twm and reconfigured gdm3 again, and the system is now 
working again (although the screen looks more like it did before the 
move go Gnome3, but that's OK).

Maybe you already know about these issues with the migration of gnome-session;
if not, I hope this report saves you some time in case someone else has a 
problem with it.

Best regards,
Susan Kleinmann