Cannot boot into desktop after purging GNOME3 PPA

Question

I am dual-booting a C2D laptop with W7 x64 and Ubuntu 12.10 x64.

After using the GNOME3 PPA and getting a bit wary of the increased system instability, I tried to downgrade to the standard 12.10 AMD64 components. I installed ppa-purge and issued the command sudo ppa-purge ppa:gnome3-team/gnome3, accepting the solutions offered.

However, instead of running the following additional commands

sudo apt-get update
sudo apt-get dist-upgrade
sudo apt-get install --reinstall ubuntu-desktop

I stupidly rebooted the machine. Now I can't boot into the partition. I tried the following things in Recovery Mode:

1. Attempted to launch to root and then issue the above (missing) commands, but it gave me some error regarding not being able to write to /var/apt/*something* (sorry but I don't remember the exact locked path),
2. Attempted to launch with the 'Start Networking' (or similar) option, but nothing happens. The system isn't frozen here, pressing the power button here shuts down the machine as expected.

How do I restore my Ubuntu partition without losing any data?

Answer 1

When you reboot as root, you need to issued the command

mount -o remount,rw /

To to make the disk writable (it's in a read-only state to begin with).

Then you can issue the command:

apt-get install ubuntu-desktop

Answer 2

One possible option would be to reinstall Ubuntu over your current installation. It should keep your files and many of your settings as well.

It is the easiest solution I can think of, albeit not the ideal solution.

You might wish to backup your important data after booting through your liveDVD or iveUSB before reinstalling.