My Gnome installation (Ubuntu 18.04) appears to be broken. After I log in, it displays some log messages and hangs. The last message says in effect "Starting Gnome." I've tried removing the proprietary graphics drivers and switching to a radically different graphics card; neither measure helped.
I assume, but am not sure, that Ubuntu itself is intact. It appears to work just as it should when I boot to rescue mode.
How can I repair my system with a minimum of disruption?
I found instructions for installing Gnome...
...and for repairing Linux...
The first set of instructions are admirably simple: install a few packages. It seems to me that I should be able to uninstall the broken Gnome by removing the same packages in reverse order, but I don't know whether that is the best approach; I suspect that after I reinstall Gnome I'll have to reinstall all of my graphic applications. I'd prefer instructions specifically for repairing Gnome, but I haven't found any.
The latter instructions assume a system that functions in rescue mode, but don't distinguish between "repairing" Ubuntu and Gnome, so I'm not sure just what they're meant to accomplish. The system's useless as it is, but I'd rather know what this experiment is supposed to do before I undertake it.
Perhaps I should just restore the Linux partition with dd. If I save my current data first I won't lose anything. The only disadvantage is that I'll have to reconstruct whatever software I installed or reconfigured after my last backup.