I foolishly did an update to my Lubuntu.
Now I have no GUI and can only boot into root command line.
What can I do to get my GUI back ?
Is there any hope ?

If possible back up any important data, and do a fresh install, is often the easiest and quickest way of fixing such major problems, of course if you have done a full backup before doing the upgrade you can just restore that.

When you boot the thing boot to recovery mode. At the end of that you should get a root prompt (#). At that prompt;
This should configure any packages that were not fully configured if possible.

If you get errors at the end of that proceedure do;
which is the command to fix broken packages.

If that doesn't work we will need the output from the two commands above to see what the problem is. So write the whole ordeal down completely.

This problem seems to be confined to one account only.
I have two accounts, Able and Bubble. I never used Bubble,
so it is just fine. Under Able I did everything, including
the bad update. A background screen displays, but no icons
and no program menus. Press the left mouse button and you
get this small list of program menus, but only xterm starts.
This is good, because in xterm I can become Root and was
able to remove /usr/local/lib/libz.so.1.2.8 One of the
many "System Errors" messages pointed to this libz.so.1.2.8
as BAD and told me to remove it. I did but nothing was solved.
None of the other "System Errors" messages told me ANYTHING !

In Root in xterm I did dpkg --configure -a Nothing happened.
apt-get -f install said:
Reading package list ... Done
Building dependency tree...
Reading state information ... Done
0 upgrade, 0 newly installed, 0 to remove and 0 not upgraded
But it did nothing useful.

I don't understand any of this.
All I really want from account Able is:
1.... all the emails, sent and received, in Thunderbird
2.... my bookmarks in Firefox
Can anyone tell me how to do this using the command line in xterm ?

The rest of the files I want to save I can do so from xterm.
I have a Debian OS on the computer and both Lubuntu and Debian
use ext3 file systems, so I can shift programs over to store
in a directory in Debian.
Since I have no idea what is wrong with account Able, I have no
confidence that account Bubble won't go bad too.
Thank you all for your help. I didn't cause this and I don't
know how to fix it.

Yes. The recovery of those files is simple and putting them in another install or account is easy.

From what you say it really doesn't sound like the package upgrade is the problem. You have 2 accounts and one works. If the install was screwed it would affect all accounts.

What it sounds like is a screwed account. This is most likely in your ~/.foo files commonly known as "hidden" files. These are your user configuration files. These are the files, also, where you will find your TB and FF user account files.

Taking FF as an example for the function of all those files; they make it possible for Able and Bubble to use the same FF install but when Able logs in all the configuration; home page, bookmarks, font size, cookie policy and so forth are those Able set up. Bubble may have a completely different configuration including some eyecandy addon or video download addon enabled, want all cookies he can get, and font half the size of Ables. Both will have their own bookmarks.

As for getting your book marks; hit Ctrl + h in your file manager. This will make your ~/.foo files visible. Go to /able/.mozilla/firefox/<alphabet soup>.default/bookmarkbackups. Grab the latest one by date and you have the complete set as used the last time you made a change.

Grabbing the entire "<alphabet soup>.default" will give you the complete configuration for FF. Some of us have several installs and use the same file for all of them so that our browser is the same no matter the install we are on. I would not recommend this in your case and will get to the reason shortly.

For TB the files you need are in /home/able/.thunderbird/<moresoup>.default. Here I would just take the whole thing because sorting it out is a pain to describe and I am lazy today.

What you should try to do is, probably using a Live Session, is go in to Ables account and first create a new directory ~/HIDDEN. If you are not familiar with ~ then ~/HIDDEN means /home/able/HIDDEN. Just a lot easier to write.

Then cut/paste ALL YOUR ~/.foo files to ~/HIDDEN except for ~/.Xauthority and ~/.ICEauthority. Just clear the buggers out. Reboot. This should regenerate all needed ~/.foo files to the correct default just like a new install would have but a lot quicker and easier.

If it still fails to boot go back in and, again remove all ~/.foo files and this time take them all. Leave none. Reboot.

If it still fails to boot but Bubble is booting go to your Live session again and edit the /etc/group file so that the lines starting with;
adm
sudo

Have able and bubble similar to;
There should also be 2 lines similar to;
add to them so they look like;
Reboot try to log in as able. If this still doesn't work try bubble and see if bubble has admin permissions. If so use bubble. If not save those ~/.foo files for able that you put in ~/HIDDEN and if you like any of the configuration for bubble grab them too.

Reinstall.

The reason for not using the FF complete config file is simply because one or more of your confige files, probably not FF but why take chances, is what is most likely causing your problem.

If you can log in and function with the new default regenerated ~/.foo file this theory is proven. You can then, carefully replace the those new files with the olde ones or portions of the old ones, one at a time. Reboot or log out/log in between transplants to see which work. One at least should screw you again but you know which it is; the last one you transplanted, and can just boot in as bubble and remove it.

With bubble being a member of group able and able being a member of group bubble you shouldn't have any trouble with either user editing files I think. Not sure I remember how Ubuntu deals with permissions of the groups associated with users. If not do it from a live session.

Following your advice Widget. Saved my bookmarks and email,
then attempted to save all hidden files into HIDDEN.
Two problems: I have no .ICEauthority
I have 105 files of .goutputstream- 6 digits of crud
example .goutputstream.OKRY6W
yes, I counted them ! 105 of them.
What are they ? Where did they come from ?
Should I just continue as you have already written or is this yet
another problem that need to be handled ?
Thank you very much for helping me save my bookmarks and email !

I am not sure why you have the package that creates the goutputstream files. It is a Gnome dev package and I don't use Gnome. It is probably included by default in Ubuntu, and maybe with all Gnome installs regardless of distro, as an add to bug reporting. If you were to remove those files they would be regenerated when you log in.

Have you compared that directory with the same directory in your other account?

As to ICEauthority this is another one that you should check for in your other account. If it doesn't exist in the other account, which works, I wouldn't be too concerned about it. Ubuntu handles security in a different manner, poorly in my opinion, than other distros. They may just not use it.

If the other account does have that file and you have rebooted into the faulty account then this would indicate not a general system problem but would definitely indicate a fault in the faulty account setup. This would simply reenforce that trying to get rid of all user config files and having them regenerate is a good place to start.

It may be that you need to create a new user. I am not at all sure how one user account could be screwed by a package upgrade. I could see it if both were screwed. I think there has to be something in the ~/.foo files for that account for it to be bad. But if the account config files are not the problem you would need a new account to replace it. If your install has a gui for "managing accounts" do not use it for doing so.

Which brings up another question; Have you ever used such a tool to mess with your accounts?

If something like this happens, check contents of .xsession-errors in your home directory. lxde uses it (although could give more information in my opinion).

Check also what is in your desktop session settings (under preferences)

Check what is in .config/lxsession/LXDE/autostart.

This looks a little bit like something in the autostart is messed up.

I've decided to download the newest Lubuntu and to replace the old version
with it. Lubuntu has always been a reliable and fun distro to run.
Thank you all for all your help and I have tied many of the ideas given.
I especially appreciate Widget telling me how to save my bookmarks and email.
It became obvious this problem is beyond my knowledge so I concentrated
on saving all valuable files to a different partition and to USB sticks.
I hope I got them all.
I should have spent more time saving important stuff to a different
partition back when Lubuntu ran good.
Now, on to the future and the new Lubuntu ! This problem is SOLVED.