There were more system updates, so I updated my (slow, 450 megahertz) system using the command-line-interface, using the following commands:
sudo apt-get update sudo apt-get dist-upgrade
I ran into two problems, but knowing these problems, I can avoid them.
The first problem, is that while I was doing the first command, the system was trying to find out if updates were available, so it had ownership of a lock that the "apt-get update" command needed. This resulted in the first step not successfully completing.
To get it to work, I had to run the update-manager GUI to where it reported the updates available, but use the "Remind Me Later" button to dismiss it. At that point, I could (in the terminal window) do the "apt-get dist-upgrade" command.
The second problem, was that after doing the "apt-get dist-upgrade", the CPU was still 100% busy for quite awhile (a minute?) afterwards even though control had returned to the command prompt. I entered the "top" command, and it showed there was a root process, named something like "update-xapi-index".
After awhile, CPU-usage went back to zero, so it was done. It took perhaps a minute.
So I guess the way I need to do this, is let the update-manager notify me of updates, and observe the available updates in the list, but instead of applying the updates in the GUI, click the "Remind Me Later" button, whereupon the update-manager exits, releasing its lock.
Then, I need to fire-up a terminal, and enter the
sudo apt-get dist-upgrade
command, and can monitor the progress of the system being updated.
When control returns to the command-prompt, I need to enter the "top" command to monitor the progress of the root processes associated with updating the system.
When that process completes (and CPU usage goes back to an idle state), the updates are done.
So I have a usable work-around for the problem with the update-manager, and I can keep using my 450 megahertz machine.