Since other posts suggest this, I should mention that I cannot run dpkg --configure -a, even after killing the process.
In any case, the Distribution Upgrade window blacked out, and when I try to close it, I get the following message... after which I still can't close it.
Application ubuntu-release-upgrader is not responding
You tried to close window "Distribution Upgrade" from application "ubuntu-release-upgrader" (Process Id: 2414) but the application is not responding.Do you want to terminate this application?
Warning: Terminating the application will close all of its child windows. Any unsaved data will be lost.
I tried killing the process from the command line kill -9 2414, I'm not sure it did. Then I ran dpkg --configure -a and I got that it's been used by another process.
dpkg: error: dpkg status database is locked by another process
I've seen other posts where they just remove the look. Is this safe to do?
How should I proceed to contain the damage?
ps aux | grep apt. If it is killed , you may remove the lock files then start over the upgrade.