do-release-upgrade 18.04 LTS to 20.04 LTS failed, file system mostly read only. Final entry in main.log: ERROR failed to inhibit gnome-session idle

I attempted an upgrade from 18.04 LTS to 20.04 LTS. I ran do-release-grade on a direct terminal connection; I also had a Remmina RDP session running, and an SSH console open, just in case.

The update failed with a mass of text on the terminal window; if that text is available in full in some log file, I've been unable to find it.

The filesystem is read-only at this point, despite what mount says:

/home/.ecryptfs/moshe/.Private on /home/XXXXX type ecryptfs (rw,nosuid,nodev,relatime,ecryptfs_fnek_sig=5b0b5c4987d2da07,ecryptfs_sig=78f28cddca5488c4,ecryptfs_cipher=aes,ecryptfs_key_bytes=16,ecryptfs_unlink_sigs)

but

: touch xxx
touch: cannot touch 'xxx': Read-only file system

I cannot ssh, scp, etc. out of the system.

The files in /var/log/dist-upgrade include main.log. The final lines are:

2021-08-17 09:09:08,281 DEBUG failed to determine user upgrading
2021-08-17 09:09:08,282 ERROR failed to inhibit gnome-session idle

The parts of apt.log I am able to see -- "less" does not work, only "cat" -- show update logs, and lspci.log contains nothing odd.

The terminal window that contained the update won't scroll back -- it's a direct console window outside the GUI.

Transcribing what I can see:

File "<frozen importlib._bootstrap_external>", line 674, in exec_module
File "<frozen importlib._bootstrap_external>", line 780, in get_code
File "<frozen importlib._bootstrap_external>", line 833, in get_data

Original exception was:
Traceback (most recent call last):
File "/tmp/ubuntu-release-upgrader-rxudi66p/focal", line 8, in <module>
File "/tmp/ubuntu-release-upgrader-rxudi66p/DistUpgradeController.py", line 238, in main
File "/tmp/ubuntu-release-upgrader-rxudi66p/DistUpgradeController.py", line 2092, in run
File "/tmp/ubuntu-release-upgrader-rxudi66p/DistUpgradeController.py", line 1263, in doDisUpgradeFetching
File "/tmp/ubuntu-release-upgrader-rxudi66p/DistUpgradeController.py", line 1547, in abort
File "/usr/lib/python3.6/shutil.py", line 245, in copy
File "/usr/lib/python3.6/shutil.py", line 121, in copyfile
OSError: [Errno 30] Read-only file system: '/etc/apt/sources.list'

My guess is, at this point, a good solid reboot would clear /tmp and remount my filesystems, at which I could try again without the distraction of any remote sessions. Rather that risk that -- and possibly wipe /tmp files that would prove useful for debugging -- I thought I'd ask here first.

Questions

• What went wrong, and how can I avoid this problem in the future?
• Should I write a bug report about this if a remote session turns out to be a fatal error?
• Should I simply reboot? It not, what are the next steps?

The latter question is the most important from my perspective.

Late note: I'm not certain I can access my terminal windows any longer, and may have to reboot by default.

EDIT 1: For unknown reasons, I'd lost the ability to control any direct terminal screen, and remote SSH sessions failed. Without that, I decided to bite the bullet and reboot.

On reboot, the system came up sane in 18.04 LTS.

I'm now attempting to do the update. The software-updater graphical tool updated multiple files, then failed to complete some. An attempt to run do-release-upgrade demanded that I upgrade what I could separately, and I'm running into problems there. I will continue to update this ticket when I can.

EDIT 2: My repositories point at focal now instead of bionic. I'll need to undo this -- I'll likely add both focal and bionic repos in order to find the correct updates.