when the screen locks while upgrading ubuntu, login is not possible anymore

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We are sorry that we do not always have the capacity to look at all reported bugs in a timely manner. There have been many changes in Ubuntu since that time you reported the bug and your problem may have been fixed with some of the updates. It would help us a lot if you could test a current, supported, Ubuntu version.

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[Expired for update-manager (Ubuntu) because there has been no activity for 60 days.]

This just happened to me while upgrading from 17.04 to 17.10..... It may be hard to replicate, but if the screen locks at the wrong moment, after the system has started updating packages it leaves it in a state where it cannot be unlocked.

I was left with a locked system, and an incomplete upgrade which I am still attempting to repair manually.

See attached image... this did not recover to a working state, and I was forced to kill the X session / dpkg components after waiting 12 hours... and attempt manual repair of the system.