[Bug 1880409] [NEW] Prompting for change to sshd_config might cause lock-out from upgrade process

[T Jeske]

Public bug reported:

Upgrading to a new release is often done with do-release-upgrade. If you
do this via SSH, this probably runs in a dedicated "screen" session. At
some point you might be asked to replace your current "sshd_config" with
the package maintainer's one. While sitting at this prompt, you can't
open a new SSH connection to your machine.

If you let the upgrade run in the background from a remote pc, you might
lose connection in the meantime. If the upgrade reaches this prompt, you
will not be able to log in and resume your upgrade with SSH, as sshd
won't accept connections. The port is opened and you can connect, but
sshd will immediately close the connection, without even prompting for
credentials.

If you have no other means but SSH to access your server (e.g. headless
vps), you won't be able to login again and might be forced to a
reinstallation (or some other form of recovery operation).

** Affects: ubuntu-release-upgrader (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: do-release-upgrade ssh sshd upgrade

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https://bugs.launchpad.net/bugs/1880409

Title:
  Prompting for change to sshd_config might cause lock-out from upgrade
  process

Status in ubuntu-release-upgrader package in Ubuntu:
  New

Bug description:
  Upgrading to a new release is often done with do-release-upgrade. If
  you do this via SSH, this probably runs in a dedicated "screen"
  session. At some point you might be asked to replace your current
  "sshd_config" with the package maintainer's one. While sitting at this
  prompt, you can't open a new SSH connection to your machine.

  If you let the upgrade run in the background from a remote pc, you
  might lose connection in the meantime. If the upgrade reaches this
  prompt, you will not be able to log in and resume your upgrade with
  SSH, as sshd won't accept connections. The port is opened and you can
  connect, but sshd will immediately close the connection, without even
  prompting for credentials.

  If you have no other means but SSH to access your server (e.g.
  headless vps), you won't be able to login again and might be forced to
  a reinstallation (or some other form of recovery operation).

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