[Bug 2047082] Re: upgrading openssh-server always shows error: rescue-ssh.target is a disabled or a static unit not running, not starting it.

[Colin Watson]

https://salsa.debian.org/ssh-
team/openssh/-/commit/da06b7ef32c20de4dd18cd578025d96a9221984b

** Changed in: openssh (Ubuntu)
       Status: New => Fix Committed

** Changed in: openssh (Ubuntu)
     Assignee: (unassigned) => Colin Watson (cjwatson)

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Title:
  upgrading openssh-server always shows error: rescue-ssh.target is a
  disabled or a static unit not running, not starting it.

Status in openssh package in Ubuntu:
  Fix Committed

Bug description:
  In our project we regularly build Ubuntu VM images for current 23.10
  (stable). In https://github.com/cockpit-project/bots/issues/5691 we
  ran into an upgrade failure of openssh-server. It starts with the
  current cloud image and then apt upgrades it, with
  "DEBIAN_FRONTEND=noninteractive". openssh was updated a few days ago
  indeed:

    Setting up openssh-server (1:9.3p1-1ubuntu3.1) ...
    Creating SSH2 ECDSA key; this may take some time ...
    256 SHA256:UqrRSpQNM7SIixVivYP/WwZRjt7Sv89P31W/Gxaf+Z8 root at ubuntu (ECDSA)
    Creating SSH2 ED25519 key; this may take some time ...
    256 SHA256:hy9AEDydfnZeY9nf9P4Sb90kx39Oqr101A6tz5j4RQw root at ubuntu (ED25519)
    rescue-ssh.target is a disabled or a static unit not running, not starting it.
    Could not execute systemctl: at /usr/bin/deb-systemd-invoke line 145.
    dpkg: error processing package openssh-server (--configure):
     installed openssh-server package post-installation script subprocess returned error exit status 1

  I.e. of course that security update itself [1] didn't introduce the
  regression, but earlier VM builds just didn't have a pending openssh
  update -- looks like this has been a luring upgrade trap in the
  release already.

  As a first naïve reproducer I tried

    apt update
    DEBIAN_FRONTEND=noninteractive apt update openssh-server

  on our current VM (with the release version 1:9.3p1-1ubuntu3), and
  that worked fine. Same with installing all 9 available packages.
  rescue.target is loaded/inactive/static, as it should be. Updating
  without DEBIAN_FRONTEND does show me a conffile prompt about
  /etc/ssh/sshd_config, which is justified as we do modify the config:

    # Allow root login with password
    sed -i 's/^[# ]*PermitRootLogin .*/PermitRootLogin yes/' /etc/ssh/sshd_config
    # Prevent SSH from hanging for a long time when no external network access
    echo 'UseDNS no' >> /etc/ssh/sshd_config

  this also leads to a merge conflict. However, I suppose all of that is
  tangential to the rescue-ssh.target issue. In all my interactive
  upgrades, it seemed to handle that just fine:

    Setting up openssh-server (1:9.3p1-1ubuntu3.1) ...
    rescue-ssh.target is a disabled or a static unit not running, not starting it.

  So this seems to be related to the first-time installation of openssh-
  server -- it is part of the cloud image, but it does the host key
  generation during our image builds.

  So reproducing this is a bit tricky, but aside from that: Why does it
  even do this in the first place?

  # Automatically added by dh_installsystemd/13.11.6ubuntu1
  if [ "$1" = "configure" ] || [ "$1" = "abort-upgrade" ] || [ "$1" = "abort-deconfigure" ] || [ "$1" = "abort-remove" ] ; then
          if [ -d /run/systemd/system ]; then
                  systemctl --system daemon-reload >/dev/null || true
                  if [ -n "$2" ]; then
                          _dh_action=restart
                  else
                          _dh_action=start
                  fi
                  deb-systemd-invoke $_dh_action 'rescue-ssh.target' >/dev/null || true
          fi
  fi

  It feels like the postinst should *never* try to start rescue-
  ssh.target. That's an alternative boot mode, and should never run un
  multi-user.target, isn't it?

  [1] https://launchpad.net/ubuntu/+source/openssh/1:9.3p1-1ubuntu3.1

  DistroRelease: Ubuntu 23.10
  PackageVersion: openssh-server 1:9.3p1-1ubuntu3.1

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