[Bug 1959475] Re: "machinectl shell" connections immediately terminated

[Matthieu Clemenceau]

** Tags added: foundations-todo

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https://bugs.launchpad.net/bugs/1959475

Title:
  "machinectl shell" connections immediately terminated

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Focal:
  Fix Committed

Bug description:
  [Impact]

  This bug prevents users on Impish and newer from connecting to Focal
  systemd containers using `machinectl shell`. This limits users ability
  to manage containers spawned with systemd-nspawn.

  [Test Plan]

  On a Jammy host, do the following:

  * Install systemd-container and debootstrap if necessary:

    $ sudo apt install debootstrap systemd-container

  * Create a Focal filesystem for the container:

    $ sudo debootstrap --arch=<arch> focal
  /var/lib/containers/lp1959475/

  * Launch the container:

    $ sudo systemd-nspawn -D /var/lib/containers/lp1959475/ --machine
  test-container

  * Inside the container, set a password for root and then exit:

    $ passwd # Enter password when prompted
    $ exit

  * Re-launch the container with -b option:

    $ sudo systemd-nspawn -D /var/lib/containers/lp1959475/ --machine
  test-container -b

  * In a separate terminal window, try to connect to the container:

    $ sudo machinectl shell test-container

  * Observe the "Connection to machine test-container terminated" error
  message.

  [Where problems could occur]

  The patch expands the case where the TERM variable is inherited from
  PID 1 when building an execution environment, e.g. for a container. If
  problems were to occur, it would be related to the value of TERM in
  environments forked off of PID 1.

  [Other Info]

  This bug occurs when trying to connect to a Focal container from e.g. a Jammy host. For SRU verification, the container
  should be Focal, and the host should be Jammy. The -proposed package should be installed in the Focal container.

  [Original Description]

  The command "machinectl shell" does not work in systemd
  249.9-0ubuntu2:

  $ sudo machinectl shell ns-xxx
  Connected to machine ns-xxx. Press ^] three times within 1s to exit session.

  Connection to machine ns-xxx terminated.

  The issue seems to be described here:
  https://forum.manjaro.org/t/the-machinectl-shell-command-stopped-working-after-systemd-upgrade-to-250-2-1/99899
  https://github.com/systemd/systemd/issues/22234

  and solved here:

  https://github.com/systemd/systemd/commit/e8cf09b2a2ad0d48e5493050d54251d5f512d9b6

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