[Bug 2116874] Re: `do-release-upgrade` as CLI, run with DistUpgradeViewText, requires screen but does not declare dependency

[John Chittum]

** Also affects: ubuntu-release-upgrader (Ubuntu Questing)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/2116874

Title:
  `do-release-upgrade` as CLI, run with DistUpgradeViewText, requires
  screen but does not declare dependency

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

Bug description:
  Starting in Ubuntu 25.10 Questing Quokka, `screen` is not a part of
  default server installs, nor the ubuntu-server metapackage. `do-
  release-upgrade` when run via the CLI, will utilize the
  DistUpgradeViewText as the frontend, which sets `needs_screen=True`.
  This will run the current upgrade session in a `screen` session. By
  default on an Ubuntu server, this will run into issues starting in
  25.10

  1. in a fresh install of 25.10 Server, then upgrading to 26.04, screen will not be available, causing the upgrade to fail
  2. on upgrades, since `screen` is no longer seeded and a part of `ubuntu-server` metapackage, it will end up marked for removal. A user will likely then remove screen (unless they require it for personal reasons), thus rendering an upgrade to 26.04 not possible.
      a. this will _also_ occur in a world of rolling LTS to LTS. when upgrading from 24.04 to 26.04, screen will get marked for removal. This means if a user upgrades past 26.04, they will likely hit this scenario, with even greater time passed.

  I see two options, a short term patch and the long term fix which
  requires development work

  Option 1: add screen as a dependency

  list screen as a dependency for ubuntu-release-upgrader-core. NOTE --
  that ubuntu-release-upgrader-{gtk|qt} provided views are, as far as I
  can tell, unaffected

  This solves the short term problem, but is tantamount to putting
  screen back in by default. that's not a _terrible_ thing by itself,
  and my be "fine" by most people's estimations.

  Option 2: refactor to use tmux

  tmux is heavier than screen for this scenario, but it is installed by
  default as part of ubuntu-server metapackage. In addition, tmux should
  be added as a dependency (to ensure if we hit another such future
  scenario, we prevent immediate issues).

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