[Bug 2052549] Re: 18.04 fails with "Unknown error" when attempting to update to the latest version of the installer.

[Dan Bungert]

Hi Peter, thanks for the report.

I retested this locally and wasn't able to see Subiquity trying to get
core22.  We have pinned working versions of Subiquity that are newer
than what's on the 18.04.6 ISO - a last supported build for Ubuntu
18.04.x, basically.  Would you mind retrying and see if you get better
results?  With luck this was just a temporary glitch and would also be
fine for you now.

** Changed in: subiquity (Ubuntu)
       Status: New => Incomplete

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Title:
  18.04 fails with "Unknown error" when attempting to update to the
  latest version of the installer.

Status in subiquity package in Ubuntu:
  Incomplete

Bug description:
  When using the 18.04.06 Ubuntu server installer, the installation
  process will prompt the user to update the installer to the latest
  version; The "Installer update available" step. This is because the
  18.04.06 installer runs version 21.08.02 of the installer. However
  this update process fails with an "Unknown error".

  The reason for this error seems to be that the 18.04.06 installer runs
  an older version of `snapd` that does not have the features required
  for the newer installer to work. More specifically the latest version
  of the installer requires the latest version of `subiquity`, which in-
  turn requires the core22 snap. The latest version of `subiquity`
  requires snapd >= version 2.55.5. This is reflected in the messages
  seen during an attempted update of the installer:

  ```
  Consider re-refresh of "subiquity"
  Download snap "core22" (1033) from channel "stable"
  ```

  Testing shows that it is either extremely difficult or impossible to
  update the installation environment to use the appropriate version of
  `snapd` without a restart of the instance; Which defeats the purpose
  of the live installation.

  A tested workaround is to use the installer that comes with the
  18.04.06 ISO without updating, as the installation works without issue
  using the included installer.

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