From Wikitech

Your shell username will be used when logging into Toolforge and other Wikimedia VPS hosts using ssh. This name is typically shorter than a wiki username. It must start with a-z, and can only contain lowercase a-z, 0-9 and - characters.

  • The error message "There was either an authentication database error or you are not allowed to update your external account." indicates an invalid or in use shell username was provided (see T18524).