failure attempting to initiate upgrade from xenial to zesty

[Robert Collins]

The docs https://wiki.ubuntu.com/ZestyZapus/ReleaseNotes#Upgrading_from_Ubuntu_16.10 say to use do-release-upgrade but:

$ sudo do-release-upgrade
Checking for a new Ubuntu release
No new release found.

Asking for a development version instead throws a traceback:

$ sudo do-release-upgrade -d
Checking for a new Ubuntu release
ERROR:root:parse failed for '/var/lib/update-manager/meta-release-lts-development'
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/MetaRelease.py", line 240, in parse
    while index_tag.step():
SystemError: E:Unable to parse package file (1)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/MetaRelease.py", line 372, in download
    self.parse()
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/MetaRelease.py", line 278, in parse
    self.METARELEASE_URI)
UpdateManager.Core.MetaRelease.MetaReleaseParseError: Unable to parse http://changelogs.ubuntu.com/meta-release-lts-development
Upgrades to the development release are only
available from the latest supported release.

Asking for a proposed version also finds no version.
$ sudo do-release-upgrade -p
Checking for a new Ubuntu release
No new release found.

[Brian Murray (brian-murray)]

The file /etc/update-manager/release-upgrades has "Prompt=lts" set, while if you want to upgrade to Zesty, not an LTS, you'll need to have "Prompt=normal".

The issue with failing to parse meta-release-lts-development has also been reported in bug 1723115.