not possible to upgrade from Xenial and jump over an unsupported release

This bug was fixed in the package ubuntu-release-upgrader - 1:17.10.4

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ubuntu-release-upgrader (1:17.10.4) artful; urgency=medium

  * Create demoted.cfg.xenial and DistUpgrade.cfg.xenial so that upgrades from
    Ubuntu 16.04 to Ubuntu 17.10 are supported. (LP: #1692092)

 -- Brian Murray <email address hidden> Fri, 19 May 2017 14:04:13 -0700

Hello Brian, or anyone else affected,

Accepted ubuntu-release-upgrader into zesty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/ubuntu-release-upgrader/1:17.04.8 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

I updated the meta-release-proposed file on the server to point at the dist-upgrader in zesty-proposed and then ran through the test from the test case. I had to modify the cached meta-release-proposed file (since the we are verifying an SRU in -proposed) on my system to verify the SRU but after that the test passed.

bdmurray@clean-xenial-amd64:~$ do-release-upgrade -p
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [836 B]
Get:2 Upgrade tool [1,265 kB]
Fetched 1,266 kB in 0s (0 B/s)
authenticate 'yakkety.tar.gz' against 'yakkety.tar.gz.gpg'
extracting 'yakkety.tar.gz'

[screen is terminating]
bdmurray@clean-xenial-amd64:~$ vi ~/.cache/update-manager-core/meta-release-proposed
bdmurray@clean-xenial-amd64:~$ do-release-upgrade -p
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [836 B]
Get:2 Upgrade tool [1,268 kB]
Fetched 1,269 kB in 0s (0 B/s)
authenticate 'zesty.tar.gz' against 'zesty.tar.gz.gpg'
extracting 'zesty.tar.gz'

Additionally, when using the zesty tarball I did not receive an error about the upgrade path being unsupported.

This bug was fixed in the package ubuntu-release-upgrader - 1:17.04.8

---------------
ubuntu-release-upgrader (1:17.04.8) zesty; urgency=medium

  * Create demoted.cfg.xenial and DistUpgrade.cfg.xenial so that upgrades from
    Ubuntu 16.04 to Ubuntu 17.04 are supported. (LP: #1692092)

 -- Brian Murray <email address hidden> Fri, 19 May 2017 10:31:43 -0700

The verification of the Stable Release Update for ubuntu-release-upgrader has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.