How do I upgrade from 14.04 LTS to 16.04.1 LTS?

This is an issue that has appeared before: 4 years ago when upgrading from 12.04 LTS (Precise Pangolin) to 14.04.1 LTS (Trusty Tahr):

• Why is "No new release found" when upgrading from a LTS to the next?

It looks like a similar issue exists for the upgrade from 14.04 LTS (Trusty Tahr) to 16.04.1 LTS (Xenial Xerus) with the relevant update log not yet updated. There is a choice of two reasonable solutions at the moment:

1. Wait a little until this document is updated and then upgrade as normal

2. Use the following syntax now:

   sudo do-release-upgrade --devel-release
   

Ubuntu documentation speaks on this option of using the --devel-release or -d option:

For further stability of a LTS release there is a slight change in behaviour if you are currently running a LTS version. LTS systems are only automatically considered for an upgrade to the next LTS via do-release-upgrade with the first point release. So for example 14.04 will only upgrade once 16.04.1 is released. If you want to update before, e.g. on a subset of machines to evaluate the LTS upgrade for your setup the same argument as an upgrade to a dev release has to be used via the -d switch.

And certainly at the moment this should be a safe course to take. When undertaken on my own Trusty system:

andrew@corinth:~$ sudo do-release-upgrade
[sudo] password for andrew: 
Checking for a new Ubuntu release
No new release found
andrew@corinth:~$ sudo do-release-upgrade --devel-release
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [198 B]                                           
Get:2 Upgrade tool [1,265 kB]                                                  
Fetched 1,265 kB in 0s (0 B/s)                                                 
authenticate 'xenial.tar.gz' against 'xenial.tar.gz.gpg' 
extracting 'xenial.tar.gz'
[...]

And the process rolls on installing Xenial by utlising this alternative file. A few hints at upcoming resolution of this issue:

1. A few enquiries in IRC (thanks @ThomasWard) indicate imminent fixing of the issue pending the fixing of any bugs in the upgrade path...
2. A personal email to myself from a developer has indicated that this should be fixed in the week commencing July 25th
3. A Launchpad bug and Feature Request filed on this issue has some interesting comments...

Crossed fingers for a resolution soon!!

Note: The update log altered on July 29th my time, so issue now resolved...

References:

• Ubuntu Help Docs: do-release-upgrade
• Bharath/Lord Noh: "No new release found" upgrading from 14.04LTS to 16.04.1 [Bug + Feature Request]

For me the solution was not -d but rather -p. Maybe this is helpful for some of you encountering this problem.

Edit to explain (from man do-release-upgrade):

-d, --devel-release
              Check if upgrading to the latest devel release is possible

-p, --proposed
              Try upgrading to the latest  release  using  the  upgrader  from
              Ubuntu-proposed

do-release-upgrade has several useful switches. Reviewing the man page is always a good idea.