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

According to Ubuntu Engineering Foundations team manager Steve Langasek:

Upgrades between LTS releases are not enabled by default until the first point release, 14.04.1, scheduled for July. It is recommended that most LTS users wait until then before upgrading to 14.04.

If you choose to upgrade before then, you can pass the -d option to the upgrade tool, running do-release-upgrade -d or update-manager -d, to upgrade from vanilla 12.04 to 14.04. (-d stands for devel.)

This question explains the justification for waiting for the prompt:

• Upgrading LTS to LTS (server) -- why wait for the first point release?

If one has no access to a GUI and wants the update on terminal:

1. Edit the file

   /etc/update-manager/release-upgrades
   

   for Prompt to match either normal or lts. (See list below what fits your case, be aware that you can only upgrade an LTS to another LTS version):

   [DEFAULT]
   Prompt=normal
   

2. Test correct version is found, run

   do-release-upgrade -c
   

3. Upgrade in case correct version is shown:

   sudo do-release-upgrade
   

   If you want to upgrade to development state (e.g. if you want to go from 18.10 to 19.04 before its official release) the -d flag is helpful:

   sudo do-release-upgrade -d
   

That way I could upgrade a 12.04 to 12.10.

The available Prompt options are:

• never - Never check for a new release.
• normal - Check to see if a new release is available. If more than one new release is found, the release upgrader will attempt to upgrade to the release that immediately succeeds the currently-running release.
• lts - Check to see if a new LTS release is available. The upgrader will attempt to upgrade to the first LTS release available after the currently-running one. Note that this option should not be used if the currently-running release is not itself an LTS release, since in that case the upgrader won't be able to determine if a newer release is available.

sudo do-release-upgrade -d 

Notice the -d at the end; from the man page:

  -d, --devel-release
      If using the latest supported release, upgrade to the development release

This works even with Prompt=lts in /etc/update-manager/release-upgrades.

In case you are having this issue and it's not the 18.04.1 problem or and switching to lts or non-lts updates changes nothing, try the following (super hard to find steps).

Open a terminal and type: export DEBUG_UPDATE_MANAGER=true before the do-release-upgrade -c command to see what goes wrong.

If you are getting the same problem I have you would see:

result of meta-release download: '<urlopen error timed out>'
NO self.metarelease_information
No new release found.

You could be facing the issue that you have a proxy configured for apt that is no longer relevant. Because of historic reasons (bug #446552), there are several unreasonable places where the updater will look for proxy settings. Beside the system-wide settings you should also check bash environment variables, gconf gnome proxy settings, /etc/apt/apt.conf and in my case /root/.synaptic/synaptic.conf.

The latter mind you no longer has a working menu in the GUI and the only way to remove the proxy settings is to edit the file. You can also just remove the file, that also works.

2 options :

1. Burn the iso and put it in your drive, it will detect the upgrade automatically

2. Go in you synaptics options, then Preference > distribution > Always prefer the highest version.

Problem solved ?