I have Kubuntu 23.10. When I type:
sudo apt update && sudo apt upgrade -y && do-release-upgrade
I get:
Checking for a new Ubuntu release
There is no development version of an LTS available.
To upgrade to the latest non-LTS development release
set Prompt=normal in /etc/update-manager/release-upgrades.
Changing to normal in the file above also does nothing.
What's going on?
The upgrade path is not open due to BLOCKER bugs.
For update in September 2024 - skip to near end
Refer to https://discourse.ubuntu.com/t/noble-numbat-24-04-release-status-tracking/44043 for the current status, and especially note the "Current blockers for enabling upgrades from Mantic" section for BLOCKER bugs for mantic (23.10) to noble (24.04).
Ubuntu 24.04 LTS is currently available for new installs, which is the purpose of the ISO release.
The do-release-upgrade command will check what upgrades are available; which it does by reading https://changelogs.ubuntu.com/meta-release where you'll note no mention of Ubuntu 24.04 LTS, as it's not currently supported for release-upgrades.
Forcing Upgrade
You can force upgrade using the -d option, which will cause this file (https://changelogs.ubuntu.com/meta-release-development) to be used instead, thus it will be seen, but that is available mostly for QA or Quality Assurance testing, and will remain that until the BLOCKER bugs have been dealt with. The upgrade will be opened when the Ubuntu Release team deem the upgrade to be stable.
The official upgrade documentation can be read at https://help.ubuntu.com/community/NobleUpgrades where you'll note -d is mentioned.
Additional notes
It's normal for a release to not be opened until the following week after release (releases are always a Thursday), and for LTS releases, that upgrade can sometimes open a week or two later too. The LTS to LTS release is the same, except the 22.04 LTS won't be examined until after release of Ubuntu 24.04.1 LTS.
Also please note Kubuntu is the same as Ubuntu here, with all release-upgrades using the same code with upgrades for all (inc. flavors like Kubuntu) managed by the Ubuntu Release team.
Update on 24.04.1 Tracking
See https://discourse.ubuntu.com/t/noble-numbat-24-04-1-lts-point-release-status-tracking/46972 for tracking status of the 22.04.1 release, and take particular attention of the "Upgrade blockers" section.
You'll also note on that page that the planned date of 15-August-2024 has been pushed back to 29-August-2024.
The path of upgrades from 22.04 to 24.04 was opened after release of 24.04.1, but it was soon recognized some users were experiencing problems and thus the 'taps" were paused (see here)
Utkarsh Gupta (of the Ubuntu Release team) has provided 'public notice' which reads
We’ve discovered a bug in ubuntu-release-upgrader in the code that enables a new apt algorithm to handle obsolete packages.
Therefore, updates to Noble have been temporarily suspended while the issue is being addressed.
The fixes are in the pipeline already and we should be re-enabling the upgrades soon. Once done, expect to hear from us along with the retrospective on what happened and what we are doing to ensure that this doesn’t happen again.
https://discourse.ubuntu.com/t/upgrades-to-ubuntu-24-04-1-lts-are-enabled-again/47920
Julian Andres Klode gives a brief summary on suspension & tells us the issue has been resolved and upgrades are back open. The reason for suspension is outlined, plus for any systems that were 'broken' by this issue, a simple apt install --fix-broken should resolve issues.
See: https://kubuntu.org/news/kubuntu-24-04-lts-noble-numbat-released/
Note: For upgrades from 23.10, there may a delay of a few hours to days between the official release announcements and the Ubuntu Release Team enabling upgrades.
Upgrading manually worked in my case:
sudo sed -i 's/mantic/noble/g' /etc/apt/sources.list && sudo apt-get upgrade && sudo apt-get dist-upgrade && sudo apt-get autoremove && sudo apt-get clean && sudo reboot
Something was messed up in sources.list and do-release-upgrade couldn't fix it.