Ubuntu 25.10 problem upgrading to 26.04

I’ve just received the message from update manager that I can finally update to 26.04 but when I try to update I receive this error:

/usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeFetcherCore.py:178: Warning: W:Lo scaricamento è eseguito come root, ma non in una sandbox, poiché l’utente “_apt” non ha accesso al file “resolute.tar.gz.gpg”. - pkgAcquire::Run (13: Permesso negato)
result = fetcher.run()
autenticazione di «resolute.tar.gz» con «resolute.tar.gz.gpg»
estrazione di «resolute.tar.gz»

Sorry, the message is in italian but it simply say that _apt user has no grants to access that file.
i’ve of course do the usual apt update, apt full-upgrade. I’ve also tried apt clean.
I’ve disabled all third parties repositories. No luck
On another machine everything worked as expected

I’ve never experienced the error, but ensure you don’t have any holds, or disabled sources.

A search online for people experiencing it had disabled sources or hadn’t checked the output of commands like apt update you mention.

eg. Error prevents upgrade to pre-release

Alternatively the following maybe helpful having many other things I’d check too

https://askubuntu.com/questions/908800/what-does-this-apt-error-message-download-is-performed-unsandboxed-as-root

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Since I did have funny errors because of permissions, you might want to check the UMASK of the root user (should be 022), most probably in a sudo context, which can alter that mask. In my paranoia, I had set UMASK 027 in /etc/login.defs. There are also sudoers settings, which have a bearing on that.

Using:

echo 'APT::Sandbox::User "root";' | sudo tee -a /etc/apt/apt.conf.d/10sandbox

made the warning go away but now I receive:

Distribution data outdated
Please ensure all package updates are installed, and then try again.

Of course everything is updated and unused package removed

I’ve tried:
sudo apt-get install --only-upgrade distro-info-data update-manager-core -y
and I receive:

distro-info-data è già alla versione più recente (0.66).
update-manager-core è già alla versione più recente (1:25.10.1).

So these packages are already updated. lsb_release -a is correct:

No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 25.10
Release: 25.10
Codename: questing

Tried also:

sudo rm -rf /var/lib/apt/lists/*
sudo apt clean
sudo apt update
sudo do-release-upgrade

Same error

The only solution (for me) is to patch DistUpgradeController.py in ubuntu-release-upgrader-<version_created_by_do_release_upgrade> and then execute dist-upgrade.py using sudo su

Have you actually checked the permissions of said file? Because I don’t think root as the sandbox user is the intended use of said sandbox; usually root is the only user standing a chance to escape sandboxes, i.e. it’s rather trivial for root to escape a chroot, IIRC.

Of course, it can be a workaround; nobody actually expects the release upgrader to do anything malevolent like trying to escape a sandbox. But if APT had some yet unknown RCE vulnerability, giving the attacker root privileges would be a gift they’d gladly accept, I guess.

There is your issue I bet… as that detail shows an non-updated package

A quick CLI scan here shows results

 distro-info-data | 0.66           | questing          | source, all
 distro-info-data | 0.66ubuntu0.1  | questing-security | source, all
 distro-info-data | 0.66ubuntu0.2  | questing-updates  | source, all

where you’re not your 0.66 matches the initial ISO media, but NOT and updated system using -updates or -security. You should NOT have the first line of output on anything but a new install; as it’ll get upgraded by the higher-value packages from other repositories when upgrades are applied.

I’d check you’ve NOT disabled your sources; as your details match either problems that would show in sudo apt update (such as errors, warnings or just missing lines!) and thus subsequent commands are not actually updating packages.

This is the same problem discussed in link I provided earlier, ie.

You mention running

but do realize this command only updates software lists, but DOES NOT apply any upgrades to your system; it needs to be followed by an apt upgrade or better an apt full-upgrade command to apply the upgrades found by updating your software lists.

Your output shows you’ve not applied updates, either as you’ve disabled sources; or haven’t dealt with warnings/errors or any missing lines of output from the command like sudo apt update in my opinion, or just not run any apt upgrade type of command.

It wasn’t a problem of updates (and of course I did a apt upgrade) or permissions. The problem was in the script. The DistUpgradeFetcherCore python script wasn’t recognize the NEW version at all. fromVersion, fromDist and toDist variables were correct while toVersion was empty! Setting manually toDist variable make the script work correctly

Don’t ask me why but that was the problem.

I wouldn’t be so sure about that. It may just mean that is has to be explicitly set or the code will fall back on toVersion = max(availableVersions) or something like that. But I also don’t have the script in front of me.

But if it’s truly a bug in said script you should report it.

The behavior is expected if your distro-info-data package does not have the target release …

If you look at the distro-info-data package that was released to the security and updates pockets you will find:

distro-info-data (0.66ubuntu0.1) questing; urgency=medium

  [...]
  * Add Ubuntu 26.04 LTS "Resolute Raccoon" (LP: #2126961)

 -- Florent 'Skia' Jacquet <florent.jacquet@canonical.com>  Fri, 10 Oct 2025 10:43:53 +0100

There are plenty more updated packages in -security and -universe that might have essential changes that are relevant for the upgrade … just hacking around in the upgrade script will have made you bypass these possibly essential changes so I’d expect more issues further down the road on this machine …

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Well,

It was Ubuntu that was show me the update to 26.04. I didn’t it myself.. So I was expecting a no-problem update like the other machine were 25.10 was installed.

In any case except for a Nautilus graphic problem everything is working correctly and also the update went fine with no warnings or errors.

Had the same issue. I did all upgrades from 24.04, but for some reason my

/etc/apt/sources.list.d/ubuntu.sources

didn’t include questing-security questing-updates Suites

I added them manually:

Types: deb
URIs: http://archive.ubuntu.com/ubuntu
Suites: questing questing-security questing-updates
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg

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