Upgrade Ubuntu 25.10 -> 26.04 LTS | Bug "Distribution data outdated"

A do-release-upgrade from Ubuntu 25.10 to 26.04 LTS may fail because the system considers the target distribution invalid. The error message "Distribution data outdated" appears even though the system has been fully updated through the standard package repositories.

The technical root cause lies within the validation logic of Canonical's upgrade tool. The Python script compares the target codename against a local database provided by the distro-info-data package.

Because version 0.66 available in the Ubuntu 25.10 (Questing Quokka) repositories does not yet contain the codename for Ubuntu 26.04 (Resolute Raccoon), the tool strictly refuses to proceed. The system protects itself from what it considers an undefined upgrade path.

To unlock the upgrade process, the metadata database must be manually updated by installing version 0.69.

Before performing deep modifications to the release structure, the current package tree must be completely consistent. Package manager inconsistencies (dpkg) or unresolved dependencies will inevitably cause failures during the operating system upgrade and may leave the system unbootable.

First synchronize package indexes and perform a complete system upgrade. The full-upgrade parameter is essential because, unlike a standard upgrade, it is allowed to resolve package conflicts by removing obsolete or blocking packages. Running autoremove afterward cleans up orphaned libraries that could otherwise interfere with the upgrade process.

A reboot ensures that no outdated kernel modules remain loaded in memory.

Because version 0.69 of distro-info-data is available on Canonical's master servers but has not yet been published through the regular Ubuntu 25.10 update channel, you must bypass APT.

Download the Debian package directly from Canonical's package pool. Since this is an architecture-independent package (_all.deb) containing only CSV metadata and no compiled binaries, the manual installation is considered safe.

Download the package using wget and install it through dpkg.

The do-release-upgrade utility downloads a compressed archive containing release-specific Python upgrade routines, extracts them into /tmp, and executes them from there.

On hardened systems, especially those following CIS benchmarks, /tmp is commonly mounted with the noexec flag to prevent malware execution.

Unfortunately, this security control also blocks Canonical's upgrade scripts.

Temporarily remount /tmp with execution permissions enabled:

This modification exists only in memory and does not survive a reboot.

During package retrieval, APT drops privileges and operates as the _apt user. Restrictive file permissions, custom UMASK settings, or GPG key configuration issues can prevent _apt from accessing required resources.

If do-release-upgrade explicitly fails with _apt permission errors, temporarily disable the sandbox.

At this point the system should recognize Ubuntu 26.04 LTS as a valid target release.

When executed over SSH, the upgrade utility automatically creates an internal screen session, typically listening through TCP port 1022.

If the SSH connection is interrupted, the upgrade continues safely in the background.

Reconnect using:

Once the migration has completed, the system reboots into the Ubuntu 26.04 kernel.

Verify the installed release:

Systems relying on proprietary kernel modules such as NVIDIA drivers or specialized network adapters use Dynamic Kernel Module Support (DKMS).

DKMS automatically rebuilds modules against the new kernel. If the process fails due to timeouts or missing dependencies, the system may fall back to open-source alternatives such as Nouveau, potentially breaking CUDA workloads.

Force a manual rebuild:

Docker injects IPTables or NFTables rules directly into the host networking stack.

Since Ubuntu 26.04 updates firewall-related libraries, Docker bridge networks frequently lose connectivity after the upgrade.

Review running containers and restart the Docker daemon:

Finally, remove the temporary APT sandbox override:

The failure of do-release-upgrade when upgrading from Ubuntu 25.10 to Ubuntu 26.04 LTS highlights a significant release management issue. The fact that Ubuntu's primary migration tool can fail because of an outdated CSV metadata file that is not updated through normal APT channels is problematic, especially in enterprise environments.

Administrators are forced to bypass standard package management workflows and manually inject .deb packages through wget and dpkg. In automated infrastructures managed through Infrastructure-as-Code platforms such as Ansible or Puppet, this can lead to widespread deployment failures unless playbooks are updated accordingly.

The workaround also demonstrates the importance of understanding the underlying Linux architecture. Modifying /tmp mount flags from noexec to exec illustrates how deeply integrated upgrade mechanisms often depend on permissions intentionally restricted on hardened systems.

Likewise, temporarily disabling the APT sandbox highlights the operational tension between security controls and system maintenance. Security mechanisms designed to protect against compromised repositories can become obstacles during major operating system migrations.

Knowing the do-release-upgrade command alone is not enough. Administrators must understand mount options, privilege separation, package management internals, and DKMS kernel module compilation to reliably return a system to a secure and production-ready state after a major release upgrade.

Removing temporary sandbox overrides after the upgrade is a mandatory final step to restore the original security posture and avoid leaving the system exposed to unnecessary risk.