core26: apt update fails due to armhf being added to the architectures list on arm64 platforms

[IsaacJT]

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• I've verified that this bug isn't described by any existing issues.

Bug description

Building a core26 snap on an arm64 host running 26.04 can result in the behaviour shown in the logs when snapcraft tries to update the apt sources list.

This is due to armhf automatically being added as an architecture as per https://github.com/canonical/craft-archives/blob/1b6bf121b3756ef420e0e9991c1a69da278d8490/craft_archives/repo/apt_sources_manager.py#L46 and the recent move of the arm64 archives to archive.ubuntu.com (armhf packages were not added). Previously, both arm64 and armhf packages were available in one place on ports.ubuntu.com, but recent arm64 LXD images use the new URL.

Steps to reproduce

Build a core26 arm64 snap in a clean LXD environment with a recent image.

Environment

Running on an arm64 self-hosted GitHub runner using the snapcore/action-build action, which uses LXD to run the build.

snapcraft.yaml

Log output

:: 2026-07-07 09:22:09.425 Reading sources from '/etc/apt/sources.list.d/ubuntu.sources'.
:: 2026-07-07 09:22:09.425 Updating field 'Architectures' to 'arm64 armhf'
:: 2026-07-07 09:22:09.425 Updating source 'http://archive.ubuntu.com/ubuntu/'.
:: 2026-07-07 09:22:09.425 Updating source 'http://security.ubuntu.com/ubuntu/'.
:: 2026-07-07 09:22:09.425 Writing updated sources to '/etc/apt/sources.list.d/ubuntu.sources'.
:: 2026-07-07 09:22:09.425 Writing updated sources to '/etc/apt/sources.list.d/ubuntu.sources'.
:: 2026-07-07 09:22:09.425 Adding repository architecture: arm64
:: 2026-07-07 09:22:09.431 Refreshing repositories
...
:: 2026-07-07 09:22:20.233 :: Reading package lists...
:: 2026-07-07 09:22:20.251 :: E: Failed to fetch http://security.ubuntu.com/ubuntu/dists/resolute-security/main/binary-armhf/Packages  404  Not Found [IP: 91.189.91.95 80]
:: 2026-07-07 09:22:20.251 :: E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/resolute/main/binary-armhf/Packages  404  Not Found [IP: 185.125.190.94 80]
:: 2026-07-07 09:22:20.251 :: E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/resolute-updates/main/binary-armhf/Packages  404  Not Found [IP: 185.125.190.94 80]

[Asalle]

Hi @mr-cal
a release of an image is blocked by this issue. Do you have any ETA for fixing it so we can change our plan/communicate with the partner?
Many thanks for taking a look into this issue!

[mr-cal]

Hey @Asalle,

I've created an upstream issue in craft-archives (canonical/craft-archives#230). The earliest we'd be able to work on it would next pulse, starting July 20th. If it's more urgent, please message me or @steinbro on mattermost and we can figure out an escalation.

Would a workaround be sufficient? I think if you remove the package-repositories key from the snapcraft.yaml, the build would succeed when building on arm64. It would fail when cross-building from amd64 to arm64, but would this be enough to unblock you in the short-term?

[syncronize-issues-to-jira]

Thank you for reporting your feedback to us!

The internal ticket has been created: https://warthogs.atlassian.net/browse/SNAPCRAFT-1367.

This message was autogenerated

[IsaacJT]

Would a workaround be sufficient? I think if you remove the package-repositories key from the snapcraft.yaml, the build would succeed when building on arm64. It would fail when cross-building from amd64 to arm64, but would this be enough to unblock you in the short-term?

That would be acceptable for now - thanks for the suggestion. I'll see if it works.