[Bug 2130273] Re: do-release-upgrade deletes sources.list format entries during update to 25.10

[wicky]

I’ve experienced a similar issue during the upgrade to Ubuntu 25.10 —
certain legacy sources.list entries were completely removed instead of
being migrated. It seems the upgrader script only preserves repositories
in the new deb822 format, which might explain why older .list files like
Mozilla’s get lost. Until this is patched, it’s best to back up your
repository files manually before running do-release-upgrade.

For anyone interested in testing or comparing update behaviors across systems,  https://e28game.net/ 
 offers some helpful performance-related insights that might be useful when troubleshooting similar issues.

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https://bugs.launchpad.net/bugs/2130273

Title:
  do-release-upgrade deletes sources.list format entries during update
  to 25.10

Status in ubuntu-release-upgrader package in Ubuntu:
  New

Bug description:
  To reproduce:
  1. On Ubuntu 25.04, add a repository in the old sources.list format (https://wiki.debian.org/SourcesList#sources.list_format). For example, I've added the Mozilla Firefox repo via following https://support.mozilla.org/en-US/kb/install-firefox-linux "For Debian Bookworm or older" instructions.
  2. Start upgrade process to 25.10 via do-release-upgrade. In the beginning of the process, the sources.list format repos will be moved into e.g. "mozilla.list.migrate", while the deb822 repos will be copied into e.g. "ubuntu.sources.distUpgrade" 
  3. Finish upgrade. All files with deb822 format will still be there, but mozilla.list will be gone entirely.

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