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Before 24.04, there was a file /etc/apt/sources.list. With 24.04 the default file structure has changed.

  • Is there documentation about this change?
  • Does the old format still work or is only the new format valid?
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Support for the "new" DEB822 sources.list format was first added as far back as 2014, as noted in this changelog entry from Sun, 05 Jan 2014 15:13:32 +0100:

apt (0.9.14.3~exp1) experimental; urgency=low

  [ Michael Vogt ]   * add support for "deb822" style sources.list format and add
    APT::Sources::Use-Deb822 to support disabling it

The change to using the DEB822 format by default was proposed in Ubuntu discourse and actually implemented in Ubuntu 24.04, as documented in the Noble Numbat release notes:

deb822 sources management

The sources configuration for Ubuntu has moved from /etc/apt/sources.list to /etc/apt/sources.list.d/ubuntu.sources in the more featureful deb822 format, aligning with PPAs that already migrated to deb822 last year.

Both formats are described in the 24.04 sources.list manpage, where the entry for the older ONE-LINE-STYLE FORMAT confirms that it is supported "by all apt versions":

   This is the traditional format and supported by all apt versions. Note
   that not all options as described below are supported by all apt
   versions. Note also that some older applications parsing this format on
   their own might not expect to encounter options as they were uncommon
   before the introduction of multi-architecture support.
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  • As an addendum, the DEB822 format has been supported since APT version 1.1, released back in August of 2015. So the ‘new’ format has been supported for quite some time. It also has a number of advantages compared to the old format, so a number of third-party repos have been moving to it for a while now. Commented Jun 21 at 11:07
  • @AustinHemmelgarn thank you - I have trawled further back through the changelog and it seems to have first been added in 0.9.14.3~exp1 but then I see an entry " * bring back deb822 sources.list entries as .sources" in 1.1~exp9. Do you know if support was actually dropped in between these releases, or does the later entry just refer to a change in naming convention (.list versus .sources)? Commented Jun 22 at 16:29
  • I think they were originally looking at a hard migration without support for the original format, decided against that quickly, and then brought back the new format with a different file extension, but that’s mostly a guess based on the info in the changelogs. Almost everything I’ve seen suggests the first production version of APT that supported the new format is 1.1, so I don’t think it ever made it past development status before that. Commented Jun 22 at 20:09

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