What is the format of the /etc/apt/sources.list file for Ubuntu?
As an example of the kind of information I am looking for, here is an explanation for Debian sources.list. However, the various sections, such as Distribution and Component, reference Debian releases; I am looking for Ubuntu specific information.
To more specifically answer the question about the format of sources.list, I suggest man 5 sources.list, which you can also view on the web as sources.list(5) [alt link], which is more detailed than Debian's SourcesList wiki article.
My specific inquiry related to how to specify multiple options, which is covered by sources.list(5) § The deb and deb-src types: options, which says they should be space-delimited, e.g.
deb [arch=amd64 signed-by=/usr/share/keyrings/some-repo.gpg] http://some.repo/apt dev main
This becomes more relevant with the recent apt-key deprecation that suggests using signed-by for all third-party repositories. This is coming soon: "apt-key(8) will last be available in Debian 11 [released 2021.08] and Ubuntu 22.04."
(The only Ubuntu-specific part should be the release and component names, which you can learn from the prior answer to this question.)
The format is exactly the same for Ubuntu.
You can get the Ubuntu distribution release names here. In sources.list use only the lowercased adjective part (precise, trusty, wily, etc.). Example:
deb http://archive.ubuntu.com/ubuntu/ trusty main restricted
The components can be main, restricted, universe and multiverse.
More info: What's the difference between multiverse, universe, restricted and main?
