@iona nixos allows you to write a configuration file that defines your entire operating system: which programs are on it, how the filesystem works, what Desktop Environment you use, all of the settings for everything (basically)
this file is then used to *generate* a read-only OS, which is garunteed to be reproducable
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@iona if I write a nixos config file for my computer, then give it to you, and you write "nixos switch" to switch to that config, your OS will be *exactly* the same as mine (except for files in your home folder)
On top of this, any update to any part of your computer can be safely rolled back if it breaks something or if you just don't like it
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@iona
the main disadvantages are that you *have* to write this config file, and that all programs *have* to be installed the nixos way, rather than the "standard" linux way