ELI5: What is an immutable OS, in practical terms?
ELI5: What is an immutable OS, in practical terms?
I've heard of immutable OS's like Fedora Silverblue. As far as I understand it, this means that "system files" are read-only, and that this is more secure.
What I struggle to understand is, what does that mean in practical terms? How does installing packages or configuring software work, if system files can't be changed?
Another thing I don't really understand is what the benefits as an end user? What kinds of things can I do (or can be done by malware or someone else) to my Arch system that couldn't be done on an immutable system? I get that there's a security benefit just in that malware can't change system files -- but that is achieved by proper permission management on traditional systems too.
And I understand the benefit of something declarative like NixOS or Guix, which are also immutable. But a lot of OS's seem to be immutable but not purely declarative. I'm struggling to understand why that's useful.
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It's not just about malware, but more about system stability and avoiding breaking your system by bad updates. Updates are atomic (all or nothing) Ideally if something goes wrong, the update isn't applied at all. If you manage to boot to a bad config, you can fix it by rebooting in to the previous known good config.
This is immensely valuable for appliance-type devices that aren't meant to be "administered" by end users, like the Steam-deck, set top boxes, even Android phones. For laptops / desktops I'm sure it has some value for people who want a stable base, with newer flatpak/AppImages for day to day use.
As for how updates and system packages are installed, I can't answer the specific technologies used, but I believe the principle is that an entirely new/complete filesystem "image" is created / layered on top. Then you reboot to the new image.