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diff --git a/nixos/doc/manual/development/building-nixos.chapter.md b/nixos/doc/manual/development/building-nixos.chapter.md new file mode 100644 index 00000000000..3310dee98f9 --- /dev/null +++ b/nixos/doc/manual/development/building-nixos.chapter.md @@ -0,0 +1,46 @@ +# Building a NixOS (Live) ISO {#sec-building-image} + +Default live installer configurations are available inside `nixos/modules/installer/cd-dvd`. +For building other system images, [nixos-generators] is a good place to start looking at. + +You have two options: + +- Use any of those default configurations as is +- Combine them with (any of) your host config(s) + +System images, such as the live installer ones, know how to enforce configuration settings +on wich they immediately depend in order to work correctly. + +However, if you are confident, you can opt to override those +enforced values with `mkForce`. + +[nixos-generators]: https://github.com/nix-community/nixos-generators + +## Practical Instructions {#sec-building-image-instructions} + +```ShellSession +$ git clone https://github.com/NixOS/nixpkgs.git +$ cd nixpkgs/nixos +$ nix-build -A config.system.build.isoImage -I nixos-config=modules/installer/cd-dvd/installation-cd-minimal.nix default.nix +``` + +To check the content of an ISO image, mount it like so: + +```ShellSession +# mount -o loop -t iso9660 ./result/iso/cd.iso /mnt/iso +``` + +## Technical Notes {#sec-building-image-tech-notes} + +The config value enforcement is implemented via `mkImageMediaOverride = mkOverride 60;` +and therefore primes over simple value assignments, but also yields to `mkForce`. + +This property allows image designers to implement in semantically correct ways those +configuration values upon which the correct functioning of the image depends. + +For example, the iso base image overrides those file systems which it needs at a minimum +for correct functioning, while the installer base image overrides the entire file system +layout because there can't be any other guarantees on a live medium than those given +by the live medium itself. The latter is especially true befor formatting the target +block device(s). On the other hand, the netboot iso only overrides its minimum dependencies +since netboot images are always made-to-target. |