nix-super/src/nix/make-content-addressed.md

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Examples

• Create a content-addressed representation of the closure of GNU Hello:

  # nix store make-content-addressed nixpkgs#hello
  …
  rewrote '/nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10' to '/nix/store/5skmmcb9svys5lj3kbsrjg7vf2irid63-hello-2.10'
  

  Since the resulting paths are content-addressed, they are always trusted and don't need signatures to copied to another store:

  # nix copy --to /tmp/nix --trusted-public-keys '' /nix/store/5skmmcb9svys5lj3kbsrjg7vf2irid63-hello-2.10
  

  By contrast, the original closure is input-addressed, so it does need signatures to be trusted:

  # nix copy --to /tmp/nix --trusted-public-keys '' nixpkgs#hello
  cannot add path '/nix/store/zy9wbxwcygrwnh8n2w9qbbcr6zk87m26-libunistring-0.9.10' because it lacks a signature by a trusted key
  

• Create a content-addressed representation of the current NixOS system closure:

  # nix store make-content-addressed /run/current-system
  

Description

This command converts the closure of the store paths specified by installables to content-addressed form. Nix store paths are usually input-addressed, meaning that the hash part of the store path is computed from the contents of the derivation (i.e., the build-time dependency graph). Input-addressed paths need to be signed by a trusted key if you want to import them into a store, because we need to trust that the contents of the path were actually built by the derivation.

By contrast, in a content-addressed path, the hash part is computed from the contents of the path. This allows the contents of the path to be verified without any additional information such as signatures. This means that a command like

# nix store build /nix/store/5skmmcb9svys5lj3kbsrjg7vf2irid63-hello-2.10 \
    --substituters https://my-cache.example.org

will succeed even if the binary cache https://my-cache.example.org doesn't present any signatures.

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