50 lines
2 KiB
Markdown
50 lines
2 KiB
Markdown
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# pkgs.mkBinaryCache {#sec-pkgs-binary-cache}
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`pkgs.mkBinaryCache` is a function for creating Nix flat-file binary caches. Such a cache exists as a directory on disk, and can be used as a Nix substituter by passing `--substituter file:///path/to/cache` to Nix commands.
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Nix packages are most commonly shared between machines using [HTTP, SSH, or S3](https://nixos.org/manual/nix/stable/package-management/sharing-packages.html), but a flat-file binary cache can still be useful in some situations. For example, you can copy it directly to another machine, or make it available on a network file system. It can also be a convenient way to make some Nix packages available inside a container via bind-mounting.
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Note that this function is meant for advanced use-cases. The more idiomatic way to work with flat-file binary caches is via the [nix-copy-closure](https://nixos.org/manual/nix/stable/command-ref/nix-copy-closure.html) command. You may also want to consider [dockerTools](#sec-pkgs-dockerTools) for your containerization needs.
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## Example
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The following derivation will construct a flat-file binary cache containing the closure of `hello`.
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```nix
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mkBinaryCache {
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rootPaths = [hello];
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}
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```
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- `rootPaths` specifies a list of root derivations. The transitive closure of these derivations' outputs will be copied into the cache.
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Here's an example of building and using the cache.
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Build the cache on one machine, `host1`:
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```shellSession
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nix-build -E 'with import <nixpkgs> {}; mkBinaryCache { rootPaths = [hello]; }'
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```
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```shellSession
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/nix/store/cc0562q828rnjqjyfj23d5q162gb424g-binary-cache
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```
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Copy the resulting directory to the other machine, `host2`:
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```shellSession
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scp result host2:/tmp/hello-cache
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```
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Substitute the derivation using the flat-file binary cache on the other machine, `host2`:
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```shellSession
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nix-build -A hello '<nixpkgs>' \
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--option require-sigs false \
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--option trusted-substituters file:///tmp/hello-cache \
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--option substituters file:///tmp/hello-cache
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```
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```shellSession
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/nix/store/gl5a41azbpsadfkfmbilh9yk40dh5dl0-hello-2.12.1
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```
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