lix/doc/manual/src/package-management/binary-cache-substituter.md
Jan Tojnar ca4d8ce9e2 doc: De-emphasize nix-env without -A
The manual uses `nix-env -i` without `-A` prominently, teaching a bad practice to newcomers.
2021-11-17 17:04:25 +01:00

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# Serving a Nix store via HTTP
You can easily share the Nix store of a machine via HTTP. This allows
other machines to fetch store paths from that machine to speed up
installations. It uses the same *binary cache* mechanism that Nix
usually uses to fetch pre-built binaries from <https://cache.nixos.org>.
The daemon that handles binary cache requests via HTTP, `nix-serve`, is
not part of the Nix distribution, but you can install it from Nixpkgs:
```console
$ nix-env -iA nixpkgs.nix-serve
```
You can then start the server, listening for HTTP connections on
whatever port you like:
```console
$ nix-serve -p 8080
```
To check whether it works, try the following on the client:
```console
$ curl http://avalon:8080/nix-cache-info
```
which should print something like:
StoreDir: /nix/store
WantMassQuery: 1
Priority: 30
On the client side, you can tell Nix to use your binary cache using
`--option extra-binary-caches`, e.g.:
```console
$ nix-env -iA nixpkgs.firefox --option extra-binary-caches http://avalon:8080/
```
The option `extra-binary-caches` tells Nix to use this binary cache in
addition to your default caches, such as <https://cache.nixos.org>.
Thus, for any path in the closure of Firefox, Nix will first check if
the path is available on the server `avalon` or another binary caches.
If not, it will fall back to building from source.
You can also tell Nix to always use your binary cache by adding a line
to the `nix.conf` configuration file like this:
binary-caches = http://avalon:8080/ https://cache.nixos.org/