.. _sec-nix-network-issues:

Network Problems
~~~~~~~~~~~~~~~~

Nix uses a so-called *binary cache* to optimise building a
package from source into downloading it as a pre-built binary. That is,
whenever a command like :command:`nixos-rebuild` needs a path in the
Nix store, Nix will try to download that path from the Internet rather than
build it from source. The default binary cache is
https://cache.nixos.org/. If this cache is unreachable, Nix
operations may take a long time due to HTTP connection timeouts. You can
disable the use of the binary cache by adding , e.g.
::

    # nixos-rebuild switch --option use-binary-caches false

If you have an alternative binary cache at your disposal, you can use it
instead:
::

    # nixos-rebuild switch --option binary-caches http://my-cache.example.org/