Disabling Nix substitutes (the “binary cache”)

I don’t have a reliable internet connection at the moment. Yet still I need to build some software which I’m working on using nix-build. This shouldn’t be an issue, because all buildInputs (dependencies of the the build, so to say) are already in my /nix/store. But, calling nix-build showed me this today:

warning: unable to download 'https://cache.nixos.org/j7vdysvh2ikm3ksrdd1gzhmm702wg0nq.narinfo': Couldn't resolve host name (6); retrying in 300 ms
warning: unable to download 'https://cache.nixos.org/j7vdysvh2ikm3ksrdd1gzhmm702wg0nq.narinfo': Couldn't resolve host name (6); retrying in 519 ms
warning: unable to download 'https://cache.nixos.org/j7vdysvh2ikm3ksrdd1gzhmm702wg0nq.narinfo': Couldn't resolve host name (6); retrying in 1127 ms
warning: unable to download 'https://cache.nixos.org/j7vdysvh2ikm3ksrdd1gzhmm702wg0nq.narinfo': Couldn't resolve host name (6); retrying in 2757 ms
warning: unable to download 'https://cache.nixos.org/j7vdysvh2ikm3ksrdd1gzhmm702wg0nq.narinfo': Couldn't resolve host name (6); retrying in 4724 ms
warning: unable to download 'https://cache.nixos.org/j7vdysvh2ikm3ksrdd1gzhmm702wg0nq.narinfo': Couldn't resolve host name (6); retrying in 9981 ms
warning: unable to download 'https://cache.nixos.org/j7vdysvh2ikm3ksrdd1gzhmm702wg0nq.narinfo': Couldn't resolve host name (6); retrying in 20990 ms
error: unable to download 'https://cache.nixos.org/j7vdysvh2ikm3ksrdd1gzhmm702wg0nq.narinfo': Couldn't resolve host name (6)

Not nice. It took me some time to find the option to tell nix to not attempt to download anything it could easily build locally. It’s nix-build --option substitute false.

Not --option binary-caches false, or --fallback or whatever. Let’s hope I remember this the next time I need it.