Title: Using nix download bandwidth limit feature

	Title: Using nix download bandwidth limit feature
	Author: Solène
	Date: 23 August 2022
	Tags: bandwidth nix linux
	Description: This is a guide explaining how to set up NixOS to use a
	development version of nix including a new change supporting download
	speed limit.

	# Introduction

	I submitted a change to the nix package manager last week, and it got
	merged! It's now possible to define a bandwidth speed limit in the
	nix.conf configuration file.

	Link to the GitHub pull request

	This kind of limit setting is very important for users who don't have a
	fast Internet access, this allows the service to download packages
	while keep the network usable meanwhile.

	Unfortunately, we need to wait for the next Nix version to be available
	to use it, fortunately it's easy to override a package settings to use
	the merge commit as a new version for nix.

	Let's see how to configure NixOS to use a newer Nix version from git.

	# Setup

	On NixOS, we will override the nix package attributes to change its
	version and the according checksum.

	We want the new option "download-speed" that takes a value for the
	kilobytes per second speed limit.

	```nix
	nix.extraOptions = ''
	download-speed = 800
	'';
	nixpkgs.overlays = [
	(self: super:
	{
	nix = super.nix.overrideDerivation (oldAttrs: {
	name = "nix-unstable";
	src = super.fetchFromGitHub {
	owner = "NixOS";
	repo = "nix";
	rev = "8d84634e26d6a09f9ca3fe71fcf9cba6e4a95107";
	sha256 = "sha256-Z6weLCmdPZR044PIAA4GRlkQRoyAc0s5ASeLr+eK1N0=…
	};
	});
	})
	];
	```

	Run "nixos-rebuild switch" as root, and voilà!

	For non-NixOS, you can clone the git repository, checkout the according
	commit, build nix and install it on your system.

	# Going further

	Don't forget to remove that override setting once a new nix release
	will be published, or you will keep an older version of nix.