nix-on-debian.sh

install_nix() {
	# Getting a new .deb from upstream.
	# → https://hydra.nixos.org/job/nix/maintenance/deb_debian8x86_64
	local deb_name="nix_1.11.16-1_amd64.deb"
	local deb_location="$CONFIG_DIR/artifacts/nix/$deb_name"

	echo "Installing nix..."
	cat > ~/.curlrc <<-EOF
	silent = true
	EOF

	echo "[1/5] Preparing groups and users."
	nix_setup_build_users

	echo "[2/5] Installing package..."
	export DEBIAN_FRONTEND=noninteractive
	_ dpkg --unpack "$deb_location"
	_ apt-get --assume-yes update
	_ apt-get --assume-yes install -f
	_ apt-get --assume-yes install nix libcurl4-nss-dev

	echo "[3/5] Preparing nix for multiuser use..."
	_ mkdir -p /nix/store
	_ chown root.nixbld /nix/store
	_ chown root /nix
	_ mkdir -p -m 1777 /nix/var/nix/gcroots/per-user
	_ mkdir -p -m 1777 /nix/var/nix/profiles/per-user	
	_ systemctl enable nix-daemon.socket
	_ systemctl start nix-daemon

	echo "Adding nix-multiuser to profile.d"
	# Script to fix some issues with multi-user.
	# This should be fixed in the next release, upstream
	# See
	#  → https://gist.github.com/benley/e4a91e8425993e7d6668
	#  → https://github.com/NixOS/nix/pull/452
	_ touch /etc/profile.d/nix-multiuser.sh
	_ chmod +x /etc/profile.d/nix-multiuser.sh
	cat > /etc/profile.d/nix-multiuser.sh <<-'EOF'
	export NIXPKGS_CONFIG="/etc/nix/nixpkgs-config.nix"
	export NIX_OTHER_STORES="/run/nix/remote-stores/*/nix"
	export NIX_USER_PROFILE_DIR="/nix/var/nix/profiles/per-user/$USER"
	export NIX_PROFILES="/nix/var/nix/profiles/default $HOME/.nix-profile"
	export NIX_PATH="/nix/var/nix/profiles/per-user/root/channels"
	export PATH="$HOME/.nix-profile/bin:$HOME/.nix-profile/sbin:/nix/var/nix/profiles/default/bin:/nix/var/nix/profiles/default/sbin:$PATH"

	
	# Use the nix daemon for multi-user builds
	if [ "$USER" != root -o ! -w /nix/var/nix/db ]; then
		export NIX_REMOTE=daemon
	fi

	# Set up the per-user profile.
	mkdir -m 0755 -p "$NIX_USER_PROFILE_DIR"
	if test "$(stat --printf '%u' "$NIX_USER_PROFILE_DIR")" != "$(id -u)"; then
		echo "WARNING: bad ownership on $NIX_USER_PROFILE_DIR" >&2
	fi

	if [ -w "$HOME" ]; then
		# Set the default profile.
		if ! [ -L "$HOME/.nix-profile" ]; then
			if [ "$USER" != root ]; then
				ln -s "$NIX_USER_PROFILE_DIR/profile" "$HOME/.nix-profile"
			else
				# Root installs in the system-wide profile by default.
				ln -s /nix/var/nix/profiles/default "$HOME/.nix-profile"
			fi
		fi

		# Create the per-user garbage collector roots directory.
		NIX_USER_GCROOTS_DIR=/nix/var/nix/gcroots/per-user/$USER
		mkdir -m 0755 -p "$NIX_USER_GCROOTS_DIR"
		if test "$(stat --printf '%u' "$NIX_USER_GCROOTS_DIR")" != "$(id -u)"; then
			echo "WARNING: bad ownership on $NIX_USER_GCROOTS_DIR" >&2
		fi

		# Set up a default Nix expression from which to install stuff.
		if [ ! -e "$HOME/.nix-defexpr" -o -L "$HOME/.nix-defexpr" ]; then
			rm -f "$HOME/.nix-defexpr"
			mkdir "$HOME/.nix-defexpr"
			if [ "$USER" != root ]; then
				ln -s /nix/var/nix/profiles/per-user/root/channels "$HOME/.nix-defexpr/channels_root"
			fi
		fi

		# Subscribe the to the Nixpkgs channel by default.
		if [ ! -e "$HOME/.nix-channels" ]; then
			echo "http://nixos.org/channels/nixpkgs-unstable nixpkgs" > "$HOME/.nix-channels"
		fi

		# Append ~/.nix-defexpr/channels/nixpkgs to $NIX_PATH so that
		# <nixpkgs> paths work when the user has fetched the Nixpkgs
		# channel.
		export NIX_PATH="${NIX_PATH:+$NIX_PATH:}nixpkgs=$HOME/.nix-defexpr/channels/nixpkgs"
	fi

	EOF

	echo "[4/5] Setting up channels..."
	_ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
	_ nix-channel --update

	# 
	# There is a bad interaction with bash-completion and nix-shell ` <= 1.11.4 `.
	# The culprit is hard to pinpoint, but I'd tend to say that what nix was
	# doing shouldn't have caused such an issue.
	#
	# See: https://github.com/NixOS/nix/issues/976#issuecomment-239677601
	#
	# Ths issue can only be seen in *specific* conditions, which sadly, we hit
	# with deployment scripting.
	#
	echo "[5/5] Installing nix with nix..."
	_ nix-env -i nix
	_ which nix-env
}

nix_setup_build_users() {
	# ||: since it might already exist.
	_ groupadd -r nixbld || :
	for n in $(seq 1 10); do
		_ useradd -c "Nix build user $n" \
			-d /var/empty -g nixbld -G nixbld -M -N -r -s "$(which nologin)" \
			"nixbld$n" || :
	done
}