nix (functional package manager)

Nix is a purely functional package manager. This means that it treats packages
like values in purely functional programming languages such as Haskell -- they
are built by functions that don't have side-effects, and they never change
after they have been built. Nix stores packages in the Nix store, usually the
directory /nix/store, where each package has its own unique subdirectory such
as

	/nix/store/b6gvzjyb2pg0kjfwrjmg1vfhh54ad73z-firefox-33.1/

where b6gvzjyb2pg0... is a unique identifier for the package that captures all
its dependencies (it's a cryptographic hash of the package's build dependency
graph).

Nix may be run in single or multi-user mode (which requires the nix-daemon). To
have the nix daemon start and stop with your host, add to /etc/rc.d/rc.local:

	if [ -x /etc/rc.d/rc.nix ]; then
		/etc/rc.d/rc.nix start
	fi

and to /etc/rc.d/rc.local_shutdown (creating it if needed):

	if [ -x /etc/rc.d/rc.nix ]; then
		/etc/rc.d/rc.nix stop
	fi

The daemon requires users for building the nix packages, which should be added
under the 'nixbld' group.

	groupadd -g 314 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

Restricting access to the daemon is acheived by setting file permissions for
the daemon's socket's folder.

	chgrp nix-users /nix/var/nix/daemon-socket
	chmod ug=rwx,o= /nix/var/nix/daemon-socket

Correct permissions must also be set for the following profile directories to give users access.

	/nix/var/nix/profiles
	/var/nix/profiles