This is primarily a bug fix release. It also has a number of new features: nix-prefetch-url can now download URLs specified in a Nix expression. For example, $ nix-prefetch-url -A hello.src will prefetch the file specified by the fetchurl call in the attribute hello.src from the Nix expression in the current directory, and print the cryptographic hash of the resulting file on stdout. This differs from nix-build -A hello.src in that it doesn't verify the hash, and is thus useful when you’re updating a Nix expression. You can also prefetch the result of functions that unpack a tarball, such as fetchFromGitHub. For example: $ nix-prefetch-url --unpack https://github.com/NixOS/patchelf/archive/0.8.tar.gz or from a Nix expression: $ nix-prefetch-url -A nix-repl.src The builtin function <nix/fetchurl.nix> now supports downloading and unpacking NARs. This removes the need to have multiple downloads in the Nixpkgs stdenv bootstrap process (like a separate busybox binary for Linux, or curl/mkdir/sh/bzip2 for Darwin). Now all those files can be combined into a single NAR, optionally compressed using xz. Nix now supports SHA-512 hashes for verifying fixed-output derivations, and in builtins.hashString. The new flag --option build-repeat N will cause every build to be executed N+1 times. If the build output differs between any round, the build is rejected, and the output paths are not registered as valid. This is primarily useful to verify build determinism. (We already had a --check option to repeat a previously succeeded build. However, with --check, non-deterministic builds are registered in the DB. Preventing that is useful for Hydra to ensure that non-deterministic builds don't end up getting published to the binary cache.) Improved FreeBSD support. nix-env -qa --xml --meta now prints license information. The maximum number of parallel TCP connections that the binary cache substituter will use has been decreased from 150 to 25. This should prevent upsetting some broken NAT routers, and also improves performance. All "chroot"-containing strings got renamed to "sandbox". In particular, some Nix options got renamed, but the old names are still accepted as lower-priority aliases. This release has contributions from TODO.