Nix 1.0 (2012-05-11) - Lix Reference Manual

## Keyboard shortcuts

Press `←` or `→` to navigate between chapters

Press `S` or `/` to search in the book

Press `?` to show this help

Press `Esc` to hide this help

# Release 1.0 (2012-05-11)

There have been numerous improvements and bug fixes since the previous release. Here are the most significant:

- Nix can now optionally use the Boehm garbage collector. This significantly reduces the Nix evaluator’s memory footprint, especially when evaluating large NixOS system configurations. It can be enabled using the `--enable-gc` configure option.

- Nix now uses SQLite for its database. This is faster and more flexible than the old ad hoc format. SQLite is also used to cache the manifests in `/nix/var/nix/manifests`, resulting in a significant speedup.

- Nix now has an search path for expressions. The search path is set using the environment variable `NIX_PATH` and the `-I` command line option. In Nix expressions, paths between angle brackets are used to specify files that must be looked up in the search path. For instance, the expression `<nixpkgs/default.nix>` looks for a file `nixpkgs/default.nix` relative to every element in the search path.

- The new command `nix-build --run-env` builds all dependencies of a derivation, then starts a shell in an environment containing all variables from the derivation. This is useful for reproducing the environment of a derivation for development.

- The new command `nix-store --verify-path` verifies that the contents of a store path have not changed.

- The new command `nix-store --print-env` prints out the environment of a derivation in a format that can be evaluated by a shell.

- Attribute names can now be arbitrary strings. For instance, you can write `{ "foo-1.2" = …; "bla bla" = …; }."bla bla"`.

- Attribute selection can now provide a default value using the `or` operator. For instance, the expression `x.y.z or e` evaluates to the attribute `x.y.z` if it exists, and `e` otherwise.

- The right-hand side of the `?` operator can now be an attribute path, e.g., `attrs ? a.b.c`.

- On Linux, Nix will now make files in the Nix store immutable on filesystems that support it. This prevents accidental modification of files in the store by the root user.

- Nix has preliminary support for derivations with multiple outputs. This is useful because it allows parts of a package to be deployed and garbage-collected separately. For instance, development parts of a package such as header files or static libraries would typically not be part of the closure of an application, resulting in reduced disk usage and installation time.

- The Nix store garbage collector is faster and holds the global lock for a shorter amount of time.

- The option `--timeout` (corresponding to the configuration setting `build-timeout`) allows you to set an absolute timeout on builds — if a build runs for more than the given number of seconds, it is terminated. This is useful for recovering automatically from builds that are stuck in an infinite loop but keep producing output, and for which `--max-silent-time` is ineffective.

- Nix development has moved to GitHub (https://github.com/NixOS/nix).