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+# Release 1.2 (2012-12-06)
+
+This release has the following improvements and changes:
+
+  - Nix has a new binary substituter mechanism: the *binary cache*. A
+    binary cache contains pre-built binaries of Nix packages. Whenever
+    Nix wants to build a missing Nix store path, it will check a set of
+    binary caches to see if any of them has a pre-built binary of that
+    path. The configuration setting `binary-caches` contains a list of
+    URLs of binary caches. For instance, doing
+    
+        $ nix-env -i thunderbird --option binary-caches http://cache.nixos.org
+    
+    will install Thunderbird and its dependencies, using the available
+    pre-built binaries in <http://cache.nixos.org>. The main advantage
+    over the old “manifest”-based method of getting pre-built binaries
+    is that you don’t have to worry about your manifest being in sync
+    with the Nix expressions you’re installing from; i.e., you don’t
+    need to run `nix-pull` to update your manifest. It’s also more
+    scalable because you don’t need to redownload a giant manifest file
+    every time.
+    
+    A Nix channel can provide a binary cache URL that will be used
+    automatically if you subscribe to that channel. If you use the
+    Nixpkgs or NixOS channels (<http://nixos.org/channels>) you
+    automatically get the cache <http://cache.nixos.org>.
+    
+    Binary caches are created using `nix-push`. For details on the
+    operation and format of binary caches, see the `nix-push` manpage.
+    More details are provided in [this nix-dev
+    posting](https://nixos.org/nix-dev/2012-September/009826.html).
+
+  - Multiple output support should now be usable. A derivation can
+    declare that it wants to produce multiple store paths by saying
+    something like
+    
+        outputs = [ "lib" "headers" "doc" ];
+    
+    This will cause Nix to pass the intended store path of each output
+    to the builder through the environment variables `lib`, `headers`
+    and `doc`. Other packages can refer to a specific output by
+    referring to `pkg.output`, e.g.
+    
+        buildInputs = [ pkg.lib pkg.headers ];
+    
+    If you install a package with multiple outputs using `nix-env`, each
+    output path will be symlinked into the user environment.
+
+  - Dashes are now valid as part of identifiers and attribute names.
+
+  - The new operation `nix-store --repair-path` allows corrupted or
+    missing store paths to be repaired by redownloading them. `nix-store
+    --verify --check-contents
+                    --repair` will scan and repair all paths in the Nix store.
+    Similarly, `nix-env`, `nix-build`, `nix-instantiate` and `nix-store
+    --realise` have a `--repair` flag to detect and fix bad paths by
+    rebuilding or redownloading them.
+
+  - Nix no longer sets the immutable bit on files in the Nix store.
+    Instead, the recommended way to guard the Nix store against
+    accidental modification on Linux is to make it a read-only bind
+    mount, like this:
+    
+        $ mount --bind /nix/store /nix/store
+        $ mount -o remount,ro,bind /nix/store
+    
+    Nix will automatically make `/nix/store` writable as needed (using a
+    private mount namespace) to allow modifications.
+
+  - Store optimisation (replacing identical files in the store with hard
+    links) can now be done automatically every time a path is added to
+    the store. This is enabled by setting the configuration option
+    `auto-optimise-store` to `true` (disabled by default).
+
+  - Nix now supports `xz` compression for NARs in addition to `bzip2`.
+    It compresses about 30% better on typical archives and decompresses
+    about twice as fast.
+
+  - Basic Nix expression evaluation profiling: setting the environment
+    variable NIX\_COUNT\_CALLS to `1` will cause Nix to print how many
+    times each primop or function was executed.
+
+  - New primops: `concatLists`, `elem`, `elemAt` and `filter`.
+
+  - The command `nix-copy-closure` has a new flag `--use-substitutes`
+    (`-s`) to download missing paths on the target machine using the
+    substitute mechanism.
+
+  - The command `nix-worker` has been renamed to `nix-daemon`. Support
+    for running the Nix worker in “slave” mode has been removed.
+
+  - The `--help` flag of every Nix command now invokes `man`.
+
+  - Chroot builds are now supported on systemd machines.
+
+This release has contributions from Eelco Dolstra, Florian Friesdorf,
+Mats Erik Andersson and Shea Levy.