158 lines
5.9 KiB
XML
158 lines
5.9 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id="ssec-relnotes-1.2">
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<title>Release 1.2 (2012-12-06)</title>
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<para>This release has the following improvements and changes:</para>
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<itemizedlist>
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<listitem>
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<para>Nix has a new binary substituter mechanism: the
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<emphasis>binary cache</emphasis>. A binary cache contains
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pre-built binaries of Nix packages. Whenever Nix wants to build a
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missing Nix store path, it will check a set of binary caches to
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see if any of them has a pre-built binary of that path. The
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configuration setting <option>binary-caches</option> contains a
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list of URLs of binary caches. For instance, doing
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<screen>
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$ nix-env -i thunderbird --option binary-caches http://cache.nixos.org
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</screen>
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will install Thunderbird and its dependencies, using the available
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pre-built binaries in <uri>http://cache.nixos.org</uri>.
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The main advantage over the old “manifest”-based method of getting
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pre-built binaries is that you don’t have to worry about your
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manifest being in sync with the Nix expressions you’re installing
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from; i.e., you don’t need to run <command>nix-pull</command> to
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update your manifest. It’s also more scalable because you don’t
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need to redownload a giant manifest file every time.
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</para>
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<para>A Nix channel can provide a binary cache URL that will be
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used automatically if you subscribe to that channel. If you use
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the Nixpkgs or NixOS channels
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(<uri>http://nixos.org/channels</uri>) you automatically get the
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cache <uri>http://cache.nixos.org</uri>.</para>
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<para>Binary caches are created using <command>nix-push</command>.
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For details on the operation and format of binary caches, see the
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<command>nix-push</command> manpage. More details are provided in
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<link xlink:href="http://lists.science.uu.nl/pipermail/nix-dev/2012-September/009826.html">this
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nix-dev posting</link>.</para>
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</listitem>
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<listitem>
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<para>Multiple output support should now be usable. A derivation
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can declare that it wants to produce multiple store paths by
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saying something like
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<programlisting>
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outputs = [ "lib" "headers" "doc" ];
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</programlisting>
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This will cause Nix to pass the intended store path of each output
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to the builder through the environment variables
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<literal>lib</literal>, <literal>headers</literal> and
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<literal>doc</literal>. Other packages can refer to a specific
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output by referring to
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<literal><replaceable>pkg</replaceable>.<replaceable>output</replaceable></literal>,
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e.g.
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<programlisting>
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buildInputs = [ pkg.lib pkg.headers ];
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</programlisting>
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If you install a package with multiple outputs using
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<command>nix-env</command>, each output path will be symlinked
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into the user environment.</para>
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</listitem>
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<listitem>
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<para>Dashes are now valid as part of identifiers and attribute
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names.</para>
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</listitem>
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<listitem>
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<para>The new operation <command>nix-store --repair-path</command>
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allows corrupted or missing store paths to be repaired by
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redownloading them. <command>nix-store --verify --check-contents
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--repair</command> will scan and repair all paths in the Nix
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store. Similarly, <command>nix-env</command>,
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<command>nix-build</command>, <command>nix-instantiate</command>
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and <command>nix-store --realise</command> have a
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<option>--repair</option> flag to detect and fix bad paths by
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rebuilding or redownloading them.</para>
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</listitem>
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<listitem>
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<para>Nix no longer sets the immutable bit on files in the Nix
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store. Instead, the recommended way to guard the Nix store
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against accidental modification on Linux is to make it a read-only
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bind mount, like this:
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<screen>
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$ mount --bind /nix/store /nix/store
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$ mount -o remount,ro,bind /nix/store
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</screen>
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Nix will automatically make <filename>/nix/store</filename>
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writable as needed (using a private mount namespace) to allow
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modifications.</para>
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</listitem>
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<listitem>
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<para>Store optimisation (replacing identical files in the store
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with hard links) can now be done automatically every time a path
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is added to the store. This is enabled by setting the
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configuration option <literal>auto-optimise-store</literal> to
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<literal>true</literal> (disabled by default).</para>
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</listitem>
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<listitem>
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<para>Nix now supports <command>xz</command> compression for NARs
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in addition to <command>bzip2</command>. It compresses about 30%
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better on typical archives and decompresses about twice as
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fast.</para>
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</listitem>
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<listitem>
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<para>Basic Nix expression evaluation profiling: setting the
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environment variable <envar>NIX_COUNT_CALLS</envar> to
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<literal>1</literal> will cause Nix to print how many times each
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primop or function was executed.</para>
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</listitem>
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<listitem>
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<para>New primops: <varname>concatLists</varname>,
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<varname>elem</varname>, <varname>elemAt</varname> and
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<varname>filter</varname>.</para>
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</listitem>
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<listitem>
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<para>The command <command>nix-copy-closure</command> has a new
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flag <option>--use-substitutes</option> (<option>-s</option>) to
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download missing paths on the target machine using the substitute
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mechanism.</para>
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</listitem>
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<listitem>
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<para>The command <command>nix-worker</command> has been renamed
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to <command>nix-daemon</command>. Support for running the Nix
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worker in “slave” mode has been removed.</para>
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</listitem>
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<listitem>
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<para>The <option>--help</option> flag of every Nix command now
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invokes <command>man</command>.</para>
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</listitem>
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<listitem>
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<para>Chroot builds are now supported on systemd machines.</para>
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</listitem>
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</itemizedlist>
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<para>This release has contributions from Eelco Dolstra, Florian
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Friesdorf, Mats Erik Andersson and Shea Levy.</para>
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</section>
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