bbc107ef1e
Binary caches can now specify a priority in their nix-cache-info file. The binary cache substituter checks caches in order of priority. This is to ensure that fast, static caches like nixos.org/binary-cache are processed before slow, dynamic caches like hydra.nixos.org.
392 lines
13 KiB
XML
392 lines
13 KiB
XML
<refentry 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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xml:id="sec-nix-push">
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<refmeta>
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<refentrytitle>nix-push</refentrytitle>
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<manvolnum>1</manvolnum>
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<refmiscinfo class="source">Nix</refmiscinfo>
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<refmiscinfo class="version"><xi:include href="version.txt" parse="text"/></refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>nix-push</refname>
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<refpurpose>generate a binary cache</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>nix-push</command>
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<arg choice='plain'><option>--dest</option> <replaceable>dest-dir</replaceable></arg>
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<arg><option>--bzip2</option></arg>
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<arg><option>--force</option></arg>
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<arg><option>--link</option></arg>
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<arg><option>--manifest</option></arg>
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<arg><option>--manifest-path</option> <replaceable>filename</replaceable></arg>
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<arg><option>--url-prefix</option> <replaceable>url</replaceable></arg>
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<arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsection><title>Description</title>
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<para>The command <command>nix-push</command> produces a
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<emphasis>binary cache</emphasis>, a directory containing compressed
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Nix archives (NARs) plus some metadata of the closure of the specified
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store paths. This directory can then be made available through a web
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server to other Nix installations, allowing them to skip building from
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source and instead download binaries from the cache
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automatically.</para>
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<para><command>nix-push</command> performs the following actions.
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<orderedlist>
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<listitem><para>Each path in <replaceable>paths</replaceable> is
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built (using <link
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linkend='rsec-nix-store-realise'><command>nix-store
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--realise</command></link>).</para></listitem>
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<listitem><para>All paths in the closure of
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<replaceable>paths</replaceable> are determined (using
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<command>nix-store --query --requisites
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--include-outputs</command>). Note that since the
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<option>--include-outputs</option> flag is used, if
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<replaceable>paths</replaceable> includes a store derivation, you
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get a combined source/binary distribution (e.g., source tarballs
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will be included).</para></listitem>
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<listitem><para>All store paths determined in the previous step are
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packaged into a NAR (using <command>nix-store --dump</command>) and
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compressed using <command>xz</command> or <command>bzip2</command>.
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The resulting files have the extension <filename>.nar.xz</filename>
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or <filename>.nar.bz2</filename>. Also for each store path, Nix
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generates a file with extension <filename>.narinfo</filename>
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containing metadata such as the references, cryptographic hash and
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size of each path.</para></listitem>
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<listitem><para>Optionally, a single <emphasis>manifest</emphasis>
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file is created that contains the same metadata as the
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<filename>.narinfo</filename> files. This is for compatibility with
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Nix versions prior to 1.2 (see <command>nix-pull</command> for
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details).</para></listitem>
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<listitem><para>A file named <option>nix-cache-info</option> is
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placed in the destination directory. The existence of this file
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marks the directory as a binary cache.</para></listitem>
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</orderedlist>
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</para>
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</refsection>
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<refsection><title>Options</title>
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<variablelist>
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<varlistentry><term><option>--dest</option> <replaceable>dest-dir</replaceable></term>
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<listitem><para>Set the destination directory to
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<replaceable>dir</replaceable>, which is created if it does not
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exist. This flag is required.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--bzip2</option></term>
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<listitem><para>Compress NARs using <command>bzip2</command>
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instead of <command>xz -9</command>. The latter compresses about
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30% better on typical archives, decompresses about twice as fast,
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but compresses a lot slower and is not supported by Nix prior to
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version 1.2.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--force</option></term>
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<listitem><para>Overwrite <filename>.narinfo</filename> files if
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they already exist.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--link</option></term>
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<listitem><para>By default, NARs are generated in the Nix store
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and then copied to <replaceable>dest-dir</replaceable>. If this
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option is given, hard links are used instead. This only works if
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<replaceable>dest-dir</replaceable> is on the same filesystem as
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the Nix store.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--manifest</option></term>
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<listitem><para>Force the generation of a manifest suitable for
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use by <command>nix-pull</command>. The manifest is stored as
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<filename><replaceable>dest-dir</replaceable>/MANIFEST</filename>.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--manifest-path</option> <replaceable>filename</replaceable></term>
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<listitem><para>Like <option>--manifest</option>, but store the
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manifest in <replaceable>filename</replaceable>.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--url-prefix</option> <replaceable>url</replaceable></term>
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<listitem><para>Manifests are expected to contain the absolute
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URLs of NARs. For generating these URLs, the prefix
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<replaceable>url</replaceable> is used. It defaults to
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<uri>file://<replaceable>dest-dir</replaceable></uri>.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsection>
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<refsection><title>Examples</title>
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<para>To add the closure of Thunderbird to a binary cache:
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<screen>
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$ nix-push --dest /tmp/cache $(nix-build -A thunderbird)
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</screen>
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Assuming that <filename>/tmp/cache</filename> is exported by a web
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server as <uri>http://example.org/cache</uri>, you can then use this
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cache on another machine to speed up the installation of Thunderbird:
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<screen>
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$ nix-build -A thunderbird --option binary-caches http://example.org/cache
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</screen>
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Alternatively, you could add <literal>binary-caches =
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http://example.org/cache</literal> to
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<filename>nix.conf</filename>.</para>
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<para>To also include build-time dependencies (such as source
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tarballs):
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<screen>
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$ nix-push --dest /tmp/cache $(nix-instantiate -A thunderbird)
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</screen>
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</para>
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<para>To generate a manifest suitable for <command>nix-pull</command>:
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<screen>
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$ nix-push --dest /tmp/cache $(nix-build -A thunderbird) --manifest
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</screen>
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On another machine you can then do:
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<screen>
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$ nix-pull http://example.org/cache
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</screen>
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to cause the binaries to be used by subsequent Nix operations.</para>
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</refsection>
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<refsection><title>Binary cache format and operation</title>
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<para>A binary cache with URL <replaceable>url</replaceable> only
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denotes a valid binary cache if the file
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<uri><replaceable>url</replaceable>/nix-cache-info</uri> exists. If
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this file does not exist (or cannot be downloaded), the cache is
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ignored. If it does exist, it must be a text file containing cache
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properties. Here’s an example:
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<screen>
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StoreDir: /nix/store
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WantMassQuery: 1
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Priority: 10
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</screen>
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The properties that are currently supported are:
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<variablelist>
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<varlistentry><term><literal>StoreDir</literal></term>
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<listitem><para>The path of the Nix store to which this binary
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cache applies. Binaries are not relocatable — a binary built for
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<filename>/nix/store</filename> won’t generally work in
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<filename>/home/alice/store</filename> — so to prevent binaries
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from being used in a wrong store, a binary cache is only used if
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its <literal>StoreDir</literal> matches the local Nix
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configuration. The default is
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<filename>/nix/store</filename>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>WantMassQuery</literal></term>
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<listitem><para>Query operations such as <command>nix-env
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-qas</command> can cause thousands of cache queries, and thus
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thousands of HTTP requests, to determine which packages are
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available in binary form. While these requests are small, not
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every server may appreciate a potential onslaught of queries. If
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<literal>WantMassQuery</literal> is set to <literal>0</literal>
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(default), “mass queries” such as <command>nix-env -qas</command>
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will skip this cache. Thus a package may appear not to have a
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binary substitute. However, the binary will still be used when
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you actually install the package. If
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<literal>WantMassQuery</literal> is set to <literal>1</literal>,
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mass queries will use this cache.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>Priority</literal></term>
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<listitem><para>Each binary cache has a priority (defaulting to
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50). Binary caches are checked for binaries in order of ascending
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priority; thus a higher number denotes a lower priority. The
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binary cache <uri>http://nixos.org/binary-cache</uri> has priority
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40.</para></listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>Every time Nix needs to build some store path
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<replaceable>p</replaceable>, it will check each configured binary
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cache to see if it has a NAR file for <replaceable>p</replaceable>,
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until it finds one. If no cache has a NAR, Nix will fall back to
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building the path from source (if applicable). To see if a cache with
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URL <replaceable>url</replaceable> has a binary for
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<replaceable>p</replaceable>, Nix fetches
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<replaceable>url/h</replaceable>, where <replaceable>h</replaceable>
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is the hash part of <replaceable>p</replaceable>. Thus, if we have a
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cache <uri>http://nixos.org/binary-cache</uri> and we want to obtain
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the store path
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<screen>
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/nix/store/cj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13
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</screen>
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then Nix will attempt to fetch
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<screen>
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http://nixos.org/binary-cache/cj7a81wsm1ijwwpkks3725661h3263p5.narinfo
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</screen>
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(Commands such as <command>nix-env -qas</command> will issue an HTTP
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HEAD request, since it only needs to know if the
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<filename>.narinfo</filename> file exists.) The
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<filename>.narinfo</filename> file is a simple text file that looks
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like this:
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<screen>
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StorePath: /nix/store/cj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13
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URL: nar/0k6335lpbcmdgncqwkcry4dxr2m6qs77zia51684ynjgc7n5xx21.nar.bz2
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Compression: bzip2
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FileHash: sha256:0k6335lpbcmdgncqwkcry4dxr2m6qs77zia51684ynjgc7n5xx21
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FileSize: 10119014
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NarHash: sha256:120mhshkcgvn48xvxz0fjbd47k615v0viv7jy4gy7dwhmqapgd9d
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NarSize: 33702192
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References: cj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13 jfcs9xnfbmiwqs224sb0qqsybbfl3sab-linux-headers-2.6.35.14
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Deriver: xs32zzf2d58f6l5iz5fgwxrds2q5pnvn-glibc-2.13.drv
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System: x86_64-linux
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</screen>
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The fields are as follows:
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<variablelist>
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<varlistentry><term><literal>StorePath</literal></term>
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<listitem><para>The full store path, including the name part
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(e.g., <literal>glibc-2.13</literal>). It must match the
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requested store path.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>URL</literal></term>
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<listitem><para>The URL of the NAR, relative to the binary cache
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URL.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>Compression</literal></term>
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<listitem><para>The compression method; either
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<literal>xz</literal> or
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<literal>bzip2</literal>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>FileHash</literal></term>
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<listitem><para>The SHA-256 hash of the compressed
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NAR.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>FileSize</literal></term>
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<listitem><para>The size of the compressed NAR.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>NarHash</literal></term>
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<listitem><para>The SHA-256 hash of the uncompressed NAR. This is
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equal to the hash of the store path as returned by
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<command>nix-store -q --hash
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<replaceable>p</replaceable></command>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>NarSize</literal></term>
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<listitem><para>The size of the uncompressed NAR.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>References</literal></term>
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<listitem><para>The references of the store path, without the Nix
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store prefix.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>Deriver</literal></term>
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<listitem><para>The deriver of the store path, without the Nix
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store prefix. This field is optional.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>System</literal></term>
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<listitem><para>The Nix platform type of this binary, if known.
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This field is optional.</para></listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>Thus, in our example, after recursively ensuring that the
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references exist (e.g.,
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<filename>/nix/store/jfcs9xnfbmiwqs224sb0qqsybbfl3sab-linux-headers-2.6.35.14</filename>),
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Nix will fetch <screen>
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http://nixos.org/binary-cache/nar/0k6335lpbcmdgncqwkcry4dxr2m6qs77zia51684ynjgc7n5xx21.nar.bz2
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</screen> and decompress and unpack it to
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<filename>/nix/store/cj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13</filename>.</para>
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</refsection>
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</refentry>
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