730 lines
27 KiB
XML
730 lines
27 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-conf-file">
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<refmeta>
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<refentrytitle>nix.conf</refentrytitle>
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<manvolnum>5</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.conf</refname>
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<refpurpose>Nix configuration file</refpurpose>
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</refnamediv>
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<refsection><title>Description</title>
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<para>Nix reads settings from two configuration files:</para>
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<itemizedlist>
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<listitem>
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<para>The system-wide configuration file
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<filename><replaceable>sysconfdir</replaceable>/nix/nix.conf</filename>
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(i.e. <filename>/etc/nix/nix.conf</filename> on most systems), or
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<filename>$NIX_CONF_DIR/nix.conf</filename> if
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<envar>NIX_CONF_DIR</envar> is set.</para>
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</listitem>
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<listitem>
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<para>The user configuration file
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<filename>$XDG_CONFIG_HOME/nix/nix.conf</filename>, or
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<filename>~/.config/nix/nix.conf</filename> if
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<envar>XDG_CONFIG_HOME</envar> is not set.</para>
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</listitem>
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</itemizedlist>
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<para>The configuration files consist of
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<literal><replaceable>name</replaceable> =
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<replaceable>value</replaceable></literal> pairs, one per line.
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Comments start with a <literal>#</literal> character. Here is an
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example configuration file:</para>
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<programlisting>
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keep-outputs = true # Nice for developers
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keep-derivations = true # Idem
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</programlisting>
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<para>You can override settings on the command line using the
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<option>--option</option> flag, e.g. <literal>--option keep-outputs
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false</literal>.</para>
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<para>The following settings are currently available:
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<variablelist>
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<varlistentry xml:id="conf-keep-outputs"><term><literal>keep-outputs</literal></term>
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<listitem><para>If <literal>true</literal>, the garbage collector
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will keep the outputs of non-garbage derivations. If
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<literal>false</literal> (default), outputs will be deleted unless
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they are GC roots themselves (or reachable from other roots).</para>
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<para>In general, outputs must be registered as roots separately.
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However, even if the output of a derivation is registered as a
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root, the collector will still delete store paths that are used
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only at build time (e.g., the C compiler, or source tarballs
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downloaded from the network). To prevent it from doing so, set
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this option to <literal>true</literal>.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="conf-keep-derivations"><term><literal>keep-derivations</literal></term>
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<listitem><para>If <literal>true</literal> (default), the garbage
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collector will keep the derivations from which non-garbage store
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paths were built. If <literal>false</literal>, they will be
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deleted unless explicitly registered as a root (or reachable from
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other roots).</para>
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<para>Keeping derivation around is useful for querying and
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traceability (e.g., it allows you to ask with what dependencies or
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options a store path was built), so by default this option is on.
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Turn it off to save a bit of disk space (or a lot if
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<literal>keep-outputs</literal> is also turned on).</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>keep-env-derivations</literal></term>
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<listitem><para>If <literal>false</literal> (default), derivations
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are not stored in Nix user environments. That is, the derivation
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any build-time-only dependencies may be garbage-collected.</para>
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<para>If <literal>true</literal>, when you add a Nix derivation to
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a user environment, the path of the derivation is stored in the
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user environment. Thus, the derivation will not be
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garbage-collected until the user environment generation is deleted
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(<command>nix-env --delete-generations</command>). To prevent
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build-time-only dependencies from being collected, you should also
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turn on <literal>keep-outputs</literal>.</para>
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<para>The difference between this option and
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<literal>keep-derivations</literal> is that this one is
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“sticky”: it applies to any user environment created while this
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option was enabled, while <literal>keep-derivations</literal>
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only applies at the moment the garbage collector is
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run.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="conf-max-jobs"><term><literal>max-jobs</literal></term>
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<listitem><para>This option defines the maximum number of jobs
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that Nix will try to build in parallel. The default is
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<literal>1</literal>. The special value <literal>auto</literal>
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causes Nix to use the number of CPUs in your system. It can be
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overridden using the <option
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linkend='opt-max-jobs'>--max-jobs</option> (<option>-j</option>)
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command line switch.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="conf-cores"><term><literal>cores</literal></term>
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<listitem><para>Sets the value of the
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<envar>NIX_BUILD_CORES</envar> environment variable in the
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invocation of builders. Builders can use this variable at their
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discretion to control the maximum amount of parallelism. For
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instance, in Nixpkgs, if the derivation attribute
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<varname>enableParallelBuilding</varname> is set to
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<literal>true</literal>, the builder passes the
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<option>-j<replaceable>N</replaceable></option> flag to GNU Make.
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It can be overridden using the <option
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linkend='opt-cores'>--cores</option> command line switch and
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defaults to <literal>1</literal>. The value <literal>0</literal>
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means that the builder should use all available CPU cores in the
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system.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="conf-max-silent-time"><term><literal>max-silent-time</literal></term>
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<listitem>
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<para>This option defines the maximum number of seconds that a
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builder can go without producing any data on standard output or
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standard error. This is useful (for instance in an automated
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build system) to catch builds that are stuck in an infinite
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loop, or to catch remote builds that are hanging due to network
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problems. It can be overridden using the <option
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linkend="opt-max-silent-time">--max-silent-time</option> command
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line switch.</para>
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<para>The value <literal>0</literal> means that there is no
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timeout. This is also the default.</para>
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</listitem>
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</varlistentry>
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<varlistentry xml:id="conf-timeout"><term><literal>timeout</literal></term>
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<listitem>
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<para>This option defines the maximum number of seconds that a
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builder can run. This is useful (for instance in an automated
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build system) to catch builds that are stuck in an infinite loop
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but keep writing to their standard output or standard error. It
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can be overridden using the <option
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linkend="opt-timeout">--timeout</option> command line
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switch.</para>
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<para>The value <literal>0</literal> means that there is no
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timeout. This is also the default.</para>
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</listitem>
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</varlistentry>
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<varlistentry xml:id="conf-max-build-log-size"><term><literal>max-build-log-size</literal></term>
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<listitem>
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<para>This option defines the maximum number of bytes that a
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builder can write to its stdout/stderr. If the builder exceeds
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this limit, it’s killed. A value of <literal>0</literal> (the
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default) means that there is no limit.</para>
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</listitem>
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</varlistentry>
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<varlistentry xml:id="conf-build-users-group"><term><literal>build-users-group</literal></term>
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<listitem><para>This options specifies the Unix group containing
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the Nix build user accounts. In multi-user Nix installations,
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builds should not be performed by the Nix account since that would
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allow users to arbitrarily modify the Nix store and database by
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supplying specially crafted builders; and they cannot be performed
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by the calling user since that would allow him/her to influence
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the build result.</para>
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<para>Therefore, if this option is non-empty and specifies a valid
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group, builds will be performed under the user accounts that are a
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member of the group specified here (as listed in
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<filename>/etc/group</filename>). Those user accounts should not
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be used for any other purpose!</para>
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<para>Nix will never run two builds under the same user account at
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the same time. This is to prevent an obvious security hole: a
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malicious user writing a Nix expression that modifies the build
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result of a legitimate Nix expression being built by another user.
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Therefore it is good to have as many Nix build user accounts as
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you can spare. (Remember: uids are cheap.)</para>
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<para>The build users should have permission to create files in
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the Nix store, but not delete them. Therefore,
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<filename>/nix/store</filename> should be owned by the Nix
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account, its group should be the group specified here, and its
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mode should be <literal>1775</literal>.</para>
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<para>If the build users group is empty, builds will be performed
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under the uid of the Nix process (that is, the uid of the caller
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if <envar>NIX_REMOTE</envar> is empty, the uid under which the Nix
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daemon runs if <envar>NIX_REMOTE</envar> is
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<literal>daemon</literal>). Obviously, this should not be used in
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multi-user settings with untrusted users.</para>
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</listitem>
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</varlistentry>
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<varlistentry><term><literal>sandbox</literal></term>
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<listitem><para>If set to <literal>true</literal>, builds will be
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performed in a <emphasis>sandboxed environment</emphasis>, i.e.,
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they’re isolated from the normal file system hierarchy and will
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only see their dependencies in the Nix store, the temporary build
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directory, private versions of <filename>/proc</filename>,
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<filename>/dev</filename>, <filename>/dev/shm</filename> and
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<filename>/dev/pts</filename> (on Linux), and the paths configured with the
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<link linkend='conf-sandbox-paths'><literal>sandbox-paths</literal>
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option</link>. This is useful to prevent undeclared dependencies
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on files in directories such as <filename>/usr/bin</filename>. In
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addition, on Linux, builds run in private PID, mount, network, IPC
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and UTS namespaces to isolate them from other processes in the
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system (except that fixed-output derivations do not run in private
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network namespace to ensure they can access the network).</para>
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<para>Currently, sandboxing only work on Linux and macOS. The use
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of a sandbox requires that Nix is run as root (so you should use
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the <link linkend='conf-build-users-group'>“build users”
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feature</link> to perform the actual builds under different users
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than root).</para>
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<para>If this option is set to <literal>relaxed</literal>, then
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fixed-output derivations and derivations that have the
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<varname>__noChroot</varname> attribute set to
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<literal>true</literal> do not run in sandboxes.</para>
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<para>The default is <literal>false</literal>.</para>
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</listitem>
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</varlistentry>
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<varlistentry xml:id="conf-sandbox-paths">
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<term><literal>sandbox-paths</literal></term>
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<listitem><para>A list of paths bind-mounted into Nix sandbox
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environments. You can use the syntax
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<literal><replaceable>target</replaceable>=<replaceable>source</replaceable></literal>
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to mount a path in a different location in the sandbox; for
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instance, <literal>/bin=/nix-bin</literal> will mount the path
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<literal>/nix-bin</literal> as <literal>/bin</literal> inside the
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sandbox. If <replaceable>source</replaceable> is followed by
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<literal>?</literal>, then it is not an error if
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<replaceable>source</replaceable> does not exist; for example,
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<literal>/dev/nvidiactl?</literal> specifies that
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<filename>/dev/nvidiactl</filename> will only be mounted in the
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sandbox if it exists in the host filesystem.</para>
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<para>Depending on how Nix was built, the default value for this option
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may be empty or provide <filename>/bin/sh</filename> as a
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bind-mount of <command>bash</command>.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="conf-extra-sandbox-paths">
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<term><literal>build-extra-sandbox-paths</literal></term>
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<listitem><para>A list of additional paths appended to
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<option>sandbox-paths</option>. Useful if you want to extend
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its default value.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>substitute</literal></term>
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<listitem><para>If set to <literal>true</literal> (default), Nix
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will use binary substitutes if available. This option can be
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disabled to force building from source.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>fallback</literal></term>
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<listitem><para>If set to <literal>true</literal>, Nix will fall
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back to building from source if a binary substitute fails. This
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is equivalent to the <option>--fallback</option> flag. The
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default is <literal>false</literal>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>keep-build-log</literal></term>
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<listitem><para>If set to <literal>true</literal> (the default),
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Nix will write the build log of a derivation (i.e. the standard
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output and error of its builder) to the directory
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<filename>/nix/var/log/nix/drvs</filename>. The build log can be
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retrieved using the command <command>nix-store -l
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<replaceable>path</replaceable></command>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>compress-build-log</literal></term>
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<listitem><para>If set to <literal>true</literal> (the default),
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build logs written to <filename>/nix/var/log/nix/drvs</filename>
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will be compressed on the fly using bzip2. Otherwise, they will
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not be compressed.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>substituters</literal></term>
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<listitem><para>A list of URLs of substituters, separated by
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whitespace. The default is
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<literal>https://cache.nixos.org</literal>.</para></listitem>
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</varlistentry>
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<!--
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<varlistentry><term><literal>binary-caches-files</literal></term>
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<listitem><para>A list of names of files that will be read to
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obtain additional binary cache URLs. The default is
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<literal>/nix/var/nix/profiles/per-user/<replaceable>username</replaceable>/channels/binary-caches/*</literal>.
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Note that when you’re using the Nix daemon,
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<replaceable>username</replaceable> is always equal to
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<literal>root</literal>, so Nix will only use the binary caches
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provided by the channels installed by root. Do not set this
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option to read files created by untrusted users!</para></listitem>
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</varlistentry>
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-->
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<varlistentry><term><literal>trusted-substituters</literal></term>
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<listitem><para>A list of URLs of substituters, separated by
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whitespace. These are not used by default, but can be enabled by
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users of the Nix daemon by specifying <literal>--option
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substituters <replaceable>urls</replaceable></literal> on the
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command line. Unprivileged users are only allowed to pass a
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subset of the URLs listed in <literal>substituters</literal> and
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<literal>trusted-substituters</literal>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>extra-substituters</literal></term>
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<listitem><para>Additional binary caches appended to those
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specified in <option>substituters</option>. When used by
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unprivileged users, untrusted substituters (i.e. those not listed
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in <option>trusted-substituters</option>) are silently
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ignored.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>require-sigs</literal></term>
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<listitem><para>If set to <literal>true</literal> (the default),
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any non-content-addressed path added or copied to the Nix store
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(e.g. when substituting from a binary cache) must have a valid
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signature, that is, be signed using one of the keys listed in
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<option>trusted-public-keys</option> or
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<option>secret-key-files</option>. Set to <literal>false</literal>
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to disable signature checking.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>trusted-public-keys</literal></term>
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<listitem><para>A whitespace-separated list of public keys. When
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paths are copied from another Nix store (such as a binary cache),
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they must be signed with one of these keys. For example:
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<literal>cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
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hydra.nixos.org-1:CNHJZBh9K4tP3EKF6FkkgeVYsS3ohTl+oS0Qa8bezVs=</literal>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>secret-key-files</literal></term>
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<listitem><para>A whitespace-separated list of files containing
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secret (private) keys. These are used to sign locally-built
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paths. They can be generated using <command>nix-store
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--generate-binary-cache-key</command>. The corresponding public
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key can be distributed to other users, who can add it to
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<option>trusted-public-keys</option> in their
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<filename>nix.conf</filename>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>http-connections</literal></term>
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<listitem><para>The maximum number of parallel TCP connections
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used to fetch files from binary caches and by other downloads. It
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defaults to 25. 0 means no limit.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>netrc-file</literal></term>
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<listitem><para>If set to an absolute path to a <filename>netrc</filename>
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file, Nix will use the HTTP authentication credentials in this file when
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trying to download from a remote host through HTTP or HTTPS. Defaults to
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<filename>$NIX_CONF_DIR/netrc</filename>.</para>
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<para>The <filename>netrc</filename> file consists of a list of
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accounts in the following format:
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<screen>
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machine <replaceable>my-machine</replaceable>
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login <replaceable>my-username</replaceable>
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password <replaceable>my-password</replaceable>
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</screen>
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For the exact syntax, see <link
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xlink:href="https://ec.haxx.se/usingcurl-netrc.html">the
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<literal>curl</literal> documentation.</link></para></listitem>
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</varlistentry>
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<varlistentry><term><literal>system</literal></term>
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<listitem><para>This option specifies the canonical Nix system
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name of the current installation, such as
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<literal>i686-linux</literal> or
|
||
<literal>x86_64-darwin</literal>. Nix can only build derivations
|
||
whose <literal>system</literal> attribute equals the value
|
||
specified here. In general, it never makes sense to modify this
|
||
value from its default, since you can use it to ‘lie’ about the
|
||
platform you are building on (e.g., perform a Mac OS build on a
|
||
Linux machine; the result would obviously be wrong). It only
|
||
makes sense if the Nix binaries can run on multiple platforms,
|
||
e.g., ‘universal binaries’ that run on <literal>x86_64-linux</literal> and
|
||
<literal>i686-linux</literal>.</para>
|
||
|
||
<para>It defaults to the canonical Nix system name detected by
|
||
<filename>configure</filename> at build time.</para></listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry><term><literal>fsync-metadata</literal></term>
|
||
|
||
<listitem><para>If set to <literal>true</literal>, changes to the
|
||
Nix store metadata (in <filename>/nix/var/nix/db</filename>) are
|
||
synchronously flushed to disk. This improves robustness in case
|
||
of system crashes, but reduces performance. The default is
|
||
<literal>true</literal>.</para></listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry><term><literal>auto-optimise-store</literal></term>
|
||
|
||
<listitem><para>If set to <literal>true</literal>, Nix
|
||
automatically detects files in the store that have identical
|
||
contents, and replaces them with hard links to a single copy.
|
||
This saves disk space. If set to <literal>false</literal> (the
|
||
default), you can still run <command>nix-store
|
||
--optimise</command> to get rid of duplicate
|
||
files.</para></listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-connect-timeout"><term><literal>connect-timeout</literal></term>
|
||
|
||
<listitem>
|
||
|
||
<para>The timeout (in seconds) for establishing connections in
|
||
the binary cache substituter. It corresponds to
|
||
<command>curl</command>’s <option>--connect-timeout</option>
|
||
option.</para>
|
||
|
||
</listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-trusted-users"><term><literal>trusted-users</literal></term>
|
||
|
||
<listitem>
|
||
|
||
<para>A list of names of users (separated by whitespace) that
|
||
have additional rights when connecting to the Nix daemon, such
|
||
as the ability to specify additional binary caches, or to import
|
||
unsigned NARs. You can also specify groups by prefixing them
|
||
with <literal>@</literal>; for instance,
|
||
<literal>@wheel</literal> means all users in the
|
||
<literal>wheel</literal> group. The default is
|
||
<literal>root</literal>.</para>
|
||
|
||
<warning><para>Adding a user to <option>trusted-users</option>
|
||
is essentially equivalent to giving that user root access to the
|
||
system. For example, the user can set
|
||
<option>sandbox-paths</option> and thereby obtain read access to
|
||
directories that are otherwise inacessible to
|
||
them.</para></warning>
|
||
|
||
</listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-allowed-users"><term><literal>allowed-users</literal></term>
|
||
|
||
<listitem>
|
||
|
||
<para>A list of names of users (separated by whitespace) that
|
||
are allowed to connect to the Nix daemon. As with the
|
||
<option>trusted-users</option> option, you can specify groups by
|
||
prefixing them with <literal>@</literal>. Also, you can allow
|
||
all users by specifying <literal>*</literal>. The default is
|
||
<literal>*</literal>.</para>
|
||
|
||
<para>Note that trusted users are always allowed to connect.</para>
|
||
|
||
</listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-restrict-eval"><term><literal>restrict-eval</literal></term>
|
||
|
||
<listitem>
|
||
|
||
<para>If set to <literal>true</literal>, the Nix evaluator will
|
||
not allow access to any files outside of the Nix search path (as
|
||
set via the <envar>NIX_PATH</envar> environment variable or the
|
||
<option>-I</option> option), or to URIs outside of
|
||
<option>allowed-uri</option>. The default is
|
||
<literal>false</literal>.</para>
|
||
|
||
</listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-allowed-uris"><term><literal>allowed-uris</literal></term>
|
||
|
||
<listitem>
|
||
|
||
<para>A list of URI prefixes to which access is allowed in
|
||
restricted evaluation mode. For example, when set to
|
||
<literal>https://github.com/NixOS</literal>, builtin functions
|
||
such as <function>fetchGit</function> are allowed to access
|
||
<literal>https://github.com/NixOS/patchelf.git</literal>.</para>
|
||
|
||
</listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-pre-build-hook"><term><literal>pre-build-hook</literal></term>
|
||
|
||
<listitem>
|
||
|
||
|
||
<para>If set, the path to a program that can set extra
|
||
derivation-specific settings for this system. This is used for settings
|
||
that can't be captured by the derivation model itself and are too variable
|
||
between different versions of the same system to be hard-coded into nix.
|
||
</para>
|
||
|
||
<para>The hook is passed the derivation path and, if sandboxes are enabled,
|
||
the sandbox directory. It can then modify the sandbox and send a series of
|
||
commands to modify various settings to stdout. The currently recognized
|
||
commands are:</para>
|
||
|
||
<variablelist>
|
||
<varlistentry xml:id="extra-sandbox-paths">
|
||
<term><literal>extra-sandbox-paths</literal></term>
|
||
|
||
<listitem>
|
||
|
||
<para>Pass a list of files and directories to be included in the
|
||
sandbox for this build. One entry per line, terminated by an empty
|
||
line. Entries have the same format as
|
||
<literal>sandbox-paths</literal>.</para>
|
||
|
||
</listitem>
|
||
|
||
</varlistentry>
|
||
</variablelist>
|
||
</listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-repeat"><term><literal>repeat</literal></term>
|
||
|
||
<listitem><para>How many times to repeat builds to check whether
|
||
they are deterministic. The default value is 0. If the value is
|
||
non-zero, every build is repeated the specified number of
|
||
times. If the contents of any of the runs differs from the
|
||
previous ones, the build is rejected and the resulting store paths
|
||
are not registered as “valid” in Nix’s database.</para></listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-sandbox-dev-shm-size"><term><literal>sandbox-dev-shm-size</literal></term>
|
||
|
||
<listitem><para>This option determines the maximum size of the
|
||
<literal>tmpfs</literal> filesystem mounted on
|
||
<filename>/dev/shm</filename> in Linux sandboxes. For the format,
|
||
see the description of the <option>size</option> option of
|
||
<literal>tmpfs</literal> in
|
||
<citerefentry><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry>. The
|
||
default is <literal>50%</literal>.</para></listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-allow-import-from-derivation"><term><literal>allow-import-from-derivation</literal></term>
|
||
|
||
<listitem><para>By default, Nix allows you to <function>import</function> from a derivation,
|
||
allowing building at evaluation time. With this option set to false, Nix will throw an error
|
||
when evaluating an expression that uses this feature, allowing users to ensure their evaluation
|
||
will not require any builds to take place.</para></listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-allow-new-privileges"><term><literal>allow-new-privileges</literal></term>
|
||
|
||
<listitem><para>(Linux-specific.) By default, builders on Linux
|
||
cannot acquire new privileges by calling setuid/setgid programs or
|
||
programs that have file capabilities. For example, programs such
|
||
as <command>sudo</command> or <command>ping</command> will
|
||
fail. (Note that in sandbox builds, no such programs are available
|
||
unless you bind-mount them into the sandbox via the
|
||
<option>sandbox-paths</option> option.) You can allow the
|
||
use of such programs by enabling this option. This is impure and
|
||
usually undesirable, but may be useful in certain scenarios
|
||
(e.g. to spin up containers or set up userspace network interfaces
|
||
in tests).</para></listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
<varlistentry xml:id="conf-hashed-mirrors"><term><literal>hashed-mirrors</literal></term>
|
||
|
||
<listitem><para>A list of web servers used by
|
||
<function>builtins.fetchurl</function> to obtain files by
|
||
hash. The default is
|
||
<literal>http://tarballs.nixos.org/</literal>. Given a hash type
|
||
<replaceable>ht</replaceable> and a base-16 hash
|
||
<replaceable>h</replaceable>, Nix will try to download the file
|
||
from
|
||
<literal>hashed-mirror/<replaceable>ht</replaceable>/<replaceable>h</replaceable></literal>.
|
||
This allows files to be downloaded even if they have disappeared
|
||
from their original URI. For example, given the default mirror
|
||
<literal>http://tarballs.nixos.org/</literal>, when building the derivation
|
||
|
||
<programlisting>
|
||
builtins.fetchurl {
|
||
url = https://example.org/foo-1.2.3.tar.xz;
|
||
sha256 = "2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae";
|
||
}
|
||
</programlisting>
|
||
|
||
Nix will attempt to download this file from
|
||
<literal>http://tarballs.nixos.org/sha256/2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae</literal>
|
||
first. If it is not available there, if will try the original URI.</para></listitem>
|
||
|
||
</varlistentry>
|
||
|
||
|
||
</variablelist>
|
||
|
||
</para>
|
||
|
||
</refsection>
|
||
|
||
</refentry>
|