522ecab9b8
AFAIK nobody uses this, setuid binaries are evil, and there is no good reason why people can't just run the daemon.
428 lines
17 KiB
XML
428 lines
17 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>A number of persistent settings of Nix are stored in the file
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<filename><replaceable>sysconfdir</replaceable>/nix/nix.conf</filename>.
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This file is a list of <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 example
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configuration file:</para>
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<programlisting>
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gc-keep-outputs = true # Nice for developers
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gc-keep-derivations = true # Idem
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env-keep-derivations = false
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</programlisting>
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<para>You can override settings using the <option>--option</option>
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flag, e.g. <literal>--option gc-keep-outputs 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-gc-keep-outputs"><term><literal>gc-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-gc-keep-derivations"><term><literal>gc-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 safe a bit of disk space (or a lot if
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<literal>gc-keep-outputs</literal> is also turned on).</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>env-keep-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>gc-keep-outputs</literal>.</para>
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<para>The difference between this option and
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<literal>gc-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>gc-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-build-max-jobs"><term><literal>build-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>. You should generally set it to the number
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of CPUs in your system (e.g., <literal>2</literal> on a Athlon 64
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X2). It can be overriden 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-build-cores"><term><literal>build-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 overriden 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-build-max-silent-time"><term><literal>build-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 a 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 overriden 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-build-timeout"><term><literal>build-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 a 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 overriden 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-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>build-use-chroot</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>chroot environment</emphasis>, i.e., the
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build will be isolated from the normal file system hierarchy and
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will only see the Nix store, the temporary build directory, and
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the directories configured with the <link
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linkend='conf-build-chroot-dirs'><literal>build-chroot-dirs</literal>
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option</link> (such as <filename>/proc</filename> and
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<filename>/dev</filename>). This is useful to prevent undeclared
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dependencies on files in directories such as
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<filename>/usr/bin</filename>.</para>
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<para>The use of a chroot requires that Nix is run as root (but
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you can still use the <link
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linkend='conf-build-users-group'>“build users” feature</link> to
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perform builds under different users than root). Currently,
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chroot builds only work on Linux because Nix uses “bind mounts” to
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make the Nix store and other directories available inside the
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chroot.</para>
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</listitem>
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</varlistentry>
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<varlistentry><term><literal>build-use-substitutes</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>build-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 xml:id="conf-build-chroot-dirs"><term><literal>build-chroot-dirs</literal></term>
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<listitem><para>When builds are performed in a chroot environment,
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Nix will mount (using <command>mount --bind</command> on Linux)
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some directories from the normal file system hierarchy inside the
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chroot. These are the Nix store, the temporary build directory
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(usually
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<filename>/tmp/nix-<replaceable>pid</replaceable>-<replaceable>number</replaceable></filename>)
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and the directories listed here. The default is <literal>dev
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/proc</literal>. Files in <filename>/dev</filename> (such as
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<filename>/dev/null</filename>) are needed by many builds, and
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some files in <filename>/proc</filename> may also be needed
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occasionally.</para>
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<para>The value used on NixOS is
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<programlisting>
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build-use-chroot = /dev /proc /bin</programlisting>
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to make the <filename>/bin/sh</filename> symlink available (which
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is still needed by many builders).</para>
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</listitem>
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</varlistentry>
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<varlistentry><term><literal>build-cache-failures</literal></term>
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<listitem><para>If set to <literal>true</literal>, Nix will
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“cache” build failures, meaning that it will remember (in its
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database) that a derivation previously failed. If you then try to
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build the derivation again, Nix will immediately fail rather than
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perform the build again. Failures in fixed-output derivations
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(such as <function>fetchurl</function> calls) are never cached.
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The “failed” status of a derivation can be cleared using
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<command>nix-store --clear-failed-paths</command>. By default,
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failure caching is disabled.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>build-keep-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>build-compress-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>binary-caches</literal></term>
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<listitem><para>A list of URLs of binary caches, separated by
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whitespace. The default is empty.<!-- The default is
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<literal>http://nixos.org/binary-cache</literal>. --></para></listitem>
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</varlistentry>
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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/root/channels/binary-caches/*</literal>,
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which ensures that Nix will use the binary caches corresponding to
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the channels installed by root. Do not set this option to read
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files created by untrusted users!</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>trusted-binary-caches</literal></term>
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<listitem><para>A list of URLs of binary caches, 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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binary-caches <replaceable>urls</replaceable></literal> on the
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command line. Daemon users are only allowed to pass a subset of
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the URLs listed in <literal>binary-caches</literal> and
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<literal>trusted-binary-caches</literal>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>binary-caches-parallel-connections</literal></term>
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<listitem><para>The maximum number of parallel HTTP connections
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used by the binary cache substituter to get NAR info files. This
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number should be high to minimise latency. It defaults to
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150.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>force-manifest</literal></term>
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<listitem><para>If this option is set to <literal>false</literal>
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(default) and a Nix channel provides both a manifest and a binary
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cache, only the binary cache will be used. If set to
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<literal>true</literal>, the manifest will be fetched as well.
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This is useful if you want to use binary patches (which are
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currently not supported by binary caches).</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
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<literal>powerpc-darwin</literal>. Nix can only build derivations
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whose <literal>system</literal> attribute equals the value
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specified here. In general, it never makes sense to modify this
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value from its default, since you can use it to ‘lie’ about the
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platform you are building on (e.g., perform a Mac OS build on a
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Linux machine; the result would obviously be wrong). It only
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makes sense if the Nix binaries can run on multiple platforms,
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e.g., ‘universal binaries’ that run on <literal>powerpc-darwin</literal> and
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<literal>i686-darwin</literal>.</para>
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<para>It defaults to the canonical Nix system name detected by
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<filename>configure</filename> at build time.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>fsync-metadata</literal></term>
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<listitem><para>If set to <literal>true</literal>, changes to the
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Nix store metadata (in <filename>/nix/var/nix/db</filename>) are
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synchronously flushed to disk. This improves robustness in case
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of system crashes, but reduces performance. The default is
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<literal>true</literal>.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal>auto-optimise-store</literal></term>
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<listitem><para>If set to <literal>true</literal> (the default),
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Nix automatically detects files in the store that have identical
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contents, and replaces them with hard links to a single copy.
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This saves disk space. If set to <literal>false</literal>, you
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can still run <command>nix-store --optimise</command> to get rid
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of duplicate files.</para></listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsection>
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</refentry>
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