Manual: Update chapter on remote builds
Alos add a command "nix ping-store" to make it easier to see if Nix can connect to a remote builder (e.g. 'nix ping-store --store ssh://mac').
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Eelco Dolstra
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3 changed files with 187 additions and 66 deletions
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@ -4,71 +4,109 @@
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version="5.0"
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xml:id='chap-distributed-builds'>
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<title>Distributed Builds</title>
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<title>Remote Builds</title>
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<para>Nix supports distributed builds, where a local Nix installation can
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forward Nix builds to other machines over the network. This allows
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multiple builds to be performed in parallel (thus improving
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performance) and allows Nix to perform multi-platform builds in a
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semi-transparent way. For instance, if you perform a build for a
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<literal>x86_64-darwin</literal> on an <literal>i686-linux</literal>
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machine, Nix can automatically forward the build to a
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<literal>x86_64-darwin</literal> machine, if available.</para>
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<para>Nix supports remote builds, where a local Nix installation can
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forward Nix builds to other machines. This allows multiple builds to
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be performed in parallel and allows Nix to perform multi-platform
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builds in a semi-transparent way. For instance, if you perform a
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build for a <literal>x86_64-darwin</literal> on an
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<literal>i686-linux</literal> machine, Nix can automatically forward
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the build to a <literal>x86_64-darwin</literal> machine, if
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available.</para>
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<para>You can enable distributed builds by setting the environment
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variable <envar>NIX_BUILD_HOOK</envar> to point to a program that Nix
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will call whenever it wants to build a derivation. The build hook
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(typically a shell or Perl script) can decline the build, in which Nix
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will perform it in the usual way if possible, or it can accept it, in
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which case it is responsible for somehow getting the inputs of the
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build to another machine, doing the build there, and getting the
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results back.</para>
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<para>To forward a build to a remote machine, it’s required that the
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remote machine is accessible via SSH and that it has Nix
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installed. You can test whether connecting to the remote Nix instance
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works, e.g.
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<example xml:id='ex-remote-systems'><title>Remote machine configuration:
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<filename>remote-systems.conf</filename></title>
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<programlisting>
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nix@mcflurry.labs.cs.uu.nl x86_64-darwin /home/nix/.ssh/id_quarterpounder_auto 2
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nix@scratchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 1 kvm
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nix@itchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 2
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nix@poochie.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 2 kvm perf
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</programlisting>
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</example>
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<screen>
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$ nix ping-store --store ssh://mac
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</screen>
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<para>Nix ships with a build hook that should be suitable for most
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purposes. It uses <command>ssh</command> and
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<command>nix-copy-closure</command> to copy the build inputs and
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outputs and perform the remote build. To use it, you should set
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<envar>NIX_BUILD_HOOK</envar> to
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<filename><replaceable>prefix</replaceable>/libexec/nix/build-remote</filename>.
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You should also define a list of available build machines and point
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the environment variable <envar>NIX_REMOTE_SYSTEMS</envar> to
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it. <envar>NIX_REMOTE_SYSTEMS</envar> must be an absolute path. An
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example configuration is shown in <xref linkend='ex-remote-systems'
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/>. Each line in the file specifies a machine, with the following
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bits of information:
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will try to connect to the machine named <literal>mac</literal>. It is
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possible to specify an SSH identity file as part of the remote store
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URI, e.g.
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<screen>
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$ nix ping-store --store ssh://mac?ssh-key=/home/alice/my-key
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</screen>
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Since builds should be non-interactive, the key should not have a
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passphrase. Alternatively, you can load identities ahead of time into
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<command>ssh-agent</command> or <command>gpg-agent</command>.</para>
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<para>If you get the error
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<screen>
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bash: nix-store: command not found
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error: cannot connect to 'mac'
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</screen>
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then you need to ensure that the <envar>PATH</envar> of
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non-interactive login shells contains Nix.</para>
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<warning><para>If you are building via the Nix daemon, it is the Nix
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daemon user account (that is, <literal>root</literal>) that should
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have SSH access to the remote machine. If you can’t or don’t want to
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configure <literal>root</literal> to be able to access to remote
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machine, you can use a private Nix store instead by passing
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e.g. <literal>--store ~/my-nix</literal>.</para></warning>
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<para>The list of remote machines can be specified on the command line
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or in the Nix configuration file. The former is convenient for
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testing. For example, the following command allows you to build a
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derivation for <literal>x86_64-darwin</literal> on a Linux machine:
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<screen>
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$ uname
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Linux
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$ nix build \
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'(with import <nixpkgs> { system = "x86_64-darwin"; }; runCommand "foo" {} "uname > $out")' \
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--builders 'ssh://mac x86_64-darwin'
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[1/0/1 built, 0.0 MiB DL] building foo on ssh://mac
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$ cat ./result
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Darwin
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</screen>
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It is possible to specify multiple builders separated by a semicolon
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or a newline, e.g.
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<screen>
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--builders 'ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd'
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</screen>
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</para>
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<para>Each machine specification consists of the following elements,
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separated by spaces. Only the first element is required.
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<orderedlist>
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<listitem><para>The name of the remote machine, with optionally the
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user under which the remote build should be performed. This is
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actually passed as an argument to <command>ssh</command>, so it can
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be an alias defined in your
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<listitem><para>The URI of the remote store in the format
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<literal>ssh://[<replaceable>username</replaceable>@]<replaceable>hostname</replaceable></literal>,
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e.g. <literal>ssh://nix@mac</literal> or
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<literal>ssh://mac</literal>. For backward compatibility,
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<literal>ssh://</literal> may be omitted. The hostname may be an
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alias defined in your
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<filename>~/.ssh/config</filename>.</para></listitem>
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<listitem><para>A comma-separated list of Nix platform type
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identifiers, such as <literal>x86_64-darwin</literal>. It is
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possible for a machine to support multiple platform types, e.g.,
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<literal>i686-linux,x86_64-linux</literal>.</para></listitem>
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<literal>i686-linux,x86_64-linux</literal>. If omitted, this
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defaults to the local platform type.</para></listitem>
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<listitem><para>The SSH private key to be used to log in to the
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remote machine. Since builds should be non-interactive, this key
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should not have a passphrase!</para></listitem>
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<listitem><para>The SSH identity file to be used to log in to the
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remote machine. If omitted, SSH will use its regular
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identities.</para></listitem>
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<listitem><para>The maximum number of builds that
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<filename>build-remote</filename> will execute in parallel on the
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machine. Typically this should be equal to the number of CPU cores.
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For instance, the machine <literal>itchy</literal> in the example
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will execute up to 8 builds in parallel.</para></listitem>
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<listitem><para>The maximum number of builds that Nix will execute
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in parallel on the machine. Typically this should be equal to the
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number of CPU cores. For instance, the machine
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<literal>itchy</literal> in the example will execute up to 8 builds
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in parallel.</para></listitem>
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<listitem><para>The “speed factor”, indicating the relative speed of
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the machine. If there are multiple machines of the right type, Nix
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@ -76,30 +114,69 @@ bits of information:
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<listitem><para>A comma-separated list of <emphasis>supported
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features</emphasis>. If a derivation has the
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<varname>requiredSystemFeatures</varname> attribute, then
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<filename>build-remote</filename> will only perform the
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derivation on a machine that has the specified features. For
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instance, the attribute
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<varname>requiredSystemFeatures</varname> attribute, then Nix will
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only perform the derivation on a machine that has the specified
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features. For instance, the attribute
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<programlisting>
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requiredSystemFeatures = [ "kvm" ];
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</programlisting>
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will cause the build to be performed on a machine that has the
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<literal>kvm</literal> feature (i.e., <literal>scratchy</literal> in
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the example above).</para></listitem>
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<literal>kvm</literal> feature.</para></listitem>
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<listitem><para>A comma-separated list of <emphasis>mandatory
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features</emphasis>. A machine will only be used to build a
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derivation if all of the machine’s mandatory features appear in the
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derivation’s <varname>requiredSystemFeatures</varname> attribute.
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Thus, in the example, the machine <literal>poochie</literal> will
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only do derivations that have
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<varname>requiredSystemFeatures</varname> set to <literal>["kvm"
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"perf"]</literal> or <literal>["perf"]</literal>.</para></listitem>
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derivation’s <varname>requiredSystemFeatures</varname>
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attribute..</para></listitem>
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</orderedlist>
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</para>
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For example, the machine specification
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<programlisting>
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nix@scratchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 1 kvm
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nix@itchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 2
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nix@poochie.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 1 2 kvm benchmark
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</programlisting>
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specifies several machines that can perform
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<literal>i686-linux</literal> builds. However,
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<literal>poochie</literal> will only do builds that have the attribute
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<programlisting>
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requiredSystemFeatures = [ "benchmark" ];
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</programlisting>
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or
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<programlisting>
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requiredSystemFeatures = [ "benchmark" "kvm" ];
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</programlisting>
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<literal>itchy</literal> cannot do builds that require
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<literal>kvm</literal>, but <literal>scratchy</literal> does support
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such builds. For regular builds, <literal>itchy</literal> will be
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preferred over <literal>scratchy</literal> because it has a higher
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speed factor.</para>
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<para>Remote builders can also be configured in
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<filename>nix.conf</filename>, e.g.
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<programlisting>
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builders = ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd
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</programlisting>
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Finally, remote builders can be configured in a separate configuration
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file included in <option>builders</option> via the syntax
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<literal>@<replaceable>file</replaceable></literal>. For example,
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<programlisting>
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builders = @/etc/nix/machines
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</programlisting>
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causes the list of machines in <filename>/etc/nix/machines</filename>
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to be included. (This is the default.)</para>
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</chapter>
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@ -763,7 +763,7 @@ builtins.fetchurl {
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more details.
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</para>
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<para>
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Since these files are loaded into the same address space as
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Since these files are loaded into the same address space as
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Nix itself, they must be DSOs compatible with the instance of
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Nix running at the time (i.e. compiled against the same
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headers, not linked to any incompatible libraries). They
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@ -771,14 +771,23 @@ builtins.fetchurl {
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be available already at load time.
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</para>
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<para>
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If an entry in the list is a directory, all files in the
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directory are loaded as plugins (non-recursively).
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If an entry in the list is a directory, all files in the
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directory are loaded as plugins (non-recursively).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry xml:id="conf-builders">
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<term><literal>builders</literal></term>
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<listitem>
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<para>A list of machines on which to perform builds. <phrase
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condition="manual">See <xref linkend="chap-distributed-builds"
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/> for details.</phrase></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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35
src/nix/ping-store.cc
Normal file
35
src/nix/ping-store.cc
Normal file
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@ -0,0 +1,35 @@
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#include "command.hh"
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#include "shared.hh"
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#include "store-api.hh"
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using namespace nix;
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struct CmdPingStore : StoreCommand
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{
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std::string name() override
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{
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return "ping-store";
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}
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std::string description() override
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{
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return "test whether a store can be opened";
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}
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Examples examples() override
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{
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return {
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Example{
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"To test whether connecting to a remote Nix store via SSH works:",
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"nix ping-store --store ssh://mac1"
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},
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};
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}
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void run(ref<Store> store) override
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{
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store->connect();
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}
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};
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static RegisterCommand r1(make_ref<CmdPingStore>());
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