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Manual: Kernel configuration

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Eelco Dolstra 2013-08-20 16:14:29 +02:00
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doc/manual/configuration.xml
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@ -74,7 +74,7 @@ different channels that you might have.)</para>
<command>nixos-rebuild switch</command>.</para>
<section><title>Customising packages</title>
<section xml:id="sec-customising-packages"><title>Customising packages</title>
<para>Some packages in Nixpkgs have options to enable or disable
optional functionality or change other aspects of the package. For
@ -738,6 +738,72 @@ networking.localCommands =
</section>
<!--===============================================================-->
<section><title>Linux kernel</title>
<para>You can override the Linux kernel and associated packages using
the option <option>boot.kernelPackages</option>. For instance, this
selects the Linux 3.10 kernel:
<programlisting>
boot.kernelPackages = pkgs.kernelPackages_3_10;
</programlisting>
Note that this not only replaces the kernel, but also packages that
are specific to the kernel version, such as the NVIDIA video drivers.
This ensures that driver packages are consistent with the
kernel.</para>
<para>The default Linux kernel configuration should be fine for most
users. You can see the configuration of your current kernel in
<filename>/run/booted-system/kernel-modules/config</filename>. If you
want to change the kernel configuration, you can use the
<option>packageOverrides</option> feature (see <xref
linkend="sec-customising-packages" />). For instance, to enable
support for the kernel debugger KGDB:
<programlisting>
nixpkgs.config.packageOverrides = pkgs:
{ linux_3_4 = pkgs.linux_3_4.override {
extraConfig =
''
KGDB y
'';
};
};
</programlisting>
<varname>extraConfig</varname> takes a list of Linux kernel
configuration options, one per line. The name of the option should
not include the prefix <literal>CONFIG_</literal>. The option value
is typically <literal>y</literal>, <literal>n</literal> or
<literal>m</literal> (to build something as a kernel module).</para>
<para>Kernel modules for hardware devices are generally loaded
automatically by <command>udev</command>. You can force a module to
be loaded via <option>boot.kernelModules</option>, e.g.
<programlisting>
boot.kernelModules = [ "fuse" "kvm-intel" "coretemp" ];
</programlisting>
If the module is required early during the boot (e.g. to mount the
root file system), you can use
<option>boot.initrd.extraKernelModules</option>:
<programlisting>
boot.initrd.extraKernelModules = [ "cifs" ];
</programlisting>
This causes the specified modules and their dependencies to be added
to the initial ramdark.</para>
<para>Kernel runtime parameters can be set through
<option>boot.kernel.sysctl</option>, e.g.
<programlisting>
boot.kernel.sysctl."net.ipv4.tcp_keepalive_time" = 120;
</programlisting>
sets the kernel’s TCP keepalive time to 120 seconds. To see the
available parameters, run <command>sysctl -a</command>.</para>
</section>
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