Manual: Kernel configuration

doc/manual/configuration.xml

@@ -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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