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91 lines
3.1 KiB
XML
91 lines
3.1 KiB
XML
<chapter 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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version="5.0"
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xml:id="sec-kernel-config">
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<title>Linux Kernel</title>
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<para>You can override the Linux kernel and associated packages using
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the option <option>boot.kernelPackages</option>. For instance, this
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selects the Linux 3.10 kernel:
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<programlisting>
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boot.kernelPackages = pkgs.linuxPackages_3_10;
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</programlisting>
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Note that this not only replaces the kernel, but also packages that
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are specific to the kernel version, such as the NVIDIA video drivers.
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This ensures that driver packages are consistent with the
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kernel.</para>
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<para>The default Linux kernel configuration should be fine for most users. You can see the configuration of your current kernel with the following command:
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<programlisting>
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zcat /proc/config.gz
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</programlisting>
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If you want to change the kernel configuration, you can use the
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<option>packageOverrides</option> feature (see <xref
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linkend="sec-customising-packages" />). For instance, to enable
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support for the kernel debugger KGDB:
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<programlisting>
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nixpkgs.config.packageOverrides = pkgs:
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{ linux_3_4 = pkgs.linux_3_4.override {
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extraConfig =
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''
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KGDB y
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'';
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};
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};
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</programlisting>
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<varname>extraConfig</varname> takes a list of Linux kernel
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configuration options, one per line. The name of the option should
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not include the prefix <literal>CONFIG_</literal>. The option value
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is typically <literal>y</literal>, <literal>n</literal> or
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<literal>m</literal> (to build something as a kernel module).</para>
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<para>Kernel modules for hardware devices are generally loaded
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automatically by <command>udev</command>. You can force a module to
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be loaded via <option>boot.kernelModules</option>, e.g.
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<programlisting>
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boot.kernelModules = [ "fuse" "kvm-intel" "coretemp" ];
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</programlisting>
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If the module is required early during the boot (e.g. to mount the
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root file system), you can use
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<option>boot.initrd.extraKernelModules</option>:
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<programlisting>
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boot.initrd.extraKernelModules = [ "cifs" ];
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</programlisting>
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This causes the specified modules and their dependencies to be added
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to the initial ramdisk.</para>
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<para>Kernel runtime parameters can be set through
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<option>boot.kernel.sysctl</option>, e.g.
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<programlisting>
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boot.kernel.sysctl."net.ipv4.tcp_keepalive_time" = 120;
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</programlisting>
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sets the kernel’s TCP keepalive time to 120 seconds. To see the
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available parameters, run <command>sysctl -a</command>.</para>
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<section>
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<title>Developing kernel modules</title>
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<para>When developing kernel modules it's often convenient to run
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edit-compile-run loop as quickly as possible.
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See below snippet as an example of developing <literal>mellanox</literal>
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drivers.
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</para>
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<screen><![CDATA[
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$ nix-build '<nixpkgs>' -A linuxPackages.kernel.dev
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$ nix-shell '<nixpkgs>' -A linuxPackages.kernel
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$ unpackPhase
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$ cd linux-*
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$ make -C $dev/lib/modules/*/build M=$(pwd)/drivers/net/ethernet/mellanox modules
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# insmod ./drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.ko
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]]></screen>
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</section>
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</chapter>
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