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139 lines
5 KiB
XML
139 lines
5 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>
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You can override the Linux kernel and associated packages using the option
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<option>boot.kernelPackages</option>. For instance, this selects the Linux
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3.10 kernel:
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<programlisting>
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<xref linkend="opt-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 are
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specific to the kernel version, such as the NVIDIA video drivers. This
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ensures that driver packages are consistent with the kernel.
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</para>
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<para>
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The default Linux kernel configuration should be fine for most users. You can
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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
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<xref
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linkend="sec-customising-packages" />). For instance, to enable support
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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 configuration
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options, one per line. The name of the option should not include the prefix
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<literal>CONFIG_</literal>. The option value is typically
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<literal>y</literal>, <literal>n</literal> or <literal>m</literal> (to build
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something as a kernel module).
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</para>
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<para>
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Kernel modules for hardware devices are generally loaded automatically by
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<command>udev</command>. You can force a module to be loaded via
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<xref linkend="opt-boot.kernelModules"/>, e.g.
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<programlisting>
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<xref linkend="opt-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 root file
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system), you can use <xref linkend="opt-boot.initrd.kernelModules"/>:
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<programlisting>
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<xref linkend="opt-boot.initrd.kernelModules"/> = [ "cifs" ];
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</programlisting>
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This causes the specified modules and their dependencies to be added to the
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initial ramdisk.
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</para>
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<para>
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Kernel runtime parameters can be set through
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<xref linkend="opt-boot.kernel.sysctl"/>, e.g.
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<programlisting>
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<xref linkend="opt-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 available
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parameters, run <command>sysctl -a</command>.
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</para>
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<section xml:id="sec-linux-config-customizing">
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<title>Customize your kernel</title>
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<para>
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The first step before compiling the kernel is to generate an appropriate
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<literal>.config</literal> configuration. Either you pass your own config
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via the <literal>configfile</literal> setting of
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<literal>linuxManualConfig</literal>:
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<screen><![CDATA[
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custom-kernel = super.linuxManualConfig {
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inherit (super) stdenv hostPlatform;
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inherit (linux_4_9) src;
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version = "${linux_4_9.version}-custom";
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configfile = /home/me/my_kernel_config;
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allowImportFromDerivation = true;
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};
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]]></screen>
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You can edit the config with this snippet (by default <command>make
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menuconfig</command> won't work out of the box on nixos):
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<screen><![CDATA[
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nix-shell -E 'with import <nixpkgs> {}; kernelToOverride.overrideAttrs (o: {nativeBuildInputs=o.nativeBuildInputs ++ [ pkgconfig ncurses ];})'
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]]></screen>
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or you can let nixpkgs generate the configuration. Nixpkgs generates it via
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answering the interactive kernel utility <command>make config</command>. The
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answers depend on parameters passed to
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<filename>pkgs/os-specific/linux/kernel/generic.nix</filename> (which you
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can influence by overriding <literal>extraConfig, autoModules,
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modDirVersion, preferBuiltin, extraConfig</literal>).
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<screen><![CDATA[
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mptcp93.override ({
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name="mptcp-local";
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ignoreConfigErrors = true;
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autoModules = false;
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kernelPreferBuiltin = true;
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enableParallelBuilding = true;
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extraConfig = ''
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DEBUG_KERNEL y
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FRAME_POINTER y
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KGDB y
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KGDB_SERIAL_CONSOLE y
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DEBUG_INFO y
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'';
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});
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]]></screen>
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</para>
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</section>
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<section xml:id="sec-linux-config-developing-modules">
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<title>Developing kernel modules</title>
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<para>
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When developing kernel modules it's often convenient to run edit-compile-run
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loop as quickly as possible. See below snippet as an example of developing
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<literal>mellanox</literal> 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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