pyrox.dev
1<chapter xmlns="http://docbook.org/ns/docbook"
2 xmlns:xlink="http://www.w3.org/1999/xlink"
3 xmlns:xi="http://www.w3.org/2001/XInclude"
4 version="5.0"
5 xml:id="sec-kernel-config">
6
7<title>Linux Kernel</title>
8
9<para>You can override the Linux kernel and associated packages using
10the option <option>boot.kernelPackages</option>. For instance, this
11selects the Linux 3.10 kernel:
12<programlisting>
13boot.kernelPackages = pkgs.linuxPackages_3_10;
14</programlisting>
15Note that this not only replaces the kernel, but also packages that
16are specific to the kernel version, such as the NVIDIA video drivers.
17This ensures that driver packages are consistent with the
18kernel.</para>
19
20<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:
21<programlisting>
22zcat /proc/config.gz
23</programlisting>
24If you want to change the kernel configuration, you can use the
25<option>packageOverrides</option> feature (see <xref
26linkend="sec-customising-packages" />). For instance, to enable
27support for the kernel debugger KGDB:
28
29<programlisting>
30nixpkgs.config.packageOverrides = pkgs:
31 { linux_3_4 = pkgs.linux_3_4.override {
32 extraConfig =
33 ''
34 KGDB y
35 '';
36 };
37 };
38</programlisting>
39
40<varname>extraConfig</varname> takes a list of Linux kernel
41configuration options, one per line. The name of the option should
42not include the prefix <literal>CONFIG_</literal>. The option value
43is typically <literal>y</literal>, <literal>n</literal> or
44<literal>m</literal> (to build something as a kernel module).</para>
45
46<para>Kernel modules for hardware devices are generally loaded
47automatically by <command>udev</command>. You can force a module to
48be loaded via <option>boot.kernelModules</option>, e.g.
49<programlisting>
50boot.kernelModules = [ "fuse" "kvm-intel" "coretemp" ];
51</programlisting>
52If the module is required early during the boot (e.g. to mount the
53root file system), you can use
54<option>boot.initrd.extraKernelModules</option>:
55<programlisting>
56boot.initrd.extraKernelModules = [ "cifs" ];
57</programlisting>
58This causes the specified modules and their dependencies to be added
59to the initial ramdisk.</para>
60
61<para>Kernel runtime parameters can be set through
62<option>boot.kernel.sysctl</option>, e.g.
63<programlisting>
64boot.kernel.sysctl."net.ipv4.tcp_keepalive_time" = 120;
65</programlisting>
66sets the kernel’s TCP keepalive time to 120 seconds. To see the
67available parameters, run <command>sysctl -a</command>.</para>
68
69<section>
70 <title>Developing kernel modules</title>
71
72 <para>When developing kernel modules it's often convenient to run
73 edit-compile-run loop as quickly as possible.
74
75 See below snippet as an example of developing <literal>mellanox</literal>
76 drivers.
77 </para>
78
79 <screen><![CDATA[
80$ nix-build '<nixpkgs>' -A linuxPackages.kernel.dev
81$ nix-shell '<nixpkgs>' -A linuxPackages.kernel
82$ unpackPhase
83$ cd linux-*
84$ make -C $dev/lib/modules/*/build M=$(pwd)/drivers/net/ethernet/mellanox modules
85# insmod ./drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.ko
86]]></screen>
87
88</section>
89
90</chapter>