Linux kernel: Difference between revisions

You can choose your kernel simply by setting the <code>boot.kernelPackages</code> option

For example by adding this to  <code>/etc/nixos/configuration.nix</code>:

boot.kernelPackages = pkgs.linuxKernel.packages.linuxPackages_latest;

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And rebuild your system and reboot to use your new kernel:

pkgs.linuxPackages                          pkgs.linuxPackages_latest

pkgs.linuxPackages-libre                    pkgs.linuxPackages_latest-libre

pkgs.linuxPackages-rt                        pkgs.linuxPackages_latest_hardened

pkgs.linuxPackages-rt_5_4                    pkgs.linuxPackages_latest_xen_dom0

pkgs.linuxPackages-rt_5_6                    pkgs.linuxPackages_latest_xen_dom0_hardened

pkgs.linuxPackages-rt_latest                pkgs.linuxPackages_mptcp

pkgs.linuxPackagesFor                        pkgs.linuxPackages_rpi0

pkgs.linuxPackages_4_14                     pkgs.linuxPackages_rpi1

pkgs.linuxPackages_4_19                      pkgs.linuxPackages_rpi2

pkgs.linuxPackages_4_4                      pkgs.linuxPackages_rpi3

pkgs.linuxPackages_4_9                      pkgs.linuxPackages_rpi4

pkgs.linuxPackages_5_4                      pkgs.linuxPackages_testing

pkgs.linuxPackages_5_8                       pkgs.linuxPackages_testing_bcachefs

pkgs.linuxPackages_5_9                       pkgs.linuxPackages_testing_hardened

pkgs.linuxPackages_custom                    pkgs.linuxPackages_xen_dom0

pkgs.linuxPackages_custom_tinyconfig_kernel  pkgs.linuxPackages_xen_dom0_hardened

pkgs.linuxPackages_hardened                  pkgs.linuxPackages_zen

pkgs.linuxPackages_hardkernel_4_14

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You can use <code>boot.extraModprobeConfig</code>, which is analogous to creating modprobe.conf files in /etc/modprobe.d/ in regular Linux distributions. This can be used for both built-in and loadable kernel modules.  

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boot.extraModprobeConfig = ''

  # example settings

  options yourmodulename optionA=valueA optionB=valueB # syntax

  options thinkpad_acpi  fan_control=1                # example #1 kernel module parameter

  options usbcore        blinkenlights=1              # example #2 kernel module parameter

'';

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The config attribute <code>boot.kernelParams</code> can be set to supply the Linux kernel with additional command line arguments at boot time. It can only be used for built-in modules.

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   boot.kernelParams = [  

     "usbcore.blinkenlights=1" # example kernel module parameter

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It is sometimes desirable to change the configuration of your kernel, while keeping the kernel version itself managed through Nixpkgs. To do so, you can add the configuration to a dummy {{nixos:option|boot.kernelPatches}},<ref>[https://logs.nix.samueldr.com/nixos/2018-05-09#1525898458-1525898534; #nixos 2018-05-09]</ref><ref>[https://github.com/NixOS/nixpkgs/blob/03d4694e6110fa9c16e88ee74085ea2068c27494/nixos/modules/misc/crashdump.nix#L63-L73 <tt>nixos/modules/misc/crashdump.nix#L63-L73</tt>]</ref> which will then be merged and applied to the current kernel. As with kernel configuration with NixOS, drop the <tt>CONFIG_</tt> prefix from the kernel configuration names.

This example is from the {{nixos:option|boot.crashDump.enable}} option:

      boot.kernelPatches = [ {

        name = "crashdump-config";

        patch = null;

        extraConfig = ''

                CRASH_DUMP y

                DEBUG_INFO y

                PROC_VMCORE y

                LOCKUP_DETECTOR y

                HARDLOCKUP_DETECTOR y

              '';

        } ];

Another way to build a kernel with custom configuration is to create a overlay and use either <tt>extraConfig</tt> or <tt>structuredExtraConfig</tt>. This allows for more flexibility, since you can basically override any kernel option available here <ref>[https://github.com/NixOS/nixpkgs/blob/e6db435973160591fe7348876a5567c729495175/pkgs/os-specific/linux/kernel/generic.nix#L11-L56<tt>pkgs/os-specific/linux/kernel/generic.nix#L11-L56</tt>]</ref>. Using <tt>structuredExtraConfig</tt> is recommended since there is some sanity check if the options you're passing to your kernel is correct. Also, setting <tt>ignoreConfigErrors</tt> is useful to avoid <tt>error: unused option</tt> during build.

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         linuxZenWMuQSS = pkgs.linuxPackagesFor (pkgs.linux_zen.kernel.override {

           ignoreConfigErrors = true;

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boot.kernelPackages = pkgs.linuxPackagesFor (pkgs.linux_4_19.override {

             url = "mirror://kernel/linux/kernel/v4.x/linux-${version}.tar.xz";

      };

</syntaxhighlight>

As dependencies between kernel configurations items need to be addressed manually, use <code>--keep-failed</code> to inspect the intermediate nix config file after for instance the error

== Embedded Linux Cross-compile xconfig and menuconfig ==

This section details the on how to get an environment that can be used to configure and cross-compile the kernel for embedded Linux development. The kernel source won't come from nix unpack phase but rather gotten externally(such as from the chip vendor github). So first clone the kernel source, then use the shell.nix below to set up the dev environment(example below is for aarch64):

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let

       pkgconfig

}).env

Finally, cd to the kernel source dir and do development normally.

It is (currently) not possible to run <code>make menuconfig</code> in the checked out linux kernel sources. This is because <code>ncurses</code> is not part of your working environment when you start it with <code>nix-shell '<nixpkgs>' -A linuxPackages.kernel</code>.

This nix-shell hack adds ncurses as a build dependency to the kernel:

$ nix-shell -E 'with import <nixpkgs> {}; linux.overrideAttrs (o: {nativeBuildInputs=o.nativeBuildInputs ++ [ pkg-config ncurses ];})'

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{ stdenv, lib, fetchFromGitHub, kernel, kmod }:

   name = "v4l2loopback-dc-${version}-${kernel.version}";

     sha256 = "1d9qpnmqa3pfwsrpjnxdz76ipk4w37bbxyrazchh4vslnfc886fx";

   makeFlags = [

   meta = with lib; {

     license = licenses.gpl2;

     maintainers = [ maintainers.makefu ];

     platforms = platforms.linux;

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See also:  {{manual:nixos|sec=#sec-linux-config-developing-modules|chapter=12.2. Developing kernel modules}}

Note that if you don't reboot, you can still load manually the module using <code>modprobe yourmodulename></code>, and to automatically enable a module during configuration switch/reboot, you can put <code>modprobe yourmodulename || true</code> inside the script of a systemctl service (it is for example what does wireguard).

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}

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     })

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turn off `DEBUG_INFO_BTF`