141 lines
4.2 KiB
Markdown
141 lines
4.2 KiB
Markdown
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# Linux Kernel {#sec-kernel-config}
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You can override the Linux kernel and associated packages using the
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option `boot.kernelPackages`. For instance, this selects the Linux 3.10
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kernel:
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```nix
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boot.kernelPackages = pkgs.linuxKernel.packages.linux_3_10;
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```
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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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While `pkgs.linuxKernel.packages` contains all available kernel packages,
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you may want to use one of the unversioned `pkgs.linuxPackages_*` aliases
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such as `pkgs.linuxPackages_latest`, that are kept up to date with new
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versions.
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The default Linux kernel configuration should be fine for most users.
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You can see the configuration of your current kernel with the following
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command:
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```ShellSession
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zcat /proc/config.gz
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```
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If you want to change the kernel configuration, you can use the
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`packageOverrides` feature (see [](#sec-customising-packages)). For
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instance, to enable support for the kernel debugger KGDB:
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```nix
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nixpkgs.config.packageOverrides = pkgs: pkgs.lib.recursiveUpdate pkgs {
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linuxKernel.kernels.linux_5_10 = pkgs.linuxKernel.kernels.linux_5_10.override {
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extraConfig = ''
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KGDB y
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'';
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};
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};
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```
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`extraConfig` takes a list of Linux kernel configuration options, one
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per line. The name of the option should not include the prefix
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`CONFIG_`. The option value is typically `y`, `n` or `m` (to build
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something as a kernel module).
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Kernel modules for hardware devices are generally loaded automatically
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by `udev`. You can force a module to be loaded via
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[](#opt-boot.kernelModules), e.g.
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```nix
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boot.kernelModules = [ "fuse" "kvm-intel" "coretemp" ];
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```
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If the module is required early during the boot (e.g. to mount the root
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file system), you can use [](#opt-boot.initrd.kernelModules):
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```nix
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boot.initrd.kernelModules = [ "cifs" ];
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```
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This causes the specified modules and their dependencies to be added to
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the initial ramdisk.
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Kernel runtime parameters can be set through
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[](#opt-boot.kernel.sysctl), e.g.
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```nix
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boot.kernel.sysctl."net.ipv4.tcp_keepalive_time" = 120;
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```
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sets the kernel's TCP keepalive time to 120 seconds. To see the
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available parameters, run `sysctl -a`.
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## Customize your kernel {#sec-linux-config-customizing}
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The first step before compiling the kernel is to generate an appropriate
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`.config` configuration. Either you pass your own config via the
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`configfile` setting of `linuxKernel.manualConfig`:
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```nix
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custom-kernel = let base_kernel = linuxKernel.kernels.linux_4_9;
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in super.linuxKernel.manualConfig {
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inherit (super) stdenv hostPlatform;
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inherit (base_kernel) src;
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version = "${base_kernel.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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```
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You can edit the config with this snippet (by default `make
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menuconfig` won\'t work out of the box on nixos):
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```ShellSession
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nix-shell -E 'with import <nixpkgs> {}; kernelToOverride.overrideAttrs (o: {nativeBuildInputs=o.nativeBuildInputs ++ [ pkg-config ncurses ];})'
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```
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or you can let nixpkgs generate the configuration. Nixpkgs generates it
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via answering the interactive kernel utility `make config`. The answers
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depend on parameters passed to
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`pkgs/os-specific/linux/kernel/generic.nix` (which you can influence by
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overriding `extraConfig, autoModules,
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modDirVersion, preferBuiltin, extraConfig`).
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```nix
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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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```
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## Developing kernel modules {#sec-linux-config-developing-modules}
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When developing kernel modules it\'s often convenient to run
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edit-compile-run loop as quickly as possible. See below snippet as an
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example of developing `mellanox` drivers.
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```ShellSession
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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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```
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