138 lines
4.7 KiB
Markdown
138 lines
4.7 KiB
Markdown
# 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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Please note that the current convention in NixOS is to only keep actively
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maintained kernel versions on both unstable and the currently supported stable
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release(s) of NixOS. This means that a non-longterm kernel will be removed after it's
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abandoned by the kernel developers, even on stable NixOS versions. If you
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pin your kernel onto a non-longterm version, expect your evaluation to fail as
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soon as the version is out of maintenance.
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Longterm versions of kernels will be removed before the next stable NixOS that will
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exceed the maintenance period of the kernel version.
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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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## Building a custom kernel {#sec-linux-config-customizing}
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Please refer to the Nixpkgs manual for the various ways of [building a custom kernel](https://nixos.org/nixpkgs/manual#sec-linux-kernel).
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To use your custom kernel package in your NixOS configuration, set
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```nix
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boot.kernelPackages = pkgs.linuxPackagesFor yourCustomKernel;
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```
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## Rust {#sec-linux-rust}
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The Linux kernel does not have Rust language support enabled by
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default. For kernel versions 6.7 or newer, experimental Rust support
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can be enabled. In a NixOS configuration, set:
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```nix
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boot.kernelPatches = [
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{
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name = "Rust Support";
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patch = null;
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features = {
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rust = true;
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};
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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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This section was moved to the [Nixpkgs manual](https://nixos.org/nixpkgs/manual#sec-linux-kernel-developing-modules).
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## ZFS {#sec-linux-zfs}
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It's a common issue that the latest stable version of ZFS doesn't support the latest
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available Linux kernel. It is recommended to use the latest available LTS that's compatible
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with ZFS. Usually this is the default kernel provided by nixpkgs (i.e. `pkgs.linuxPackages`).
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Alternatively, it's possible to pin the system to the latest available kernel
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version _that is supported by ZFS_ like this:
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```nix
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{
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boot.kernelPackages = pkgs.zfs.latestCompatibleLinuxPackages;
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}
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```
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Please note that the version this attribute points to isn't monotonic because the latest kernel
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version only refers to kernel versions supported by the Linux developers. In other words,
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the latest kernel version that ZFS is compatible with may decrease over time.
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An example: the latest version ZFS is compatible with is 5.19 which is a non-longterm version. When 5.19
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is out of maintenance, the latest supported kernel version is 5.15 because it's longterm and the versions
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5.16, 5.17 and 5.18 are already out of maintenance because they're non-longterm.
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