140 lines
4.2 KiB
Markdown
140 lines
4.2 KiB
Markdown
# Linux Kernel {#sec-kernel-config}
|
|
|
|
You can override the Linux kernel and associated packages using the
|
|
option `boot.kernelPackages`. For instance, this selects the Linux 3.10
|
|
kernel:
|
|
|
|
```nix
|
|
boot.kernelPackages = pkgs.linuxKernel.packages.linux_3_10;
|
|
```
|
|
|
|
Note that this not only replaces the kernel, but also packages that are
|
|
specific to the kernel version, such as the NVIDIA video drivers. This
|
|
ensures that driver packages are consistent with the kernel.
|
|
|
|
While `pkgs.linuxKernel.packages` contains all available kernel packages,
|
|
you may want to use one of the unversioned `pkgs.linuxPackages_*` aliases
|
|
such as `pkgs.linuxPackages_latest`, that are kept up to date with new
|
|
versions.
|
|
|
|
The default Linux kernel configuration should be fine for most users.
|
|
You can see the configuration of your current kernel with the following
|
|
command:
|
|
|
|
```ShellSession
|
|
zcat /proc/config.gz
|
|
```
|
|
|
|
If you want to change the kernel configuration, you can use the
|
|
`packageOverrides` feature (see [](#sec-customising-packages)). For
|
|
instance, to enable support for the kernel debugger KGDB:
|
|
|
|
```nix
|
|
nixpkgs.config.packageOverrides = pkgs: pkgs.lib.recursiveUpdate pkgs {
|
|
linuxKernel.kernels.linux_5_10 = pkgs.linuxKernel.kernels.linux_5_10.override {
|
|
extraConfig = ''
|
|
KGDB y
|
|
'';
|
|
};
|
|
};
|
|
```
|
|
|
|
`extraConfig` takes a list of Linux kernel configuration options, one
|
|
per line. The name of the option should not include the prefix
|
|
`CONFIG_`. The option value is typically `y`, `n` or `m` (to build
|
|
something as a kernel module).
|
|
|
|
Kernel modules for hardware devices are generally loaded automatically
|
|
by `udev`. You can force a module to be loaded via
|
|
[](#opt-boot.kernelModules), e.g.
|
|
|
|
```nix
|
|
boot.kernelModules = [ "fuse" "kvm-intel" "coretemp" ];
|
|
```
|
|
|
|
If the module is required early during the boot (e.g. to mount the root
|
|
file system), you can use [](#opt-boot.initrd.kernelModules):
|
|
|
|
```nix
|
|
boot.initrd.kernelModules = [ "cifs" ];
|
|
```
|
|
|
|
This causes the specified modules and their dependencies to be added to
|
|
the initial ramdisk.
|
|
|
|
Kernel runtime parameters can be set through
|
|
[](#opt-boot.kernel.sysctl), e.g.
|
|
|
|
```nix
|
|
boot.kernel.sysctl."net.ipv4.tcp_keepalive_time" = 120;
|
|
```
|
|
|
|
sets the kernel's TCP keepalive time to 120 seconds. To see the
|
|
available parameters, run `sysctl -a`.
|
|
|
|
## Customize your kernel {#sec-linux-config-customizing}
|
|
|
|
The first step before compiling the kernel is to generate an appropriate
|
|
`.config` configuration. Either you pass your own config via the
|
|
`configfile` setting of `linuxKernel.manualConfig`:
|
|
|
|
```nix
|
|
custom-kernel = let base_kernel = linuxKernel.kernels.linux_4_9;
|
|
in super.linuxKernel.manualConfig {
|
|
inherit (super) stdenv hostPlatform;
|
|
inherit (base_kernel) src;
|
|
version = "${base_kernel.version}-custom";
|
|
|
|
configfile = /home/me/my_kernel_config;
|
|
allowImportFromDerivation = true;
|
|
};
|
|
```
|
|
|
|
You can edit the config with this snippet (by default `make
|
|
menuconfig` won\'t work out of the box on nixos):
|
|
|
|
```ShellSession
|
|
nix-shell -E 'with import <nixpkgs> {}; kernelToOverride.overrideAttrs (o: {nativeBuildInputs=o.nativeBuildInputs ++ [ pkg-config ncurses ];})'
|
|
```
|
|
|
|
or you can let nixpkgs generate the configuration. Nixpkgs generates it
|
|
via answering the interactive kernel utility `make config`. The answers
|
|
depend on parameters passed to
|
|
`pkgs/os-specific/linux/kernel/generic.nix` (which you can influence by
|
|
overriding `extraConfig, autoModules,
|
|
modDirVersion, preferBuiltin, extraConfig`).
|
|
|
|
```nix
|
|
mptcp93.override ({
|
|
name="mptcp-local";
|
|
|
|
ignoreConfigErrors = true;
|
|
autoModules = false;
|
|
kernelPreferBuiltin = true;
|
|
|
|
enableParallelBuilding = true;
|
|
|
|
extraConfig = ''
|
|
DEBUG_KERNEL y
|
|
FRAME_POINTER y
|
|
KGDB y
|
|
KGDB_SERIAL_CONSOLE y
|
|
DEBUG_INFO y
|
|
'';
|
|
});
|
|
```
|
|
|
|
## Developing kernel modules {#sec-linux-config-developing-modules}
|
|
|
|
When developing kernel modules it\'s often convenient to run
|
|
edit-compile-run loop as quickly as possible. See below snippet as an
|
|
example of developing `mellanox` drivers.
|
|
|
|
```ShellSession
|
|
$ nix-build '<nixpkgs>' -A linuxPackages.kernel.dev
|
|
$ nix-shell '<nixpkgs>' -A linuxPackages.kernel
|
|
$ unpackPhase
|
|
$ cd linux-*
|
|
$ make -C $dev/lib/modules/*/build M=$(pwd)/drivers/net/ethernet/mellanox modules
|
|
# insmod ./drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.ko
|
|
```
|