refactor: move nixos-manual to reference/ + graphifyignore

reference/nixos-manual/configuration/linux-kernel.chapter.md

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+# 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.
+
+Please note that the current convention in NixOS is to only keep actively
+maintained kernel versions on both unstable and the currently supported stable
+release(s) of NixOS. This means that a non-longterm kernel will be removed after it's
+abandoned by the kernel developers, even on stable NixOS versions. If you
+pin your kernel onto a non-longterm version, expect your evaluation to fail as
+soon as the version is out of maintenance.
+
+A kernel will be removed from nixpkgs when the first batch of stable kernels
+_after_ the final release is published. E.g. when 6.15.11 is the final release
+of the 6.15 series and is released together with 6.16.3 and 6.12.43, it will be
+removed on the release of 6.16.4 and 6.12.44. Custom kernel variants such
+as linux-hardened are also affected by this.
+
+Longterm versions of kernels will be removed before the next stable NixOS that will
+exceed the maintenance period of the kernel version.
+
+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`.
+
+## Building a custom kernel {#sec-linux-config-customizing}
+
+Please refer to the Nixpkgs manual for the various ways of [building a custom kernel](https://nixos.org/nixpkgs/manual#sec-linux-kernel).
+
+To use your custom kernel package in your NixOS configuration, set
+
+```nix
+{ boot.kernelPackages = pkgs.linuxPackagesFor yourCustomKernel; }
+```
+
+## Rust {#sec-linux-rust}
+
+The Linux kernel does not have Rust language support enabled by
+default. For kernel versions 6.7 or newer, experimental Rust support
+can be enabled. In a NixOS configuration, set:
+
+```nix
+{
+  boot.kernelPatches = [
+    {
+      name = "Rust Support";
+      patch = null;
+      features = {
+        rust = true;
+      };
+    }
+  ];
+}
+```
+
+## Developing kernel modules {#sec-linux-config-developing-modules}
+
+This section was moved to the [Nixpkgs manual](https://nixos.org/nixpkgs/manual#sec-linux-kernel-developing-modules).
+
+## ZFS {#sec-linux-zfs}
+
+It's a common issue that the latest stable version of ZFS doesn't support the latest
+available Linux kernel. It is recommended to use the latest available LTS that's compatible
+with ZFS. Usually this is the default kernel provided by nixpkgs (i.e. `pkgs.linuxPackages`).