> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ryoku.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Kernels

> Ryoku boots the stock Arch kernel and can add the CachyOS kernel as an opt-in from Extras, with the stock kernel kept as a fallback.

Ryoku ships and boots the stock Arch `linux` kernel. The Hub's **Extras** section
can add the CachyOS kernel (`linux-cachyos`) as an opt-in alternative. This page
is what to weigh before flipping it, what it does and does not change, and how to
back out. Your stock kernel is never removed, so this is a low-risk toggle.

## Should you switch?

<Tabs>
  <Tab title="Pros">
    * An optimized, patched build: Clang ThinLTO and AutoFDO, an x86-64-v3
      target, and the Cachy patchset.
    * The mainline EEVDF scheduler with `sched-ext` compiled in, so you can opt
      into a latency or gaming scheduler (`scx_lavd` and friends) via
      `scx-scheds`.
    * A modest, workload-dependent throughput edge on CPU-bound work, plus
      steadier behaviour under load.
  </Tab>

  <Tab title="Cons">
    * Pulls in the CachyOS repository and signing key, so kernel updates now
      depend on one more upstream being healthy.
    * Every DKMS module (NVIDIA, VirtualBox, and the like) rebuilds against the
      new kernel. A failed rebuild means that module is missing on that kernel
      until it is fixed.
    * Tracks mainline more aggressively than Arch's `linux`, so marginally more
      churn.
  </Tab>
</Tabs>

The gain is real for gamers and heavy multitaskers; a light desktop will barely
notice it. Whatever you decide, your stock Arch kernel stays installed and
remains the safe fallback you can always boot.

<Warning>
  The CachyOS kernel requires a CPU that supports **x86-64-v3** (essentially
  every CPU since roughly 2015). The installer refuses to add the repo on a CPU
  that does not.
</Warning>

## Enable it

<Steps>
  <Step title="Open Extras">
    Ryoku Settings (`Mod+,`) > **Store / Extras**, then find **CachyOS Kernel**.
  </Step>

  <Step title="Install the bundle">
    Install it like any other Extras bundle. Under the hood the Hub runs
    `ryoku-extras-install`, which adds the `[cachyos-v3]` repository (signing the
    CachyOS key and inserting the repo above `[core]`) and installs
    `linux-cachyos` and `linux-cachyos-headers`.
  </Step>

  <Step title="Reboot">
    A reboot is required to actually run the new kernel. On a Ryoku install the
    Limine boot entries regenerate automatically when the kernel package lands,
    so `linux-cachyos` appears in the boot menu and the stock kernel stays the
    default.
  </Step>
</Steps>

Prefer the terminal? `ryoku-extras-install install bundle cachyos-kernel` does
the same thing. See [Extras](/docs/extras) for how bundles work.

<Warning>
  Installing the kernel rebuilds every DKMS module against it, so watch for
  NVIDIA build errors during the transaction. `/boot` also gains a second kernel
  image and initramfs, so it uses more space.
</Warning>

## What changes, and what doesn't

Ryoku adds **only** the `[cachyos-v3]` repository and installs the kernel. That
repo holds CachyOS's own packages rather than rebuilds of Arch's `core` and
`extra`, so the kernel is the only thing sourced from CachyOS. Deliberately left
out:

* The baseline `[cachyos]` repo (which ships CachyOS's forked pacman).
* The `cachyos-core-v3` / `cachyos-extra-v3` userland rebuilds.

That means a later `pacman -Syu` cannot quietly replace your userland or your
package manager. Your desktop, defaults, apps, and the `[ryoku]` repo are exactly
as before; you have simply borrowed a kernel. Kernel updates flow through the
normal [`ryoku update`](/docs/updates) run, snapshots and all.

## Is it still Ryoku?

Yes. A distribution is defined by its desktop, tooling, repository, and defaults,
not by which kernel it boots. Installing `linux-cachyos` is the same kind of
choice as `linux-zen` or `linux-lts`: one swappable component. The system stays
Ryoku, on the Arch base, with the `[ryoku]` desktop, the `ryoku` CLI, and the
same opinionated defaults. `/etc/os-release` still reads exactly as before.

Opinionated does not mean fixed. The Ryoku *default* is opinionated: a fresh
install boots the stock Arch kernel, and that choice is ours to make. The CachyOS
kernel is an explicit opt-in, never the default. Offering the toggle does not
dilute the default install; it hands a power user one clearly labelled lever and
leaves everyone else exactly where they were.

<Note>
  This is not a full CachyOS install. CachyOS's own ISO gives you their entire
  optimized userland, their pacman fork, and their branding, a CachyOS system,
  not Ryoku's shell and Hub. The toggle exists so you can get the kernel's
  benefit without giving up the thing that makes the machine Ryoku.
</Note>

## Rollback

Rollback is built in and cheap:

* **Just boot the stock kernel.** The stock Arch kernel is never removed. If the
  CachyOS kernel misbehaves, pick the stock entry at the Limine menu and you are
  back. There is nothing to undo.
* **Recover the whole transaction.** Installing the kernel is a pacman
  transaction, so snapper and snap-pac take a pre/post snapshot pair and
  limine-snapper-sync exposes them in the boot menu; a whole bad transaction is
  recoverable from the boot screen. See [Updates](/docs/updates).
* **Remove it outright.** In Ryoku Settings > Extras > **CachyOS Kernel**, choose
  remove, or run `ryoku-pkg-remove linux-cachyos linux-cachyos-headers`. The
  `[cachyos-v3]` repo line is left in place; it is inert with no CachyOS packages
  installed, so delete it by hand only if you want a spotless `pacman.conf`.

## See also

<CardGroup cols={2}>
  <Card title="Extras" icon="box-open" href="/docs/extras">
    How the Extras bundles install, update, and remove software.
  </Card>

  <Card title="Updates" icon="arrows-rotate" href="/docs/updates">
    Snapshots, the boot-menu recovery path, and how updates stay reversible.
  </Card>
</CardGroup>