funtoo-ramdisk 1.0.2

Funtoo framework for creating initial ramdisks.

Copyright 2023 Daniel Robbins, Funtoo Solutions, Inc.

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Introduction

The Funtoo ramdisk tool, called ramdisk is a stand-alone tool to create an initial RAM disk filesystem (initramfs) for booting your Linux system.

The internal initramfs logic is based on the logic found in Gentoo Linux’s genkernel tool, but has been rewritten to be simpler and more efficient.

You can use this tool to create an initramfs to boot to a Funtoo Linux root ext4 or XFS filesystem, which is what we support in our official installation documentation at https://www.funtoo.org/Install – but that’s about it.

What’s Not Included

Nearly all “extra” genkernel features are intentionally not yet implemented. This tool doesn’t build your kernel or modules.

It also currently doesn’t support dmraid, zfs, btrfs, encrypted root, or LiveCD or LiveUSB booting.

Why not? Because one of the main design goals of this project is to create a very elegant and easy-to-understand initramfs whose core logic is not cluttered with tons of questionable features. To start from a clean slate, we are starting from very minimal functionality and then will very carefully add back various features while keeping the code clean, simple, elegant and effective.

What’s Included

So, what does Funtoo’s ramdisk tool actually offer? Here’s a list:

• genkernel-style initramfs without the cruft. In comparison to genkernel’s initramfs, the shell code is about 10x simpler and a lot cleaner, but does the same thing and has been modernized. About 150 lines of bash shell, with another 150 lines of functions.

• Rootless operation. You do not need enhanced privileges to create the initramfs.

• You can read the linuxrc script and actually understand what it does. It is written to be easy to understand and adapt. So it’s not just short, but easy to grasp.

• Enhanced module loading engine on the initramfs which is significantly faster than genkernel. This effectively eliminates the “watching the stream of useless modules being loaded” issue with genkernel. Modern systems with NVMe drives will load just a handful of modules to boot – all without requiring any special action from the user.

• If you are still able to find some modules that got loaded that you don’t want loaded, you can use the “magic modules” feature to specify just the modules you want to load. Specify magic=mod1,mod2,mod3 as a kernel argument and just these modules will be loaded.

• Effective Python-based command to actually build the ramdisk, which is called: ramdisk. This gives us an extensible platform for the future.

• Enhanced ini-style system for selecting modules to include on your initramfs.

• Enhanced ini-style system for selecting module groups to autoload on the initramfs.

• Support for xz and zstd compression.

How To Use It

First, install the package, via emerge ramdisk on Funtoo Linux, or alternatively pip3 install --user funtoo-ramdisk. You will then have a ramdisk command in your path, which can be used to build a ramdisk.

Then, as a regular user, you can run:

ramdisk /var/tmp/my-new-initramfs
sudo cp /var/tmp/my-new-initramfs /boot

By default, ramdisk will use your /usr/src/linux symlink to determine which kernel to use to build a ramdisk for. It will parse /usr/src/linux/Makefile, extract kernel version information, and then find the appropriate directory in /lib/modules/<kernel_name> for copying modules.

Since this is brand-new software, it is highly recommended that you DO NOT OVERWRITE YOUR EXISTING, WORKING INITRAMFS THAT YOU CURRENTLY USE TO BOOT YOUR SYSTEM.

Instead – create a NEW BOOT ENTRY to test your initramfs. In GRUB, you can also press ‘e’ to edit an entry and type in the name of the new initramfs to give it a try.

Enjoy – and let me know how it works for you! Please report issues and feature requests to https://bugs.funtoo.org.