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Create a busybox initramfs from scratch, and test with qemu

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ntegan/basic_initramfs

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Intro

This repo contains scripting that lays out the process of building an initramfs, kernel, and root filesystem from (pretty much) scratch.

The resulting triplet of (initramfs,kernel,rootfs) is booted using qemu for testing.

Can probably clone and run make all to build the three, and then make run to run in qemu. Tested on archlinux and ubuntu 18.04

Dependencies

  • Docker
  • sudo
  • wget
  • git
  • qemu
  • cpio

base-devel or build-essential

Extra for Ubuntu

  • flex
  • bison
  • libelf-dev

Build a Busybox initramfs

0_build_initramfs.sh contains the implementation of creating an initramfs from a downloaded statically compiled Busybox binary.

https://streamable.com/hfwwgv

Build a root filesystem

1_build_rootfs.sh runs the archlinux docker container in order to create an archlinux base installation/root file system for the initramfs to switch to during the early boot process.

https://streamable.com/sqdnna

Building the linux kernel

2_build_kernel.sh clones Linux from Torvalds' github page, builds a bzImage with defconfig and places it in this repo's output folder.

Note, cloning the whole linux repo takes forever. You can get your own kernel/bzImage and put it in output to skip this step.

https://streamable.com/un4qth

Running the built images

3_run_qemu.sh will boot a qemu/kvm guest in your terminal window and boot into the build initramfs+kernel+rootfs. Login to root user.

Basic networking and editing with vim is available.

https://streamable.com/kluuv0

TODO

setup the archlinux rootfs with locale and such

Might be the reason why can't

man systemd or man systemd.network inside the guest.

Also

can't do this in a chroot, so have to do it once booted in qemu

pacman-key --init
pacman-key --populate

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