An Embedded 🐧Linux on a Single 💾Floppy

2025 Edition (v0.3.1)

FLOPPINUX was released in 2021. After four years people find it
helpful. Because of that I decided to revisit FLOPPINUX in 2025 and make
updated tutorial. This brings bunch of updates like latest kernel and
persistent storage.

Table of Contents

• Main Project Goals
• Linux Kernel
• 64-bit Base OS
• Working Directory
• System Requirements
• Kernel
• Toolset
• Filesystem
• Boot Image
• Floppy Disk
• Summary
• Download

Main Project Goals

Think of this as Linux From Scratch but for making single floppy
distribution.

It is meant to be a full workshop (tutorial) that you can follow
easily and modify it to your needs. It is a learning exercise. Some base
Linux knowledge is needed.

The final distribution is very simple and consists only of minimum of
tools and hardware support. As a user you will be able to boot any PC
with a floppy drive to a Linux terminal, edit files, and create simple
scripts. There is 264KB of space left for your newly created files.

Core features:

• Fully working distribution booting from the single floppy
• Latest* Linux kernel
• Supporting all 32-bit x86 CPUs since Intel 486DX
• Have a working text editor (Vi) and basic file manipulation commands
  (move, rename, delete, etc.)
• Support for simple scripting
• Persistent storage on the floppy to actualy save files (264KB)
• Works on real hardware and emulation

Minimum Hardware
Requirements:

• Intel 486DX 33MHz
• 20MB RAM
• Internal floppy disk

Linux Kernel

The Linux kernel drops i486 support in 6.15 (released May 2025), so
6.14 (released March 2025) is the latest version with
full compatibility.

64-bit Base OS

This time I will do everything on Omarchy Linux. It
is 64-bit operating system based on Arch Linux. Instructions should work
on all POSIX systems. Only difference is getting needed packages.

Working Directory

Create directory where you will keep all the files.

mkdir ~/my-linux-distro/
BASE=~/my-linux-distro/
cd $BASE

Host OS Requirements

You need supporting software to build things. This exact list may
vary depending on the system you have.

Install needed software/libs. On Arch/Omarchy 3.1:

sudo pacman -S ncurses bc flex bison syslinux cpio

Cross-compiler:

wget https://musl.cc/i486-linux-musl-cross.tgz
tar xvf i486-linux-musl-cross.tgz
rm i486-linux-musl-cross.tgz

Emulation

86Box is also good but slower. Bochs is the best but for debugging,
not needed here.

For emulation I will be using qemu.

Kernel

Get the sources for the latest compatible kernel
6.14.11:

git clone --depth=1 --branch v6.14.11 https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
cd linux

Now, that you have them in linux/ directory lets
configure and build our custom kernel. First create tiniest base
configuration:

This is a bootstrap with absolute minimum features. Just enough to
boot the system. We want a little bit more.

Add additonal config settings on top of it:

Important: Do not uncheck anything in options unless specified so.
Some of those options are important. You can uncheck but on your own
risk.

From menus choose those options:

• General Setup
  • Configure standard kernel features (expert users)
    • Enable support for printk
  • Initial RAM filesystem and RAM disk (initramfs/initrd)
    • Support initial ramdisk/ramfs compressed using XZ and
      uncheck everything else
• Processor type and features
  • x86 CPU resources control support
  • Processor family
    • 486DX
• Enable the block layer
• Executable file formats
  • Kernel support for ELF binaries
  • Kernel support for scripts starting with #!
• Device Drivers
  • Block devices
    • Normal floppydisk support
    • RAM block device support
      • Default number of RAM disk: 1
  • Character devices
    • Enable TTY
• File systems
  • DOS/FAT/EXFAT/NT Filesystems
    • MSDOS fs support
  • Pseudo filesystems
    • /proc file system support
    • sysfs file system support
  • Native language support
    • Codepage 437
• Library routines
  • XZ decompression and uncheck everything under
    it

Exit configuration (yes, save settings to .config).

Time for compiling!

Compile Kernel

make ARCH=x86 bzImage -j$(nproc)

This will take a while depending on the speed of your CPU. In the end
the kernel will be created in arch/x86/boot/ as
bzImage file.

Move kernel to our main directory and go
back to it:

mv arch/x86/boot/bzImage ../
cd ..

Without tools kernel will just boot and you will not be able to do
anything. One of the most popular lightweight tools is BusyBox. It
replaces the standard GNU utilities with way smaller but still
functional alternatives, perfect for embedded needs.

Get the 1.36.1 version from busybox.net or Github
mirror. Download the file, extract it, and change directory:

Remember to be in the working directory.

wget https://github.com/mirror/busybox/archive/refs/tags/1_36_1.tar.gz
tar xzvf 1_36_1.tar.gz
rm 1_36_1.tar.gz
cd busybox-1_36_1/

As with kernel you need to create starting configuration:

make ARCH=x86 allnoconfig

You may skip this following fix if you are building on
Debian/Fedora

Fix for Arch Linux based distributions:

sed -i 's/main() {}/int main() {}/' scripts/kconfig/lxdialog/check-lxdialog.sh

Now the fun part. You need to choose what tools you
want. Each menu entry will show how much more KB will be taken
if you choose it. So choose it wisely 🙂 For the first time use my
selection.

Run the configurator:

Choose the following options. Remember to do not
uncheck anything if not stated here.

• Settings
  • Support files
    • 2GB
  • Build static binary (no shared libs)
• Coreutils
  • cat
  • cp
  • df
  • echo
  • ls
  • mkdir
  • mv
  • rm
  • sync
  • test
    • test as [
    • test as [[
• Console Utilities
  • clear
• Editors
  • vi
• Init Utilities
  • init
    • uncheck everything else (inside init: keep [*] only
      on init in this page)
• Linux System Utilities
  • mdev
  • mount
    • Support lots of -o flags
    • uncheck evrything else
  • umount
• Miscellaneous Utilities
  • uncheck readahead
• Shells
  • Choose alias as (ash)
  • ash
  • Optimize for size instead of speed
  • Alias support

Now exit with save config.

Cross Compiler Setup

Our target system needs to be 32-bit. To compile it on 64-bit system
we need a cross compiler. You can setup this by hand in the menuconfig
or just copy and paste those four lines.

Setup paths:

sed -i "s|.*CONFIG_CROSS_COMPILER_PREFIX.*|CONFIG_CROSS_COMPILER_PREFIX="${BASE}/i486-linux-musl-cross/bin/i486-linux-musl-"|" .config

sed -i "s|.*CONFIG_SYSROOT.*|CONFIG_SYSROOT="${BASE}/i486-linux-musl-cross"|" .config

sed -i "s|.*CONFIG_EXTRA_CFLAGS.*|CONFIG_EXTRA_CFLAGS=-I$BASE/i486-linux-musl-cross/include|" .config

sed -i "s|.*CONFIG_EXTRA_LDFLAGS.*|CONFIG_EXTRA_LDFLAGS=-L$BASE/i486-linux-musl-cross/lib|" .config

Compile BusyBox

Build tools and create base filesystem (“install”). It will ask for
options, just press enter for default for all of
them.

make ARCH=x86 -j$(nproc) && make ARCH=x86 install

This will create a filesystem with all the files at **_install/**.
Move it to our main directory. I like to rename it to.

Lastly to to that new directory.

mv _install ../filesystem
cd ../filesystem

Filesystem

You got kernel and basic tools but the system still needs some
additional directory structure.

This created minimum viable directory structure for satisfying the
basic requirements of a Linux system.

Remember to be in the filesystem/ directory.

mkdir -pv {dev,proc,etc/init.d,sys,tmp,home}
sudo mknod dev/console c 5 1
sudo mknod dev/null c 1 3

Next step is to add minimum configuration files. First one is a
welcome message that will be shown after booting.

Here is the first real opportunity to go wild and make this your own
signature.

cat >> welcome << EOF
Your welome message or ASCII art.
EOF

Or download my welcome file.

wget https://krzysztofjankowski.com/floppinux/downloads/0.3.1/welcome

It looks like that:

$ cat welcome

                _________________
               /_/ FLOPPINUX  /_/;
              / ' boot disk  ' //
             / '------------' //
            /   .--------.   //
           /   /         /  //
          .___/_________/__//   1440KiB
          '===_________=='   3.5"

_______FLOPPINUX_V_0.3.1 __________________________________
_______AN_EMBEDDED_SINGLE_FLOPPY_LINUX_DISTRIBUTION _______
_______BY_KRZYSZTOF_KRYSTIAN_JANKOWSKI ____________________
_______2025.12 ____________________________________________

Back to serious stuff. Inittab tells the system what to do in
critical states like starting, exiting and restarting. It points to the
initialization script rc that is the first thing that our OS will run
before dropping into the shell.

Create an inittab file:

cat >> etc/inittab << EOF
::sysinit:/etc/init.d/rc
::askfirst:/bin/sh
::restart:/sbin/init
::ctrlaltdel:/sbin/reboot
::shutdown:/bin/umount -a -r
EOF

And the init rc script:

cat >> etc/init.d/rc << EOF
#!/bin/sh
mount -t proc none /proc
mount -t sysfs none /sys
mdev -s
ln -s /proc/mounts /etc/mtab
mkdir -p /mnt /home
mount -t msdos -o rw /dev/fd0 /mnt
mkdir -p /mnt/data
mount --bind /mnt/data /home
clear
cat welcome
cd /home
/bin/sh
EOF

Make the script executable and owner of all files to root:

chmod +x etc/init.d/rc
sudo chown -R root:root .

Compress this directory into one file. Then go back to working
directory.

find . | cpio -H newc -o | xz --check=crc32 --lzma2=dict=512KiB -e > ../rootfs.cpio.xz
cd ..

Create booting configuration.

Another place to tweak parameters for your variant. Text after SAY is
what will be displayed on the screen as first, usualy a name of the
OS.

The tsc=unstable is useful on some (real) computers to get rid of
randomly shown warnings about Time Stamp Counter.

Remember to be in the working directory.

cat >> syslinux.cfg << EOF
DEFAULT floppinux
LABEL floppinux
SAY [ BOOTING FLOPPINUX VERSION 0.3.1 ]
KERNEL bzImage
INITRD rootfs.cpio.xz
APPEND root=/dev/ram rdinit=/etc/init.d/rc console=tty0 tsc=unstable
EOF

Make it executable:

Create sample file

To make the system a little bit more user friendly I like to have a
sample file that user will be able to read and edit. You can put
anything you want in it. A simple help would be also a good idea to
include.

cat >> hello.txt << EOF
Hello, FLOPPINUX user!
EOF

Filesystem is ready. Final step is to put this all on a
floppy!

Boot Image

First we need an empty file in exact size of a floppy disk. Then
format and make it bootable.

Create empty floppy image:

dd if=/dev/zero of=floppinux.img bs=1k count=1440

Format it and create bootloader:

mkdosfs -n FLOPPINUX floppinux.img
syslinux --install floppinux.img

Mount it and copy syslinux, kernel, and filesystem onto it:

sudo mount -o loop floppinux.img /mnt
sudo mkdir /mnt/data
sudo cp hello.txt /mnt/data/
sudo cp bzImage /mnt
sudo cp rootfs.cpio.xz /mnt
sudo cp syslinux.cfg /mnt
sudo umount /mnt

Done!

Test in emulator

It’s good to test before wasting time for the real floppy to
burn.

Boot the new OS in qemu:

qemu-system-i386 -fda floppinux.img -m 20M -cpu 486

If it worked that means You have successfully created your own
distribution! Congratulations!

The floppinux.img image is ready to burn onto a
floppy and boot on real hardware!

Floppy Disk

Important

Change XXX to floppy drive name in your system. In my case it is
sdb. Choosing wrongly will NUKE YOUR PARTITION and
REMOVE all of your files! Think twice. Or use some GUI application for
that.

sudo dd if=floppinux.img of=/dev/XXX bs=512 conv=notrunc,sync,fsync oflag=direct status=progress

After 5 minutes I got freshly burned floppy.

Summary

• FLOPPINUX: 0.3.1 (December 2025)
• Linux Kernel: 6.14.11
• Busybox: 1.36.1
• Image size: 1440KiB / 1.44MiB
• Kernel size: 881KiB (bzImage)
• Tools: 137KiB (rootfs.cpio.xz)
• Free space left (df -h): 253KiB

System Tools

File & Directory
Manipulation

• cat – display file contents
• cp – copy files and directories
• mv – move/rename files and directories
• rm – remove files and directories
• ls – list directory contents
• mkdir – creates directory

System Information &
Management

• df -h – display filesystem disk space usage
• sync – force write of buffered data to disk – use this
  after any changes to the floppy filesystem
• mount – mount filesystems
• umount – unmount filesystems

Text Processing & Output

• echo – display text output
• more – page through text output

Utilities

• clear – clear terminal screen
• test – evaluate conditional expressions

Applications

• vi – text editor

Download

• FLOPPINUX
  0.3.1 Floppy Image 1.44MB