It's 2024 2025 and floppies are still cool. Maintain that coolness by building your own floppy-sized Linux distro like it's 1999.
This project is buildable by a gcc toolchain provided by your distribution or by building a musl toolchain. For the smallest binaries sizes, musl is recommended.
Two pre-built bootable floppy images are available in Releases:
- Linux 6.12.9: Latest kernel build
qemu-system-i386 -fda fluxflop-linux-6.12.9-boot.img -boot a -m 32- Linux 4.20.17: Optimized for real i486DX hardware
- Minimum requirements:
- i486DX CPU @ 25MHz+ (SX models not supported)
- 8MB RAM minimum (16MB recommended)
- Boots from:
- Real 1.44MB floppy disk
- 86Box/PCem with i486DX configuration
- QEMU with 5-32MB RAM setting
gcc-i686 build:
Packages:
apt-get install build-essential gcc-i686-linux-gnu g++-i686-linux-gnu i486/i686-musl build:
# see README.md within musl-cross-make for all targets git clone https://github.com/richfelker/musl-cross-make cd musl-cross-make make TARGET=i486-linux-musl make install arm64-musl build:
make TARGET=aarch64-linux-musl make install Add the musl toolchain to your path: export PATH=~/musl-cross-make/output/bin:$PATH
Building on Mac OS:
Save yourself a headache and use a pre-built toolchain courtesy of homebrew-macos-cross-toolchains
brew tap messense/macos-cross-toolchains # valid targets are aarch64-unknown-linux-musl, arm-unknown-linux-musleabihf # armv7-unknown-linux-musleabihf, i686-unknown-linux-musl, x86_64-unknown-linux-musl brew install i686-unknown-linux-musl Install the LLVM linker:
brew install lld Install lkmake to included needed headers files for a successful build:
brew tap markbhasawut/markbhasawut brew -v install markbhasawut/markbhasawut/mac-linux-kdk For the following directions, use lkmake in place of make
Create a build dir: mkdir build/
Prepare the kernel:
cd build/ wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.9.3.tar.xz tar -xf linux-6.9.3.tar.xz # see configs/linux for all configs available # .config - default i686 config # .config-x86-fb - i486 with framebuffer support # .config-x86-serial - i486 with serial support # .config-x86-vga - i486(DX) with VGA cp ./configs/linux/6.x.x/.config-<config-name> linux-6.9.3/.config The smallest kernel produced is using .config-x86-fb (XZ compression) = 592KB
Root filesystem layout:
mkdir -p root/{bin,proc,dev,sys,usr} # Create a simple init script # or compile tools/init.c and place in root/ cat > root/init <<EOF #!/bin/sh # Mount essential filesystems mount -t proc none /proc mount -t sysfs none /sys mount -t devtmpfs none /dev # Start a shell exec /bin/sh -i # Infinite loop to prevent the script from exiting while true; do sleep 1 done EOF chmod a+x root/init # you will need root privileges to make these nodes mknod -m 660 ./root/dev/console c 5 1 mknod -m 666 ./root/dev/ttyS0 c 4 64 mknod -m 666 ./root/dev/tty c 5 0 Output image directories:
mkdir -p bootable_image/{boot,isolinux} Linux: Note: if you are including the initramfs in .config within the built image, build the rootfs first.
cd linux-6.9.3 make ARCH=x86 CROSS_COMPILE=i686-linux-gnu- -j8 #use bzImage for x86, Image.gz for arm64. adjust -gnu to -musl as needed Toybox:
wget https://landley.net/toybox/bin/toybox-i486 -O ./root/bin/toybox-i486 ./scripts/toybox-symlinks.sh Toybox provides many common Linux utilities including a shell. For the sake of simplicity, the static builds provided by Toybox is used. You can optionally compile Toybox yourself:
cd build/ wget https://landley.net/toybox/downloads/toybox-0.8.11.tar.gz tar xvf toybox-0.8.11.tar.gz cp ../configs/toybox/.config toybox-0.8.11 cd toybox-0.8.11 make CFLAGS="-march=i486 -mtune=i486" LDFLAGS="-static -s" ARCH=x86 CROSS_COMPILE=i486-linux-musl- -j8 make install cp -R install/* ./root Strip debug symbols in the root filesystem:
./scripts/stripfs.sh Make the initramfs:
./scripts/make-cpio.sh (Optional): Syslinux for ISOs:
wget https://mirrors.edge.kernel.org/pub/linux/utils/boot/syslinux/syslinux-6.03.tar.gz tar xvf syslinux-6.03.tar.gz cd syslinux-6.03 cp syslinux/bios/core/isolinux.bin bootable_image/isolinux cp syslinux/bios/com32/elflink/ldlinux/ldlinux.c32 bootable_image/isolinux # copy config cp configs/isolinux/isolinux.cfg bootable_image/isolinux Make a bootable ISO:
./scripts/make-iso.sh and boot with:
qemu-system-i386 -cdrom out.iso -m 32 -nographic Make a bootable floppy: If not already set, edit the Linux .config and set CONFIG_INITRAMFS_SOURCE to your rootfs cpio archive path.
cd build/ git clone https://github.com/oerg866/w98qi-tiny-floppy-bootloader cd w98qi-tiny-floppy-bootloader/ # generate a bootable floppy bash build.sh ../linux-6.9.3/arch/x86/boot/bzImage disk.img Boot with qemu: qemu-system-i386 -fda disk.img
Boot with kernel and initial ramdisk with qemu:
qemu-system-i386 -kernel ./linux-6.8.11/arch/x86/boot/bzImage -initrd ./rootfs.cpio.gz -append "init=/init rdinit=/init console=ttyS0,115200n8" -m 32 -nographic or, if you built with simple framebuffer:
qemu-system-i386 -kernel ./bzImage -initrd ./rootfs.cpio.gz -append "init=/init rdinit=/init console=tty0" -m 32 Use a simple C program to use as init:
gcc -static -o init tools/init.c Use as the initramfs:
echo init | cpio -ov --format=newc > initramfs.img Kernel image comparison with printk support:
with:
stat -c %s arch/arm64/boot/Image 2809864 without:
stat -c %s arch/arm64/boot/Image 2283528 -fomit-frame-pointer:
easto@debian-build:~/testing-linux/linux-6.8.11$ ls -ls arch/x86/boot/bzImage 728 -rw-r--r-- 1 easto easto 741888 May 30 02:27 arch/x86/boot/bzImage easto@debian2:/tmp/linux-6.9.3$ stat -c %s vmlinux 1919144 make KCFLAGS="-fomit-frame-pointer" ARCH=x86 CROSS_COMPILE=i686-linux-gnu- bzImage -j8 easto@debian-build:~/testing-linux/linux-6.8.11$ ls -ls arch/x86/boot/bzImage 716 -rw-r--r-- 1 easto easto 729600 May 30 02:30 arch/x86/boot/bzImage easto@debian2:/tmp/linux-6.9.3$ stat -c %s vmlinux 1886332 -fno-inline-small-functions:
easto@debian2:/tmp/linux-6.9.3$ stat -c %s vmlinux 1919144 make KCFLAGS="-fno-inline-small-functions" ARCH=x86 CROSS_COMPILE=i486-linux-musl- -j8 easto@debian2:/tmp/linux-6.9.3$ stat -c %s vmlinux 1919528 find largest objects:
nm --size-sort --print-size vmlinux | tail -n 20 or using Bloaty
bloaty -d symbols -n 100 vmlinux https://justine.lol/sizetricks/
https://elinux.org/images/7/72/Linux_tiny.pdf
https://git.openembedded.org/meta-micro/tree/conf
https://ops.tips/notes/booting-linux-on-qemu/
https://github.com/ahgamut/superconfigure/?tab=readme-ov-file
https://github.com/buildroot/buildroot/tree/master/board/qemu/aarch64-virt