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mksquashfs ubuntu_root/ ubuntu.squashfs -comp xz -Xdict-size 1M -b 1M The Ultimate Packer for Executables (UPX) can shrink individual binaries by 50-70%.
# Install required tools on Ubuntu sudo apt install build-essential libncurses-dev busbox-static git clone https://github.com/tinycore/linux-kernel-config make tinyconfig # Enable only essential drivers Build kernel make -j$(nproc) Result: bzImage ~ 6MB Create initrd with BusyBox mkdir initrd cd initrd cp /bin/busybox ./bin/ ln -s busybox ./bin/sh echo '#!/bin/sh' > init echo 'mount -t proc none /proc' >> init echo 'exec /bin/sh' >> init chmod +x init find . | cpio -o -H newc | xz --extreme > ../initrd.xz Result: initrd.xz ~ 3.5MB ubuntu highly compressed 10mb
This boots into a root shell where you can run apt (if you add network modules). It’s not a full Ubuntu, but it’s Ubuntu-compatible at the kernel level. Ubuntu Core is a snap-only version of Ubuntu for IoT. A compressed image of the minimal "gadget" snap can be as low as 15-20MB – tantalizingly close. However, it expands to ~200MB on installation. mksquashfs ubuntu_root/ ubuntu
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