Using systemd-nspawn

This method an easy way to get started with customized images. The systemd-nspawn makes it possible to upgrade the image from the inside using the tools already available in the image.

# Install
apt install systemd-container qemu-user-static

# Unpack rootfs
mkdir rootfs
tar -xJf rootfs.tar.xz -C rootfs

# Start a shell in rootfs using the host network and name resolution
systemd-nspawn -D rootfs --resolv-conf=bind-host

# Work with container filesystem
# e.g. install packages using apt, edit files

# Repack
tar -cJf rootfs.tar.xz -C ./rootfs .

The qemu-user-static package is used to seamlessly emulate arm64 binaries when executing on a x86-64 machine.

Warning

Not everything is guaranteed to work as normal when using qemu-user emulation. Not all system calls are implemented in the emulation layer.