aarch64 user space on x86_64 Debian/Ubuntu

aarch64-qemu-chroot.sh

# These commands create and enter a aarch64 user space on x86_64 Debian/Ubuntu.
# Expects qemu-aarch64-static to be installed and registered for the aarch64 binfmt on the host, see e.g.: https://codepyre.com/2019/12/arming-yourself/

mkdir -p /tmp/chroot ; mount tmpfs -t tmpfs /tmp/chroot # (tmpfs is optional)
debootstrap --arch=arm64 $(lsb_release --short --codename) /tmp/chroot # install aarch4 user space of host's distro

# copy qemu to where it's registered as binfmt in the kernel (and since it is statically linked, copying a single file is sufficient)
mkdir -p /tmp/chroot/$(dirname $(which qemu-aarch64-static))
cp -a {/,/tmp/chroot/}$(which qemu-aarch64-static)

# make it usable
mkdir -p /tmp/chroot/etc/ ; cp -a {/,/tmp/chroot/}/etc/resolv.conf
for dir in dev/ proc/ sys/ ; do mkdir -p /tmp/chroot/$dir ; mountpoint -q /tmp/chroot/$dir || mount --rbind /$dir /tmp/chroot/$dir ; done

chroot /tmp/chroot /bin/bash --login # do (or rather emulate) great things

mount | grep -oP 'on \K/tmp/chroot(/\S+)?(?=\s)' | xargs -r -n1 umount -l # unmount everything (lazy to avoid "busy" issues, and since it's all virtual file systems anyway)