[WhyNotHugo]

binfmt can also be used to register qemu for binaries for foreign architectures. This allows running programs compiled for another architecture, and makes it really simply to run podman/docker containers with images for other architectures.

[mamikk]

The qemu and container case is a little interesting because if for example /usr/bin/qemu-system-aarch64 or similar is registered as a binfmt_misc handler for AArch64 ELF binaries; the kernel will execute qemu for AArch64 ELF binaries.

But inside a container (with its own mount namespace) or inside a chroot then the qemu binaries does not necessarily exist. But the binfmt_misc handler will still work in this case because of two features.

1. The kernel will open the qemu binaries in the original mount namespace when the binfmt_misc handler is registered with the F-flag (Fix binary) so the kernel will always have an open file reference to the qemu binary independent of mount namespace.

2. Distributions (at least Debian) ships statically linked qemu binaries so that qemu does not need to load any shared libraries inside the target namespace/chroot.

[nicman23]

also chroot into ie raspi sd cards.