pivot_root() does not work in the initramfs. As a fallback, MS_MOVE can be used together with chroot() to mimick pivot_root() somewhat. bubblewrap should use this fallback if pivot_root() is not possible (e.g. when running bubblewrap from the initramfs) so that bubblewrap can be used from the initramfs.

Currently running bubblewrap from the initramfs fails with bwrap: pivot_root: Invalid argument