grub-install in a new disk /mnt/boot;copy /bin/bash and *.so ; chroot /mnt/sysroot is ok!
use the new disk startup,
"dracut warning can't mount root filesystem
mount :/dev/sda3 already mounted or /sysroot busy
mount: according to mtab, /dev/sdb3 is already mounted on /mnt/sysroot"
don't chroot /mnt/sysroot
startup ——success