Help! /bin/bash not found on chroot

[Volker Wysk]

Hello!

Something happened to my system. Suddenly, next to nothing worked any
more. For instance "ls" won't be found any longer.

I made a reboot and the system asks for the disk password, and
afterwards dies. When going into the recovery, then there are messages
stating that /sbin/init and /etc/init aren't found. Then the system
stops with a kernel panic.

I'm trying to fix the problem by booting from an USB stick. Then I
mount the faulty system at /mnt/rootneu and do this:

mount BOOTPART /mnt/rootneu/boot
mount EFIPART /mnt/rootneu/boot/efi
mount --rbind /dev /mnt/rootneu/dev
mount --rbind /proc /mnt/rootneu/proc
mount --rbind /sys /mnt/rootneu/sys

I do this so I can "update-initramfs -u", "grub-install ..." and
"update-grub" later.

So far, it works. But then I try to chroot to the system that fails
with:

chroot /mnt/rootneu

This FAILS with:

chroot: failed to run command '/bin/bash': No such file or directory

Even though /bin/bash and /mnt/rootneu/bin/bash are both present and
can be started.

So here I'm in need for help. Why doesn't chroot work?

It's a Ubunut 20.04.3 LTS system.

Thanks in advance,
Volker