I did an system update on ubuntu server 12.04, which requestet an reboot. Since that, the system never reaches the login. It hangs on:

mount: mounting /dev on /root/dev failed: No such file or directory
done.
mount: mounting /sys on /root/sys failed: No such file or directory
mount: mounting /proc on /root/proc failed: No such file or directory
Target filesystem doesn't have requested /sbin/init.
No init found. Try passing init= bootarg.


BusyBox v1.18.5 (Ubuntu 1:1.18.5-1ubuntu4) build-in shell (ash)
Enter 'help' for a list of build-in commands.

(initramfs)

i tried already to repair it using a live system: + Mounting the filesystems (/boot ext, / btrfs) + fsck ran without problems. + /etc/fstab seems to be OK. + apt update/upgrade on chroot succeed.

now, i have no more ideas :/