How to rescue and re-install Ubuntu after it’s crashed/terminated on upgrading.

1. Using LiveCD to boot the system, or
2. Download Puppy Linux (http://www.puppylinux.com/flash-puppy.htm)
3. Build USB Puppy Linux 

udevadm trigger is not permitted while udev is unconfigured

The solution is to use a live-CD to mount the system (or boot from a completely separate installation), mount the failed OS partition(s), and complete the update process:

Commands listed as below

sudo -i

# create a target mount point
mkdir /mnt/target

# mount root
mount /dev/sda8 /mnt/target (sda8 is the partition Ubuntu exists, using “fdisk -i” to check out the partition. If using putty, it’s easy to check every partition)
# mount boot
mount /dev/sda9 /mnt/target/boot (boot partition, where grub exists. Sometimes, its at the same partition as root)

# into Jaunty
chroot /mnt/target/

# update

sudo apt-get update
dpkg –configure -a

sudo apt-get upgrade

sudo apt-get dist-upgrade

# done

Reboot

exit

#unmount
umount /mnt/target/boot
umount /mnt/target