Gave up waiting for root device.common problems
   -Boot args (cat /proc/cmdline) 
   -Check root delay =(did the system wait long enough?) 
   -check root=(did the system wait for right device?)
   -missing modules (cat /proc/module;ls /dev) 
ALERT! /dev/mapper/LTSP--vg-root does not exist.Dropping to shell !
Busy box v1.18.5(ubuntu 1:1.18.5-1 ubuntu 2.1)built in shell /ash)
 Enter help for a list of commands
 (initramfs)