I have searched a lot,only to found that many people came across this problem. By adding rw init=/bin/bash to the end of the vmlinuz line,I can enter the single-user mode of UBUNTU 10.04 LTS but,when I type shutdown or reboot,it just said it can't do that. Then I run "/sbin/init 0" and it said it can't connect to sock of upstart.
My guess is ,because we replace /sbin/init with /bin/bash and there is no init(nor upstart) thus shutdown can't be done.
I notice that some guy said by enter exit and I should go into next phase of normal boot.I tried that, and the ubuntu system in my VMWare became stuck,and behave weird,at least in the sense of the CAPLOCK light which kept flashing..(CPU occupation scored too)
Any intruction is appreciated,thanks all in advance~
====UPDATED===== I tried single instead of init=/usr/bash but it went straight into multi-user mode.