ubuntu 12.04 does not detect already installed windows 7

Question

I have already installed windows 7 ultimate. When i tried to install ubuntu 12.04, installer didn't detect windows even i have only two primary and two logical partition on windows when i goes through try ubuntu and use command " os-prober" it shows output like as

 unshare failed: Operation not permitted
ERROR: you must be root
ERROR: you must be root
ERROR: you must be root
ERROR: you must be root
ERROR: you must be root
ERROR: you must be root
mkdir: cannot create directory `/var/lib/os-prober/mount': Permission denied
mkdir: cannot create directory `/var/lib/os-prober/mount': Permission denied
mkdir: cannot create directory `/var/lib/os-prober/mount': Permission denied
mkdir: cannot create directory `/var/lib/os-prober/mount': Permission denied
mkdir: cannot create directory `/var/lib/os-prober/mount': Permission denied"

Please help me. What should I do?

Answer 1

sudo os-prober, but maybe sudo update-grub(2)