Error after new installation on Mac

[mahesh]

Gave up waiting for root device. Common problems:
— Boot args (cat /proc/cmdline)
— Check rootdelay= (did the system wait long enough?)
— Check root= (did the system wait for the right device?)
— Missing modules (cat /proc/modules; ls /dev)
ALERT! /dev/sda2 does not exist.
Dropping to a shell