Can't mount root fs(Linux OS)

When you boot a system, this is an error that will halt the system. This error means that the kernel can't
mount the root file system, so it can't get all of its configuration files.
There are a few cases where this happens:
·  No IDE support in the kernel. If your main hard drive is an IDE, and you have recompiled
without including "Enhanced IDE/MFM/RLL disk/cdrom/tape/floppy support" or some other
basic IDE device drivers.
·  File system not supported. Usually the root file system should be of type ext2. You need to
make sure that ext2 is compiled in the kernel, and not as a module because you can't load
modules without first mounting the root file system.
·  The drive is not ready. If you have removed the drive, the hard disk died or the BIOS didn't
detect the device for some reason, then the kernel won't be able to mount it.