How can Red Hat Enterprise Linux system be accessed when booting into rescue mode or runlevel 1 is not possible?

If booting into runlevel 1 or into the rescue environment using the installation CD is not possible, there is still hope in fixing the operating system. The system might still be able to boot into "emergency" mode. This "runlevel" is even more basic than runlevel 1. It does not execute the /etc/rc.d/rc.sysinit script and it mounts the root filesystem in read-only mode.

To go into "emergency" mode, boot the system until the grub bootloader appears. Before the countdown timer expires, hit 'e'. Select the kernel line using the arrow keys then hit 'e' again. This will position the cursor to the end of the kernel line. Hit the spacebar then type "emergency". Hit 'Enter' then 'b' to boot.

The system should boot quickly and prompt for the root password then it will mount the root partition in read-only mode and opens a minimal shell. Mount the /proc partition:

mount /proc

Then, remount the root partition in read-write mode to allow editing of configuration files:

mount -o remount,rw /

Begin troubleshooting.