Linux Rescue mode provides us the ability to boot to a limited Linux environment by using a CD-ROM, DVD, or some other boot method instead of the system's hard drive.
Normally, Red Hat Linux Operating System uses files kept on hard drive to run your machine.
If there is some problem, which prevent you from getting inside the Red Hat Linux to access files on system's hard drive, using Linux rescue mode or Linux rescue environment, you can access the files stored on your system's hard drive.
To boot to Linux resue mode or Linux rescue environment, you should have the RedHat Linux installation media (CD or DVD). Configure your machine's BIOS to boot from the installation media.
Once you have booted using the installation media (either the first CD/ROM of the five CD/ROM installation set, or RedHat installation DVD/ROM) enter the following command at the installation boot prompt
Once booted in Linux rescue mode, you will be prompted to answer some questions like installation language, keyboard type, TCP/IP configuration (IP address, subnet mask, gate way address, DNS server address). You will get a message stating
“The rescue environment will now attempt to find your Linux installation and mount it under the directory /mnt/sysimage. You can then make any changes required to your system. If you want to proceed with this step choose 'Continue'. You can also choose to mount your file systems read-only instead of read-write by choosing 'Read-only'. If for some reason this process fails you can choose 'Skip' and this step will be skipped and you will go directly to a command shell.”
Select “Continue” to proceed. Now you will get a message stating that your system has been mounted under /mnt/sysimage.
Click “OK” to continue to Linux Rescue mode.
The default root partition while in Linux rescue mode is a temporary root partition, not the root partition of the file system used during normal boot. You can change the root partition of the rescue mode environment to the root partition of your file system by executing the "chroot" command as shown below.
sh-3.1# chroot /mnt/sysimage
Note: Remember, your existing Linux system has been mounted under /mnt/sysimage folder.