Rescue Mode

Rescue mode is an environment you can use to fix a system that does not boot normally. To bring a system up in rescue mode, boot the system from the first installation CD, the Net Boot CD, or the install DVD. From the install DVD, select Rescue installed system from the Welcome menu (page 56). From the first installation CD and the Net Boot CD, enter the rescue (FEDORA) or boot rescue (RHEL) boot parameter. The boot process may take several minutes. The system then comes up in rescue mode.

In rescue mode, you can change or replace configuration files, check and repair partitions using fsck, rewrite boot information, and more. The rescue screen first asks if you want to set up the network interface. This interface is required if you want to copy files from other systems on the LAN or download files from the Internet. When you choose to set up the network interface, you need to decide whether to have DHCP automatically configure the network connection or to manually supply the IP address and netmask of the interface, as well as the IP addresses of the gateway and DNS server(s).

If the rescue setup finds an existing Linux installation, you can choose to mount it under /mnt/sysimage, optionally in readonly mode. With the existing installation mounted, once the system displays a shell prompt (similar to sh-3.2#), you can give the command chroot /mnt/sysimage to access the existing installation as it would be if you booted normally, with the existing installation’s root directory available as / (root). If you choose not to mount the existing installation, you are running a rescue system with standard tools mounted in standard locations (/bin, /usr/bin, and so on). Partitions from your local installation are available for fixing or mounting. When you exit from the rescue shell, the system reboots. Remove the CD or DVD if you want to boot from the hard drive.

Source of Information : Prentice Hall A Practical Guide to Fedora and Red Hat Enterprise Linux 5th Edition