To analyze or repair a system failure, you might need to boot into the system. But, what if the boot loader is corrupt or what if the filesystem can’t be mounted anymore? Red Hat Enterprise Linux includes alternative boot methods for system repair: rescue mode, single user mode, and emergency mode.
After booted into one of these modes, a set of commonly used editors such as Emacs and Vi are available along with commonly used utilities such as e2fsck for repairing a filesystem and grub-install for repairing the boot loader on an x86 or x86_64 system. IBM System z Add rescue to the CMS conf parameter file. After booting into rescue mode, select the language and keyboard layout to use during rescue mode. Next, decide whether to start the network. If the system has been compromised, you probably don’t want to start a network connection in case a program that sends data to another system over the network has been added to the system. If you need to copy data to another system to save it before reinstalling or copying files to the system to repair it, you will need to start the network.
The next question is whether or not to try and mount the Linux filesystem. You can select to skip this step, mount the filesystem, or mount the filesystem read-only. If you are not sure whether the filesystem can be mounted, you can select to mount it. If it can’t be mounted, a message is displayed, and you are allowed to go back and select to skip mounting the filesystem. If the filesystem is successfully mounted, it is mounted under the /mnt/sysimage/ directory. If you need to execute a command from the installed system, remember the path to the command should be prepended with /mnt/sysimage/.
A shell prompt is displayed next. Use this shell to repair your system. Type exit to exit rescue mode and reboot the system.
Alternatively, you can boot from a disk created from the boot.iso image found in the images/ directory of the first installation CD and then use the command from.
After selecting the language and keyboard, select the location of the rescue image. Choose from the CD-ROM drive, hard drive, NFS, FTP, or HTTP. The location specified must contain the installation source files for the same version of Red Hat Enterprise Linux as the boot.iso you used to create the boot media.
TIP: If using NFS, FTP or HTTP remember to allow the system being booted into rescue mode access to the directory containing the installation files.
If you select NFS, FTP, or HTTP, a network connection will be established, if possible, before continuing. If the location does not require a network connection, rescue mode optionally allows the administrator to start a network connection. After choosing whether to start the network, select whether to mount the filesystem. As with using rescue mode from the installation CD or DVD, use the shell to repair the system, and type exit to reboot the system when finished.