Red Hat Enterprise Linux 5 Administration Unleashed

Recovery and Repair 235Rescue ModeRescue mode allows the administrator to bypass the boot loader by instead booting off aninstallation media. Possible reasons to use rescue mode include. Corrupt boot loader that needs repair. Corrupt filesystem that can not be mounted and needs repairTo start rescue mode, boot from the first Red Hat Enterprise Linux installation CD. Afterbooting off the CD, the command used to enter rescue mode differs by architecture. Referto Table 10.5 for the command for your architecture.TABLE 10.5 Booting into Rescue Mode per ArchitectureArchitectureRescue Mode Commandx86, x86_64 Type linux rescue at GRUB promptIntel ItaniumType elilo linux rescue at EILO promptIBM POWERAppend rescue after kernel name at YABOOT prompt(IBM eServer iSeries,IBM eServer pSeries)IBM System zAdd rescue to the CMS conf parameter fileAfter booting into rescue mode, select the language and keyboard layout to use duringrescue 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 thatsends data to another system over the network has been added to the system. If you needto copy data to another system to save it before reinstalling or copying files to the systemto repair it, you will need to start the network.The next question is whether or not to try and mount the Linux filesystem. You canselect to skip this step, mount the filesystem, or mount the filesystem read-only. If youare not sure whether the filesystem can be mounted, you can select to mount it. If it can’tbe mounted, a message is displayed, and you are allowed to go back and select to skipmounting the filesystem. If the filesystem is successfully mounted, it is mounted underthe /mnt/sysimage/ directory. If you need to execute a command from the installedsystem, 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 exitrescue mode and reboot the system.Alternatively, you can boot from a disk created from the boot.iso image found in theimages/ directory of the first installation CD and then use the command from Table 10.5.After selecting the language and keyboard, select the location of the rescue image. Choosefrom the CD-ROM drive, hard drive, NFS, FTP, or HTTP. The location specified mustcontain the installation source files for the same version of Red Hat Enterprise Linux asthe boot.iso you used to create the boot media. Refer to Chapter 1, “Installing Red HatEnterprise Linux,” for details on setting up the installation source.10