Linux Rescue Mode

Reinstall Corrupted Bootloader

Overview

• The Linux rescue mode is a special boot mode for fixing critical issues, such as reinstalling a corrupted stage 1bootloader or accessing a problematic /boot file system, that have rendered the system unbootable. In this training session, you will:
• Boot the system into the rescue mode using the RHEL installation DVD with networking disabled and file systems mounted in read-write mode in the chroot environment
• Reinstall Corrupted Bootloader using grub-install
• Reinstall Corrupted Bootloader from the grub Shell
• Install Lost/Corrupted System Files

Boot RHEL into the Rescue Mode

• 1. Boot the system with the installation DVD
• 2. Choose Rescue Installed System from the boot menu and press Enter.
• 3. Select a language and keyboard on subsequent screens.
• 4. Choose Local CD/DVD and press OK.
• 5. Choose no when asked whether you want network interfaces to start in the rescue mode.
• 6. Choose Continue and press Enter.
• 7. Continue searches for a RHEL installation and, if found, mounts the / file system on /mnt/sysimage in read/write mode.
• 8. Press OK again to go to the command prompt.
• 9. Run the chroot command to make all file systems appear as if they are mounted directly under.

–# chroot /mnt/sysimage

 

Reinstall Corrupted Bootloader using grub-install

• 1. Boot the system into rescue mode with all file systems mounted read/write in the chroot environment.
• 2. Issue the grub-install command to reinstall the bootloader on the boot disk’s MBR:

# grub-install –root-directory=/ /dev/sda

• 3. Issue exit twice to go back, then select Reboot to restart the system.

Reinstall Corrupted Bootloader from the grub Shell

• 1. Boot the system into rescue mode with all file systems mounted read/write in the chroot environment.
• 2. Issue the grub command to invoke the grub shell:

# grub

• 3. Run the root command to set the current root device:

–grub> root (hd0,0)

• 4. Execute the setup command to install the bootloader on the /dev/sda disk:

–grub> setup (hd0)

• 5. Issue quit to exit out of the grub shell, and then exit twice to go back.

6. Select Reboot to restart the system

 

Install a Lost or Corrupted System File

• 1. Boot the system into rescue mode with all file systems mounted read/write in the non-chroot environment.
• 2. Copy the lost/corrupted file (in this case /bin/mount) to the /mnt/sysimage/bin directory:

# cp /bin/mount /mnt/sysimage/bin

• 3. Confirm the file copy:

# ls -l /mnt/sysimage/bin

• 4. Issue the exit command twice to go back.
• 6. Select Reboot to restart the system.