How to Boot a System into Rescue Mode from Installation DVD/ISO on OEL/CentOS 7

Booting a system into rescue mode from an installation DVD or ISO on CentOS 7 is a useful way to recover or repair a Linux system.

Steps:

1.(Attach an ISO image): Insert bootable media such as USB or DVD or ISO image, I would like to use ISO image because it can be easily mounted on the system without going to the data center.

reboot

2. Boot up the CentOS 7 system from the ISO image and wait for the boot menu to appear. Select the ‘Troubleshooting’ option and press enter.

3. In the next screen, select the ‘Rescue a CentOS Linux system’ option and press enter.

4. At the next screen, input '1' and then press enter to continue. The rescue environment will now attempt to find your Linux installation and mount it under the directory '/mnt/sysimage', but in read-only mode.

5.Now, your system has been mounted under ‘/mnt/sysimage’. Even if your file system is mounted, the default root partition while in Anaconda rescue mode is a temporary root partition, not the root partition of the file system used in normal user mode such as multi-user.target or graphical.target.

6. Run the following command to make the system to use root partition of your file system instead of Anaconda rescue mode environment root partition. It basically, switch to the ‘chroot’ environment:

chroot /mnt/sysimage

This method can help to repair the corrupted root file system and various other issues.Once you have finished troubleshooting, type ‘exit’ twice to boot the system back to normal mode