When things go wrong, there are ways to fix problems. However, these methods require that you understand the system well. This chapter contains information on common problems you might face and it also describes installation program rescue mode, which can be used to fix these problems.
You might need to boot into installation program rescue mode for any of the following reasons:
You are unable to boot into Red Hat Enterprise Linux normally.
You are having hardware or software problems, and you want to recover data from your system's hard drive.
You forgot the root password.
31.1.1. Unable to Boot into Red Hat Enterprise Linux
This problem is often caused by the installation of another operating system after you have installed Red Hat Enterprise Linux. Some other operating systems assume that you have no other operating system(s) on your computer. They overwrite the Master Boot Record (MBR) that originally contained the GRUB2 boot loader. If the boot loader is overwritten in this manner, you cannot boot Red Hat Enterprise Linux unless you can boot into installation program rescue mode and reconfigure the boot loader.
Another common problem occurs when using a partitioning tool to resize a partition or create a new partition from free space after installation, and it changes the order of your partitions. If the partition number of your
partition changes, the boot loader might not be able to find it to mount the partition. To fix this problem, you will need to reinstall the boot loader. See Section 31.2.2, “Reinstalling the Boot Loader”
for instructions on how to do this.
31.1.2. Hardware and Software Problems
This category includes a wide variety of different situations. Two examples include failing hard drives and specifying an invalid root device or kernel in the boot loader configuration file. If either of these occur, you might not be able to reboot into Red Hat Enterprise Linux. However, if you boot into installation program rescue mode, you might be able to resolve the problem or at least get copies of your most important files.
31.1.3. Resetting the Root Password