When things go wrong, there are ways to fix problems. However,
these methods require that you understand the system well. This
chapter describes how to boot into rescue mode, single-user mode,
and emergency mode, where you can use your own knowledge to repair
the system.
You might need to boot into one of these recovery modes for any
of the following reasons:
-
You are unable to boot normally into Red Hat Enterprise Linux
(runlevel 3 or 5).
-
You are having hardware or software problems, and you want to
get a few important files off of your system's hard drive.
-
You forgot the root password.
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 GRUB boot loader.
If the boot loader is overwritten in this manner, you cannot boot
Red Hat Enterprise Linux unless you can get into 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, boot in rescue mode and modify the
/boot/grub/grub.conf file.
For instructions on how to reinstall the GRUB boot loader from a
rescue environment, refer to Section
5.2.1 Reinstalling the Boot Loader.
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 one of the system
recovery modes, you might be able to resolve the problem or at
least get copies of your most important files.
What can you do if you forget your root password? To reset it to
a different password, boot into rescue mode or single-user mode,
and use the passwd command to reset the
root password.
