Installation guide

Chapter 3.

Rescue Mode

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 and

single user mode, where you can use your own knowledge to repair the system.

3.1. What is Rescue Mode?

Rescue mode provides the ability to boot a small Linux environment entirely from a diskette,

CD-ROM, or using some other method.

As the name implies, rescue mode is provided to rescue you from something. During normal

operation, your Red Hat Linux system uses ﬁles located on your system’s hard drive to do

everything — run programs, store your ﬁles, and more.

However, there may be times when you are unable to get Linux running completely enough

to access its ﬁles on your system’s hard drive. Using rescue mode, you can access the ﬁles

stored on your system’s hard drive, even if you cannot actually run Linux from that hard

drive.

Normally, you will need to get into rescue mode for one of two reasons:

• You are unable to boot Linux.

• You are having hardware or software problems, and you want to get a few important ﬁles

off your system’s hard drive.

Next, we take a closer look at each of these scenarios.

3.1.1. Unable to Boot Linux

This problem is often caused by the installation of another operating system after you have

installed Red Hat Linux. Some other operating systems assume that you have no other op-

erating systems on your computer, and they overwrite the Master Boot Record (MBR) that

originally contained the GRUB or LILO boot loader. If the boot loader is overwritten in this

manner, you will not be able to boot Red Hat Linux unless you can get into rescue mode.

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 will not be

able to ﬁnd it to mount the partition. To ﬁx this problem, boot in rescue mode and modify

/boot/grub/grub.conf if you are using GRUB or /etc/lilo.conf if you are using LILO.

3.1.2. Hardware/Software Problems

This category includes a wide variety of different situations. Two examples include failing

hard drives and forgetting to run LILO after building a new kernel (if you are using LILO as

your boot loader). If you are using GRUB, you do not have to execute a command to reread

the GRUB conﬁguration ﬁle. However, if you specify an invalid root device or kernel in the

GRUB conﬁguration ﬁle, you might not know until you reboot your computer.