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System Recovery in LINUX

Basic System Recovery in Linux

When things go wrong, there are ways to _x 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.

Common Problems

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

You are having hardware or software problems, and you want to get a few important _les off of your system's hard drive.

You forgot the root password.

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 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 recon_gure 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 _nd it to mount the partition.

To _x this problem, boot in rescue mode and modify the /boot/grub/grub.conf _le.

Hardware/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 con_guration _le. 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 _les.

Root Password

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.

Booting into Rescue Mode

Rescue mode provides the ability to boot a small Red Hat Enterprise Linux environment entirely from CD-ROM, or some other boot method, instead of the system's hard drive.

As the name implies, rescue mode is provided to rescue you from something. During normal operation, your Red Hat Enterprise Linux system uses _les located on your system's hard drive to do everything . run programs, store your _les, and more.

However, there may be times when you are unable to get Red Hat Enterprise Linux running completely enough to access _les on your system's hard drive. Using rescue mode, you can access the _les stored on your system's hard drive, even if you cannot actually run Red Hat Enterprise Linux from that hard drive.