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Rescuing Linux Systems--Generic and Distribution-Specific Safety Nets
Sending Out an SOS
July 8, 2002
The time comes when every Linux system administrator experiences a system failure. Hardware failures are usually resolved quickly enough by replacing a deceased motherboard, power supply, or controller, but component failure can have other side effects, especially in disk subsystems where errant or incomplete writes may corrupt boot information and filesystems. The true twilight zone for system administrators occurs when an otherwise useful system is unbootable due to disk corruption or accidental system misconfiguration--your data is just a few inches away, but is inaccessible for one reason or another.
The easiest solution to this sort of problem is a bootable disk known as a "rescue disk," located on removable media such as a floppy disk or CD. These are designed to help you boot failed systems, resolve or work around common problems, and quickly restore your system to self-sufficiency.
Linux rescue disks generally fall into two distinct classes, each with its own advantages and disadvantages. The first class of these are rescue disks that are provided with or produced by a specific Linux distribution and are therefore targeted toward correcting problems encountered on a machine running that distribution. These distribution-specific rescue disks may either be floppies created during the installation process, or may be boot options that are available from the distribution's installation CD. In either case, such distribution-specific rescue disks reflect the boot loader, filesystems, and tools used by that distribution.
The second class of rescue disks are distribution-independent, single-floppy or single-CD rescue disks that are designed to help you recover any Linux system, regardless of the distribution on which it is based. The fact that these types of rescue disks are independent of any given distribution makes them a flexible solution that you can use to repair and recover many different kinds of Linux systems. At the same time, distribution-independent rescue disks may not be able to help you if the machine you are trying to repair uses filesystems or depends on custom software that is not supported outside of a specific distribution.
Both of these types of rescue disks are like insurance policies--you hope that you don't have to use them, but you'll be glad that you have them if you need them. This article discusses the kinds of problems that typically require the use of a rescue disk, highlights the rescue mechanisms provided with various Linux distributions, and concludes by comparing and contrasting some of the more popular and powerful distribution-independent rescue disks that are freely available on the Web today.