Running Linux, Third Edition

What to Do in an Emergency

It’s not difficult to make a simple mistake as root that can cause real problems on your system, such as not being able to log in or losing important files. This is especially true for novice system administrators who are beginning to explore the system. Nearly all new system admins learn their lessons the hard way, by being forced to recover from a real emergency. In this section, we’ll give you some hints about what to do when the inevitable happens.

You should always be aware of preventative measures that reduce the impact of such emergencies. For example, take backups of all important system files, if not the entire system. If you happen to have a Linux distribution on CD-ROM, the CD-ROM itself acts as a wonderful backup for most files (as long as you have a way to access the CD-ROM in a tight situation—more on this later). Backups are vital to recovering from many problems; don’t let the many weeks of hard work configuring your Linux system go to waste.

Also, be sure to keep notes on your system configuration, such as your partition table entries, partition sizes and types, and filesystems. If you were to trash your partition table somehow, fixing the problem might be a simple matter of rerunning fdisk, but this only helps as long as you can remember what your partition table used to look like. (True story: one of the authors once did this by booting a blank floppy, and had no record of the partition table contents. Needless to say, some guesswork ...