Every user of any computer figures out sooner or later that files are occasionally lost. These losses have many causes: users may delete their own files accidentally, a bug can cause a program to corrupt its data file, a hardware failure may ruin an entire disk, and so on. The damage resulting from these losses can range from minor to expansive and can be very time-consuming to fix. To ensure against loss, one primary responsibility of a system administrator is planning and implementing a backup system that periodically copies all files on the system to some other location. It is also the administrator’s responsibility to see that backups are performed in a timely manner and that backup tapes (and other media) are stored safely and securely. This chapter will begin by discussing backup strategies and options and then turn to the tools that Unix systems provide for making them.
An excellent reference work about backups on Unix systems is Unix Backup and Recovery by W. Curtis Preston (O’Reilly & Associates). It covers the topics we are discussing here in complete detail and also covers material beyond the scope of this book (e.g., backing up and restoring databases).