Many UNIX system problems are caused by files that have changed (or are missing). BRU’s differences mode can often help you in trouble-shooting these types of problems-if you do a little advance preparation. First, use BRU to create a “reference” backup of your entire system (or just the basic UNIX system programs in the root filesystem). This should be done when your system is properly configured and working properly. Save this reference archive for the future (make sure that the tape is write-protected and properly marked with a label).
If you experience system problems later on, you can use the reference archive with the -d mode to detect any changes in your system. Quite often, this will help you in tracking down difficult problems. The reference archive tape might also be useful in case you need to recover from a system crash.