The -B option is used when running BRU in the background. Normally, it is included as part of a shell script that is scheduled to run automatically. For example, the following line might be included in a script that is run by cron every night:
bru -c -B /usr
The -B option in the BRU command line tells BRU that it is running in the background and that it can expect no user intervention. It is specifically designed to prevent the situation in which a background backup process needs another tape, and because there is no one present to mount it, the process waits indefinitely for input. If -B is used, the process will terminate with an appropriate error code. NOTE: The -B option will be set automatically if BRU is started as a background process, that is, if the “&” shell option is included on the command line. For example:
bru -c /usr &
This is true when using the Bourne shell; it may not work for other shells.
If an operator is available, you may decide not to use the -B option in order to assure that the backup actually takes place. If -B is not specified, then BRU will indeed ask for help and the operator may be able to resolve the error condition for a successful run.
The -I option provides other options for communicating with BRU in the background. See Chapter 9, “Advanced Uses,” “Using BRU with brutalk: -I,” Appendix C, “The BRU Manual Page,” and Appendix H, “The brutalk Program.” The selection of -B or -I will depend on what the desired recovery is when interaction is necessary.