+.SS Command-line options
+Most of the behaviour of
+.B rsync-backup
+is controlled by a configuration file, described starting with the
+section named
+.B Configuration commands
+below.
+But a few features are controlled by command-line options.
+.TP
+.B \-h
+Show a brief help message for the program, and exit successfully.
+.TP
+.B \-V
+Show
+.BR rsync-backup 's
+version number and some choice pieces of build-time configuration, and
+exit successfully.
+.TP
+.BI "\-c " conf
+Read
+.I conf
+instead of the default configuration file (shown as
+.B conf
+in the
+.B \-V
+output).
+.TP
+.B \-v
+Produce verbose progress information on standard output while the backup
+is running. This keeps one amused while running a backup
+interactively. In any event,
+.B rsync-backup
+will report failures to standard error, and otherwise run silently, so
+it doesn't annoy unnecessarily if run by
+.BR cron (8).
+.SS Backup process
+Backing up a filesystem works as follows.
+.hP \*o
+Make a snapshot of the filesystem on the client, and ensure that the
+snapshot is mounted. There are some `trivial' snapshot types which use
+the existing mounted filesystem, and either prevent processes writing to
+it during the backup, or just hope for the best. Other snapshot types
+require the snapshot to be mounted somewhere distinct from the main
+filesystem, so that the latter can continue being used.
+.hP \*o
+Run
+.B rsync
+to copy the snapshot to the backup volume \(en specifically, to
+.IB host / fs / new \fR.
+If this directory already exists, then it's presumed to be debris from a
+previous attempt to dump this filesystem:
+.B rsync
+will update it appropriately, by adding, deleting or modifying the
+files. This means that retrying a failed dump \(en after fixing whatever
+caused it to go wrong, obviously! \(en is usually fairly quick.
+.hP \*o
+Run
+.B fshash
+on the client to generate a `digest' describing the contents of the
+filesystem, and send this to the server as
+.IB host / fs / new .fshash \fR.
+.hP \*o
+Release the snapshot: we don't need it any more.
+.hP \*o
+Run
+.B fshash
+over the new backup; specifically, to
+.BI tmp/fshash. host . fs . date \fR.
+This gives us a digest for what the backup volume actually stored.
+.hP \*o
+Compare the two
+.B fshash
+digests. If they differ then dump the differences to the log file and
+report a backup failure. (Backups aren't any good if they don't
+actually back up the right thing. And you stand a better chance of
+fixing them if you know that they're going wrong.)
+.hP \*o
+Commit the backup, by renaming the dump directory to
+.IB host / fs / date
+and the
+.B fshash
+digest file to
+.IB host / fs / date .fshash \fR.