-0-9 Dump levels. A level 0, full backup, guarantees the entire file
system is copied (but see also the -h option below). A level
number above 0, incremental backup, tells dump to copy all files
new or modified since the last dump of any lower level. The
default level is 0. -a "auto-size". Bypass all tape length considerations, and enforce
writing until an end-of-media indication is returned. This fits
best for most modern tape drives. Use of this option is
particularly recommended when appending to an existing tape, or
using a tape drive with hardware compression (where you can never
be sure about the compression ratio). -n Whenever dump requires operator attention, notify all operators
in the group "operator" by means similar to a wall(1). -u Update the dumpdates file after a successful dump. The format of
the dumpdates file is readable by people, consisting of one free
format record per line: file system name, increment level and
ctime(3) format dump date. There may be only one entry per file
system at each level. The dumpdates file may be edited to change
any of the fields, if necessary. The default path for the
dumpdates file is /etc/dumpdates, but the -D option may be used
to change it.