option syntax is implemented for backward compatibility, but
is not documented here.)
utility examines files
on a file system
and determines which files
need to be backed up.
are copied to the given disk, tape or other
storage medium for safe keeping (see the
option below for doing remote backups).
A dump that is larger than the output medium is broken into
On most media the size is determined by writing until an
end-of-media indication is returned.
This can be enforced
by using the
On media that cannot reliably return an end-of-media indication
(such as some cartridge tape drives)
each volume is of a fixed size;
the actual size is determined by the tape size and density and/or
By default, the same output file name is used for each volume
after prompting the operator to change media.
The file system to be dumped is specified by the argument
as either its device-special file or its mount point
(if that is in a standard entry in
The following options are supported by
A level 0, full backup,
guarantees the entire file system is copied
(but see also the
A level number above 0,
tells dump to
copy all files new or modified since the
last dump of any lower level.
The default level is 0.
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).
The number of kilobytes per output volume, except that if it is
not an integer multiple of the output block size,
the command uses the next smaller such multiple.
This option overrides the calculation of tape size
based on length and density.
The number of kilobytes per output block.
The default block size is 10.
Specify the cache size in megabytes.
This will greatly improve performance
at the cost of
possibly not noticing changes in the file system between passes.
recommended that you always use this option when dumping a snapshot.
forks, and the actual memory use may be larger than the specified cache
The recommended cache size is between 8 and 32 (megabytes).
Change the defaults for use with a cartridge tape drive, with a density
of 8000 bpi, and a length of 1700 feet.
Specify an alternate path to the
The default is
Set tape density to
The default is 1600BPI.
Write the backup to
may be a special device file
(a tape drive),
(a floppy disk drive),
an ordinary file,
(the standard output).
Multiple file names may be given as a single argument separated by commas.
Each file will be used for one dump volume in the order listed;
if the dump requires more volumes than the number of names given,
the last file name will used for all remaining volumes after prompting
for media changes.
If the name of the file is of the form
writes to the named file on the remote host using
The default path name of the remote
this can be overridden by the environment variable
to execute the
script string defined by
for the output device of each volume.
This child pipeline's
is redirected from the
output stream, and the environment variable
is set to the current volume number being written.
After every volume, the writer side of the pipe is closed and
is executed again.
Subject to the media size specified by
each volume is written in this manner as if the output were a tape drive.
Honor the user
only for dumps at or above the given
The default honor level is 1,
so that incremental backups omit such files
but full backups retain them.
This option is to notify
that it is dumping a live file system.
To obtain a consistent dump image,
takes a snapshot of the file system in the
directory in the root of the file system being dumped and
then does a dump of the snapshot.
The snapshot is unlinked as soon as the dump starts, and
is thus removed when the dump is complete.
This option is ignored for unmounted or read-only file systems.
directory does not exist in the root of the file system being dumped,
a warning will be issued and the
will revert to the standard behavior.
This problem can be corrected by creating a
directory in the root of the file system to be dumped;
its owner should be
its group should be
and its mode should be
requires operator attention,
notify all operators in the group
by means similar to a
Display an estimate of the backup size and the number of
tapes required, and exit without actually performing the dump.
Attempt to calculate the amount of tape needed
at a particular density.
If this amount is exceeded,
prompts for a new tape.
It is recommended to be a bit conservative on this option.
The default tape length is 2300 feet.
Use the specified date as the starting time for the dump
instead of the time determined from looking in
The format of date is the same as that of
This option is useful for automated dump scripts that wish to
dump over a specific period of time.
option is mutually exclusive from the
after a successful dump.
The format of
is readable by people, consisting of one
free format record per line:
file system name,
format dump date.
There may be only one entry per file system at each level.
may be edited to change any of the fields,
The default path for the
option may be used to change it.
Tell the operator what file systems need to be dumped.
This information is gleaned from the files
to print out, for each file system in
the most recent dump date and level,
and highlights those file systems that should be dumped.
option is set, all other options are ignored, and
but prints only those file systems which need to be dumped.
Directories and regular files which have their
set will be omitted along with everything under such directories,
subject to the
utility requires operator intervention on these conditions:
end of tape,
end of dump,
tape write error,
tape open error or
disk read error (if there are more than a threshold of 32).
In addition to alerting all operators implied by the
interacts with the operator on
control terminal at times when
can no longer proceed,
or if something is grossly wrong.
be answered by typing
Since making a dump involves a lot of time and effort for full dumps,
checkpoints itself at the start of each tape volume.
If writing that volume fails for some reason,
with operator permission,
restart itself from the checkpoint
after the old tape has been rewound and removed,
and a new tape has been mounted.
utility tells the operator what is going on at periodic intervals
(every 5 minutes, or promptly after receiving
including usually low estimates of the number of blocks to write,
the number of tapes it will take, the time to completion, and
the time to the tape change.
The output is verbose,
so that others know that the terminal
and will be for some time.
In the event of a catastrophic disk event, the time required
to restore all the necessary backup tapes or files to disk
can be kept to a minimum by staggering the incremental dumps.
An efficient method of staggering incremental dumps
to minimize the number of tapes follows:
Always start with a level 0 backup, for example:
/sbin/dump -0u -f /dev/nsa0 /usr/src
This should be done at set intervals, say once a month or once every two months,
and on a set of fresh tapes that is saved forever.
After a level 0, dumps of active file systems (file systems with files
that change, depending on your partition layout some file systems may
contain only data that does not change) are taken on a daily basis,
using a modified Tower of Hanoi algorithm,
with this sequence of dump levels:
3 2 5 4 7 6 9 8 9 9 ...
For the daily dumps, it should be possible to use a fixed number of tapes
for each day, used on a weekly basis.
Each week, a level 1 dump is taken, and
the daily Hanoi sequence repeats beginning with 3.
For weekly dumps, another fixed set of tapes per dumped file system is
used, also on a cyclical basis.
After several months or so, the daily and weekly tapes should get
rotated out of the dump cycle and fresh tapes brought in.
or device to dump to if the
option is not used.
Fewer than 32 read errors on the file system are ignored, though all
errors will generate a warning message.
This is a bit of a compromise.
In practice, it is possible to generate read errors when doing dumps
on mounted partitions if the file system is being modified while the
Since dumps are often done in an unattended fashion using
jobs asking for Operator intervention would result in the
However, there is nothing wrong with a dump tape written when this sort
of read error occurs, and there is no reason to terminate the
Each reel requires a new process, so parent processes for
reels already written just hang around until the entire tape
utility with the
options does not report file systems that have never been recorded
even if listed in
It would be nice if
knew about the dump sequence,
kept track of the tapes scribbled on,
told the operator which tape to mount when,
and provided more assistance
for the operator running
utility cannot do remote backups without being run as root, due to its
This will be fixed in a later version of
Presently, it works if you set it setuid (like it used to be), but this
might constitute a security risk.