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DUMP(8) OpenBSD System Manager's Manual DUMP(8)
dump - filesystem backup
dump [-0123456789acnu] [-B records] [-b blocksize] [-d density] [-f file]
[-h level] [-s feet] [-T date] files-to-dump
dump [-W | -w]
(The 4.3BSD option syntax is implemented for backward compatibility, but
is not documented here.)
dump examines files on a filesystem and determines which files need to be
backed up. These files are copied to the given disk, tape or other stor-
age medium for safe keeping (see the -f option below for doing remote
backups). A dump that is larger than the output medium is broken into
multiple volumes. On most media the size is determined by writing until
an end-of-media indication is returned. This can be enforced by using
the a option.
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 block count op-
tions below. By default, the same output file name is used for each vol-
ume after prompting the operator to change media.
files-to-dump is either a mountpoint of a filesystem, or a list of files
and directories on a single filesystem to be backed up as a subset of the
filesystem. In the former case, either the path to a mounted filesystem,
or the device of an unmounted filesystem can be used. In the latter
case, certain restrictions are placed on the backup: -u is ignored, the
only dump level that is supported is -0, and all of the files must reside
on the same filesystem.
The following options are supported by dump:
-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 a lower level. The de-
fault level is 0.
-a ``auto-size''. Bypass all tape length considerations, and enforce
writing until an end-of-media indication is returned. This op-
tion is recommended for most modern tape drives. Use of this op-
tion 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 volume, rounded down to a multiple of
the blocksize. This option overrides the calculation of tape
size based on length and density.
The number of kilobytes per dump record. Since the IO system
slices all requests into chunks of MAXBSIZE (typically 64KB), it
is not possible to use a larger blocksize without having problems
later with restore(8). Therefore dump will constrain writes to
-c Change the defaults for use with a cartridge tape drive, with a
density of 8000 bpi, and a length of 1700 feet.
Set tape density to density. The default is 1600BPI.
Write the backup to file; file may be a special device file like
/dev/rst0 (a tape drive), /dev/rsd1c (a disk drive), an ordinary
file, or `-' (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 re-
quires more volumes than the number of names given, the last file
name will used for all remaining volumes after prompting for me-
dia changes. If the name of the file is of the form
``host:file'', or ``user@host:file'', dump writes to the named
file on the remote host using rmt(8).
Honor the user ``nodump'' flag only for dumps at or above the
given level. The default honor level is 1, so that incremental
backups omit such files but full backups retain them.
-n Whenever dump requires operator attention, notify all operators
in the group ``operator'' by means similar to a wall(1).
Attempt to calculate the amount of tape needed at a particular
density. If this amount is exceeded, dump 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 /etc/dumpdates. The format
of date is the same as that of ctime(3). This option is useful
for automated dump scripts that wish to dump over a specific pe-
riod of time. The -T flag is mutually exclusive from the -u
-u Update the file /etc/dumpdates after a successful dump. The for-
mat of /etc/dumpdates is readable by people, consisting of one
free format record per line: filesystem name, increment level and
ctime(3) format dump date. There may be only one entry per
filesystem at each level. The file /etc/dumpdates may be edited
to change any of the fields, if necessary. If a list of files or
subdirectories is being dumped (as opposed to and entire filesys-
tem), then -u is ignored.
-W dump tells the operator what file systems need to be dumped.
This information is gleaned from the files /etc/dumpdates and
/etc/fstab. The -W flag causes dump to print out, for each file
system in /etc/dumpdates the most recent dump date and level, and
highlights those file systems that should be dumped. If the -W
flag is set, all other options are ignored, and dump exits imme-
-w Is like W, but prints only those filesystems which need to be
dump 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 -n flag, dump interacts with the operator on dump's con-
trol terminal at times when dump can no longer proceed, or if something
is grossly wrong. All questions dump poses must be answered by typing
``yes'' or ``no'', appropriately.
Since making a dump involves a lot of time and effort for full dumps,
dump checkpoints itself at the start of each tape volume. If writing
that volume fails for some reason, dump will, with operator permission,
restart itself from the checkpoint after the old tape has been rewound
and removed, and a new tape has been mounted.
dump tells the operator what is going on at periodic intervals, 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
controlling dump is busy, 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/nrst1 /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
- After a level 0, dumps of active file systems 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 num-
ber 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.
If dump receives a SIGINFO signal (see the ``status'' argument of
stty(1)) whilst a backup is in progress, statistics on the amount com-
pleted, current transfer rate, and estimated finished time, will be writ-
ten to the standard error output.
/dev/rst0 default tape unit to dump to
/dev/rst* Raw SCSI tape interface
/etc/dumpdates dump date records
/etc/fstab dump table: file systems and frequency
/etc/group to find group operator
stty(1), fts(3), fstab(5), rcmd(3), restore(8), rmt(8)
Many, and verbose.
dump exits with zero status on success. Startup errors are indicated
with an exit code of 1; abnormal termination is indicated with an exit
code of 3.
Fewer than 32 read errors on the filesystem are ignored.
Each reel requires a new process, so parent processes for reels already
written just hang around until the entire tape is written.
dump with the -W or -w flags does not report filesystems that have never
been recorded in /etc/dumpdates, even if listed in /etc/fstab.
When dumping a list of files or subdirectories, access privileges are re-
quired to scan the directory (as this is done via the fts(3) routines
rather than directly accessing the filesystem).
It would be nice if dump knew about the dump sequence, kept track of the
tapes scribbled on, told the operator which tape to mount when, and pro-
vided more assistance for the operator running restore.
A dump command appeared in Version 6 AT&T UNIX.
4th Berkeley Distribution June 4, 1997 4
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.
(Corrections, notes, and links courtesy of RocketAware.com)
FreeBSD Sources for dump(8)
OpenBSD sources for dump(8)
Up to: File System Operations - Operations for entire file-systems (quotas, configuration, consistency, mount, unmount, et al)
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