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DUMP(8) NetBSD System Manager's Manual DUMP(8)
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dump, rdump -- file system backup
dump [-0123456789aceFinStuX] [-B records] [-b blocksize] [-d density]
[-f file] [-h level] [-k read-blocksize] [-L label] [-l timeout]
[-r cachesize] [-s feet] [-T date] [-U dumpdev] [-x snap-backup]
dump [-W | -w]
(4.3BSD option syntax is implemented for backward compatibility, but not
dump examines files on a file system and determines which files need to
be backed up. These files are copied to the given disk, tape or other
storage 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
options below. By default, the same output file name is used for each
volume after prompting the operator to change media.
files-to-dump is either a single file system, or a list of files and
directories on a single file system to be backed up as a subset of the
file system. In the former case, files-to-dump may be the device of a
file system, the path to a currently mounted file system, the path to an
unmounted file system listed in /etc/fstab, or, if -F is given, a file
system image. 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 file system.
Any files with the superuser "log" flag (SF_LOG) set will be skipped.
These files are assumed to be wapbl(4) journal files and will not be
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 (but see
also the -i option below). The default level is 9.
-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).
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.
-c Modify the calculation of the default density and tape size to be
more appropriate for cartridge tapes.
Set tape density to density. The default is 1600 Bits Per Inch
-e Eject tape automatically if a tape change is required.
-F Indicates that files-to-dump is a file system image.
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
requires more volumes than the number of names given, the last
file name will be used for all remaining volumes after prompting
for media 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). Note that methods more secure
than rsh(1) (such as ssh(1)) can be used to invoke rmt(8) on the
remote host, via the environment variable RCMD_CMD. See rcmd(3)
for more details.
Honor the user "nodump" flag (UF_NODUMP) 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.
-i The dump is treated as level 9 but takes into account a previous
level 9, if one exists. This makes it possible to perform a
``true incremental'' dump.
The size in kilobytes of the read buffers, rounded up to a multi-
ple of the file system block size. Default is the value of the
The user-supplied text string label is placed into the dump
header, where tools like restore(8) and file(1) can access it.
Note that this label is limited to be at most LBLSIZE (currently
16) characters, which must include the terminating `\0'.
If a tape change is required, eject the tape and wait for the
drive to be ready again. This is to be used with tape changers
which automatically load the next tape when the tape is ejected.
If after the timeout (in seconds) the drive is not ready dump
falls back to the default behavior, and prompts the operator for
the next tape.
-n Whenever dump requires operator attention, notify all operators
in the group "operator" using wall(1).
Use that many buffers for read cache operations. A value of zero
disables the read cache altogether, higher values improve read
performance by reading larger data blocks from the disk and main-
taining them in an LRU cache. See the -k option for the size of
the buffers. Maximum is 512, the size of the cache is limited to
15% of the avail RAM by default.
-S 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, 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 for-
mat of date is the same as that of ctime(3). This option is use-
ful for automated dump scripts that wish to dump over a specific
period of time. The -T option and the -u option are mutually
-t All informational log messages printed by dump will have the time
prepended to them. Also, the completion time interval estima-
tions will have the estimated time at which the dump will com-
plete printed at the end of the line.
-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: file system name, increment level
and ctime(3) format dump date. There may be only one entry per
file system at each level. The file /etc/dumpdates may be edited
to change any of the fields, if necessary. If the -T option is
used or if a list of files or subdirectories is being dumped (as
opposed to an entire file system), then -u is ignored.
Same as -u but specifies the device in /etc/dumpdates as dumpdev.
This option can be used with subdir dumps and with the -T option.
-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 option 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 option is set, all other options are ignored, and dump
-w Like -W, but prints only those file systems which need to be
-X Similar to -x but uses a file system internal snapshot on the
file system to be dumped.
Use a snapshot with snap-backup as backup for this dump. See
fss(4) for more details.
If dump honors the "nodump" flag (UF_NODUMP), files with the "nodump"
flag will not be backed up. If a directory has the "nodump" flag, this
directory and any file or directory under it will not be backed up.
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 option, 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 completed, cur-
rent transfer rate, and estimated finished time, will be written to the
standard error output.
The historic alternate name rdump was once required when dumping to a
remote host. This functionality is now built into dump itself.
If the following environment variables exist, they are used by dump.
TAPE If no -f option was specified, dump will use the device spec-
ified via TAPE as the dump device. TAPE may be of the form
"tapename", "host:tapename", or "user@host:tapename".
RCMD_CMD dump will use RCMD_CMD rather than rsh(1) to invoke rmt(8) on
the remote machine.
TIMEFORMAT can be used to control the format of the timestamps produced
by the -t option. TIMEFORMAT is a string containing embedded
formatting commands for strftime(3). The total formatted
string is limited to about 80 characters, if this limit is
exceeded then "ERROR: TIMEFORMAT too long, reverting to
default" will be printed and the time format will revert to
the default one. If TIMEFORMAT is not set then the format
string defaults to "%T %Z"
/dev/nrst0 default tape unit to use. Taken from _PATH_DEFTAPE in
/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
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.
chflags(1), rcmd(1), stty(1), wall(1), fts(3), rcmd(3), fss(4), st(4),
fstab(5), environ(7), restore(8), rmt(8)
A dump command appeared in Version 4 AT&T UNIX.
The -i flag was inspired by the -x flag from Sun's Solstice Backup util-
At least the following caveats can be mentioned.
· Fewer than 32 read errors on the file system 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 options does not report file systems 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
required to scan the directory (as this is done via the fts(3) rou-
tines rather than directly accessing the file system).
· 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 provided more assistance for the operator running restore(8).
· Snapshot support is experimental. Be sure you have a backup before
you use it.
NetBSD 9.0 March 25, 2019 NetBSD 9.0