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 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, 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 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.
Rewinding or ejecting tape features after a close operation
on a tape device
depend on the name of the tape unit device used. See
the -f option
and st(4) for more information.
The options are as follows:
-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 default
level is 0.
-a ``auto-size''. Bypass all tape length considerations, and enforce
writing until an end-of-media indication is
returned. This
option is recommended 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).
-B records
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.
-b blocksize
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
MAXBSIZE.
-c Change the defaults for use with a cartridge tape
drive, with a
density of 8000 bpi, and a length of 1700 feet.
-d density
Set tape density to density. The default is
1600BPI.
-f file
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).
-h level
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).
-s feet
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.
-T date
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
period of time. The -T flag is mutually exclusive
from the -u
flag.
-u Update the file /etc/dumpdates after a successful
dump. The format
of /etc/dumpdates is human readable, 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 an entire filesystem),
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 immediately.
-w Same as -W, but prints only those filesystems which
need to be
dumped.
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
is 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 control
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:
+o 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
forever.
+o 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 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.
If dump receives a SIGINFO signal (see the ``status'' argument of
stty(1)) whilst a backup is in progress, statistics on the
amount completed,
current transfer rate, and estimated finished time,
will be written
to the standard error output.
TAPE default tape device to use instead of
/dev/rst0
/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
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.
stty(1), fts(3), rcmd(3), st(4), fstab(5), restore(8),
rmt(8)
A dump command appeared in Version 5 AT&T UNIX.
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 flag 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 required
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 provided
more assistance for the operator running restore(8).
OpenBSD 3.6 June 4, 1997
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