DUMP(8) OpenBSD System Manager's Manual DUMP(8)NAME
dump - filesystem backup
SYNOPSIS
dump [-0123456789acnuWw] [-B records] [-b blocksize] [-d density]
[-f file] [-h level] [-s feet] [-T date] files-to-dump
DESCRIPTION
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. 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.
dump works across networks, replacing the functionality of the old rdump
program (though dump may still be invoked as rdump). See the -f option
for more on writing backups to remote hosts.
Files can be marked with the ``nodump'' flag using chflags(1), settable
only by the file's owner or the superuser. Files with this flag set will
only be dumped during full backups. See also the -h option, below.
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.
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 I/O 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). See also the TAPE
environment variable, below.
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 (see above), 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.
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.
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.
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.
In the event of a catastrophic disk event, the time required to restore
all the necessary backup tapes or files to disk is dependent on the
levels of the dumps taken. A few methods of staggering incremental dumps
to either minimize backup effort or restore effort follow:
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 the level 0 dump, backups of active file systems are
taken on each day in a cycle of a week. Once a week, a level 1
dump is taken. The other days of the week a higher level dump
is done.
The following cycle needs at most three tapes to restore to a
given point in time, but the dumps at the end of the weekly
cycle will require more time and space:
1 2 2 2 2 2 2
This sequence requires at most eight tapes to restore, but the
size of the individual dumps will be smaller:
1 2 3 4 5 6 7
This sequence seeks a compromise between backup and restore
effort:
1 2 2 3 3 4 4
The weekly level 1 dumps should be done on a set of tapes that
is used cyclically. For the daily dumps a tape per day of the
week can be used.
o After several months or so, the daily and weekly tapes should
get rotated out of the dump cycle and fresh tapes brought in.
ENVIRONMENT
TAPE The default file to use instead of /dev/rst0. See also
-f, above.
FILES
/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
DIAGNOSTICS
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.
SEE ALSOchflags(1), stty(1), fts(3), rcmd(3), st(4), fstab(5), restore(8), rmt(8)HISTORY
A dump command appeared in Version 5 AT&T UNIX.
The 4.3BSD option syntax is implemented for backward compatibility but is
not documented here.
BUGS
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 4.9 January 26, 2008 OpenBSD 4.9
