Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
DUMP(8)			  BSD System Manager's Manual		       DUMP(8)

     dump, rdump -- file system	backup

     dump [-0123456789acLnrRSu]	[-B records] [-b blocksize] [-C	cachesize]
	  [-D dumpdates] [-d density] [-f file | -P pipecommand] [-h level]
	  [-s feet] [-T	date] filesystem
     dump -W | -w

     The dump utility 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	en-
     forced 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 -B options.	 By
     default, the same output file name	is used	for each volume	after prompt-
     ing the operator to change	media.

     The file system to	be dumped is specified by the argument filesystem as
     either its	device-special file or its mount point (if that	is in a	stan-
     dard entry	in /etc/fstab).

     dump may also be invoked as rdump.	 The 4.3BSD option syntax is imple-
     mented for	backward compatibility,	but is not documented here.

     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 any	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 fits
	     best for most modern tape drives.	Use of this option is particu-
	     larly 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 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.

     -b	blocksize
	     The number	of kilobytes per output	block.	The default block size
	     is	10.

     -C	cachesize
	     Specify the cache size in megabytes.  This	will greatly improve
	     performance at the	cost of	dump possibly not noticing changes in
	     the file system between passes.  It is recommended	that you al-
	     ways use this option when dumping a snapshot.  Beware that	dump
	     forks, and	the actual memory use may be larger than the specified
	     cache size.  The recommended cache	size is	between	8 and 32

     -c	     Change the	defaults for use with a	cartridge tape drive, with a
	     density of	8000 bpi, and a	length of 1700 feet.

     -D	dumpdates
	     Specify an	alternate path to the dumpdates	file.  The default is

     -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/sa0 (a tape drive), /dev/fd1 (a floppy disk drive), an ordi-
	     nary 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 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).  The default path	name of	the
	     remote rmt(8) program is /etc/rmt;	this can be overridden by the
	     environment variable RMT.

     -P	pipecommand
	     Use popen(3) to execute the sh(1) script string defined by
	     pipecommand for the output	device of each volume.	This child
	     pipeline's	stdin (/dev/fd/0) is redirected	from the dump output
	     stream, and the environment variable DUMP_VOLUME is set to	the
	     current volume number being written.  After every volume, the
	     writer side of the	pipe is	closed and pipecommand is executed
	     again.  Subject to	the media size specified by -B,	each volume is
	     written in	this manner as if the output were a tape drive.

     -h	level
	     Honor the user "nodump" flag (UF_NODUMP) only for dumps at	or
	     above the given level.  The default honor level is	1, so that in-
	     cremental backups omit such files but full	backups	retain them.

     -L	     This option is to notify dump that	it is dumping a	live file sys-
	     tem.  To obtain a consistent dump image, dump takes a snapshot of
	     the file system in	the .snap 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 re-
	     moved when	the dump is complete.  This option is ignored for un-
	     mounted or	read-only file systems.	 If the	.snap directory	does
	     not exist in the root of the file system being dumped, a warning
	     will be issued and	the dump will revert to	the standard behavior.
	     This problem can be corrected by creating a .snap directory in
	     the root of the file system to be dumped; its owner should	be
	     "root", its group should be "operator", and its mode should be

     -n	     Whenever dump requires operator attention,	notify all operators
	     in	the group "operator" by	means similar to a wall(1).

     -r	     Be	rsync-friendly.	 Normally dump stores the date of the current
	     and prior dump in numerous	places throughout the dump.  These
	     scattered changes significantly slow down rsync or	another	incre-
	     mental file transfer program when they are	used to	update a re-
	     mote copy of a level 0 dump, since	the date changes for each
	     dump.  This option	sets both dates	to the epoch, permitting rsync
	     to	be much	more efficient when transferring a dump	file.

     -R	     Be	even more rsync-friendly.  This	option disables	the storage of
	     the actual	inode access time (storing it instead as the inode's
	     modified time).  This option permits rsync	to be even more	effi-
	     cient when	transferring dumps generated from filesystems with nu-
	     merous files which	are not	changing other than their access
	     times.  The -R option also	sets -r.

     -S	     Display an	estimate of the	backup size and	the number of tapes
	     required, and exit	without	actually performing the	dump.

     -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 the	dumpdates file.	 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	spe-
	     cific period of time.  The	-T option is mutually exclusive	from
	     the -u option.

     -u	     Update the	dumpdates file after a successful dump.	 The format of
	     the dumpdates file	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	dumpdates file may be edited to	change
	     any of the	fields,	if necessary.  The default path	for the
	     dumpdates file is /etc/dumpdates, but the -D option may be	used
	     to	change it.

     -W	     Tell the operator what file systems need to be dumped.  This in-
	     formation is gleaned from the files dumpdates and /etc/fstab.
	     The -W option causes dump to print	out, for each file system in
	     the dumpdates file	the most recent	dump date and level, and high-
	     lights those file systems that should be dumped.  If the -W op-
	     tion is set, all other options are	ignored, and dump exits	imme-

     -w	     Is	like -W, but prints only those file systems which need to be

     Directories and regular files which have their "nodump" flag (UF_NODUMP)
     set will be omitted along with everything under such directories, subject
     to	the -h option.

     The dump utility requires operator	intervention on	these conditions: end
     of	tape, end of dump, tape	write error, tape open error or	disk read er-
     ror (if there are more than a threshold of	32).  In addition to alerting
     all operators implied by the -n key, 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.

     The dump utility tells the	operator what is going on at periodic inter-
     vals (every 5 minutes, or promptly	after receiving	SIGINFO), 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/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

	   o   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 algo-
	       rithm, 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.

     TAPE  The file or device to dump to if the	-f option is not used.

     RMT   Pathname of the remote rmt(8) program.

     RSH   Pathname of a remote	shell program, if not rsh(1).

     /dev/sa0	     default tape unit to dump to
     /etc/dumpdates  dump date records (this can be changed; see the -D	op-
     /etc/fstab	     dump table: file systems and frequency
     /etc/group	     to	find group operator

     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.

     Dumps the /u file system to DVDs using growisofs.	Uses a 16MB cache,
     creates a snapshot	of the dump, and records the dumpdates file.

     /sbin/dump	-0u  -L	-C16 -B4589840 -P 'growisofs -Z	/dev/cd0=/dev/fd/0' /u

     Many, and verbose.

     chflags(1), fstab(5), restore(8), rmt(8)

     A dump utility appeared in	Version	4 AT&T UNIX.

     Fewer than	32 read	errors on the file system are ignored, though all er-
     rors 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 dump is
     running.  Since dumps are often done in an	unattended fashion using
     cron(8) jobs asking for Operator intervention would result	in the dump
     dying.  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 is written.

     The dump utility with the -W or -w	options	does not report	file systems
     that have never been recorded in the dumpdates file, even if listed in

     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(8).

     The dump utility cannot do	remote backups without being run as root, due
     to	its security history.  This will be fixed in a later version of
     FreeBSD.  Presently, it works if you set it setuid	(like it used to be),
     but this might constitute a security risk.

BSD				October	3, 2016				   BSD


Want to link to this manual page? Use this URL:

home | help