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NAME    [Toc]    [Back]

     dump, rdump -- file system backup

SYNOPSIS    [Toc]    [Back]

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

     rdump is an alternate name for dump.

     (The 4.3BSD option syntax is implemented for backward compatibility, but
     is not documented here.)

DESCRIPTION    [Toc]    [Back]

     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
     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 -B options.  By
     default, the same output file name is used for each volume after prompting
 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 standard
 entry in /etc/fstab).

     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
	     default 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 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 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
	     always 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 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 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.

     -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
	     incremental backups omit such files but full backups retain them.

     -L      This option is to notify dump that it is dumping a live file system.
  To obtain a consistent dump image, dump takes a snapshot of
	     the file system in the .snap directory in the root of the
	     filesystem being dumped and then does a dump of the snapshot.
	     The snapshot is removed when the dump is complete.  If the .snap
	     directory does not exist in the root of the filesystem being
	     dumped, the dump will fail.  This problem can be corrected by
	     creating a .snap directory in the root of the filesystem to be
	     dumped; its owner should be root, its group should be operator,
	     and its mode should be 0770.

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

     -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 specific
 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
	     information 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 highlights
 those file systems that should be dumped.  If the -W
	     option is set, all other options are ignored, and dump exits

     -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
     error (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 intervals
 (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 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.

ENVIRONMENT    [Toc]    [Back]

     TAPE  Device from which to read backup.

     RMT   Pathname of the remote rmt(8) program.

FILES    [Toc]    [Back]

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

SEE ALSO    [Toc]    [Back]

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

DIAGNOSTICS    [Toc]    [Back]

     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.

BUGS    [Toc]    [Back]

     Fewer than 32 read errors on the file system are ignored, though all
     errors 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 dump.

     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 provided
 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.

HISTORY    [Toc]    [Back]

     A dump utility appeared in Version 6 AT&T UNIX.

FreeBSD 5.2.1			 March 1, 2002			 FreeBSD 5.2.1
[ Back ]
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