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29 .\" @(#)dump.8 8.3 (Berkeley) 5/1/95
38 .Nd file system backup
41 .Op Fl 0123456789acLnrRSu
47 .Op Fl f Ar file | Fl P Ar pipecommand
57 utility examines files
59 and determines which files
62 are copied to the given disk, tape or other
63 storage medium for safe keeping (see the
65 option below for doing remote backups).
66 A dump that is larger than the output medium is broken into
68 On most media the size is determined by writing until an
69 end-of-media indication is returned.
75 On media that cannot reliably return an end-of-media indication
76 (such as some cartridge tape drives)
77 each volume is of a fixed size;
78 the actual size is determined by the tape size and density and/or
81 By default, the same output file name is used for each volume
82 after prompting the operator to change media.
84 The file system to be dumped is specified by the argument
86 as either its device-special file or its mount point
87 (if that is in a standard entry in
91 may also be invoked as
95 option syntax is implemented for backward compatibility, but
96 is not documented here.
98 The following options are supported by
103 A level 0, full backup,
104 guarantees the entire file system is copied
108 A level number above 0,
111 copy all files new or modified since the
112 last dump of any lower level.
113 The default level is 0.
116 Bypass all tape length considerations, and enforce writing
117 until an end-of-media indication is returned.
118 This fits best for most modern tape drives.
119 Use of this option is particularly
120 recommended when appending to an existing tape, or using a tape
121 drive with hardware compression (where you can never be sure about
122 the compression ratio).
124 The number of kilobytes per output volume, except that if it is
125 not an integer multiple of the output block size,
126 the command uses the next smaller such multiple.
127 This option overrides the calculation of tape size
128 based on length and density.
129 .It Fl b Ar blocksize
130 The number of kilobytes per output block.
131 The default block size is 10.
132 .It Fl C Ar cachesize
133 Specify the cache size in megabytes.
134 This will greatly improve performance
137 possibly not noticing changes in the file system between passes.
139 recommended that you always use this option when dumping a snapshot.
142 forks, and the actual memory use may be larger than the specified cache
144 The recommended cache size is between 8 and 32 (megabytes).
146 Change the defaults for use with a cartridge tape drive, with a density
147 of 8000 bpi, and a length of 1700 feet.
148 .It Fl D Ar dumpdates
149 Specify an alternate path to the
157 The default is 1600BPI.
162 may be a special device file
167 (a floppy disk drive),
171 (the standard output).
172 Multiple file names may be given as a single argument separated by commas.
173 Each file will be used for one dump volume in the order listed;
174 if the dump requires more volumes than the number of names given,
175 the last file name will used for all remaining volumes after prompting
177 If the name of the file is of the form
182 writes to the named file on the remote host using
184 The default path name of the remote
187 .\" rmt path, is the path on the remote host
189 this can be overridden by the environment variable
191 .It Fl P Ar pipecommand
196 script string defined by
198 for the output device of each volume.
199 This child pipeline's
202 is redirected from the
204 output stream, and the environment variable
206 is set to the current volume number being written.
207 After every volume, the writer side of the pipe is closed and
210 Subject to the media size specified by
212 each volume is written in this manner as if the output were a tape drive.
218 only for dumps at or above the given
220 The default honor level is 1,
221 so that incremental backups omit such files
222 but full backups retain them.
224 This option is to notify
226 that it is dumping a live file system.
227 To obtain a consistent dump image,
229 takes a snapshot of the file system in the
231 directory in the root of the file system being dumped and
232 then does a dump of the snapshot.
233 The snapshot is unlinked as soon as the dump starts, and
234 is thus removed when the dump is complete.
235 This option is ignored for unmounted or read-only file systems.
238 directory does not exist in the root of the file system being dumped,
239 a warning will be issued and the
241 will revert to the standard behavior.
242 This problem can be corrected by creating a
244 directory in the root of the file system to be dumped;
249 and its mode should be
254 requires operator attention,
255 notify all operators in the group
257 by means similar to a
261 Normally dump stores the date of the current
262 and prior dump in numerous places throughout the dump.
263 These scattered changes significantly slow down rsync or
264 another incremental file transfer program when they are
265 used to update a remote copy of a level 0 dump,
266 since the date changes for each dump.
267 This option sets both dates to the epoch, permitting
268 rsync to be much more efficient when transferring a dump file.
270 Be even more rsync-friendly.
271 This option disables the storage of the actual inode access time
272 (storing it instead as the inode's modified time).
273 This option permits rsync to be even more efficient
274 when transferring dumps generated from filesystems with numerous files
275 which are not changing other than their access times.
281 Display an estimate of the backup size and the number of
282 tapes required, and exit without actually performing the dump.
284 Attempt to calculate the amount of tape needed
285 at a particular density.
286 If this amount is exceeded,
288 prompts for a new tape.
289 It is recommended to be a bit conservative on this option.
290 The default tape length is 2300 feet.
292 Use the specified date as the starting time for the dump
293 instead of the time determined from looking in
297 The format of date is the same as that of
299 This option is useful for automated dump scripts that wish to
300 dump over a specific period of time.
303 option is mutually exclusive from the
310 after a successful dump.
315 is readable by people, consisting of one
316 free format record per line:
322 There may be only one entry per file system at each level.
326 may be edited to change any of the fields,
328 The default path for the
334 option may be used to change it.
336 Tell the operator what file systems need to be dumped.
337 This information is gleaned from the files
345 to print out, for each file system in
349 the most recent dump date and level,
350 and highlights those file systems that should be dumped.
353 option is set, all other options are ignored, and
359 but prints only those file systems which need to be dumped.
362 Directories and regular files which have their
366 set will be omitted along with everything under such directories,
373 utility requires operator intervention on these conditions:
378 disk read error (if there are more than a threshold of 32).
379 In addition to alerting all operators implied by the
383 interacts with the operator on
385 control terminal at times when
387 can no longer proceed,
388 or if something is grossly wrong.
393 be answered by typing
399 Since making a dump involves a lot of time and effort for full dumps,
401 checkpoints itself at the start of each tape volume.
402 If writing that volume fails for some reason,
405 with operator permission,
406 restart itself from the checkpoint
407 after the old tape has been rewound and removed,
408 and a new tape has been mounted.
412 utility tells the operator what is going on at periodic intervals
413 (every 5 minutes, or promptly after receiving
415 including usually low estimates of the number of blocks to write,
416 the number of tapes it will take, the time to completion, and
417 the time to the tape change.
418 The output is verbose,
419 so that others know that the terminal
423 and will be for some time.
425 In the event of a catastrophic disk event, the time required
426 to restore all the necessary backup tapes or files to disk
427 can be kept to a minimum by staggering the incremental dumps.
428 An efficient method of staggering incremental dumps
429 to minimize the number of tapes follows:
430 .Bl -bullet -offset indent
432 Always start with a level 0 backup, for example:
433 .Bd -literal -offset indent
434 /sbin/dump -0u -f /dev/nsa0 /usr/src
437 This should be done at set intervals, say once a month or once every two months,
438 and on a set of fresh tapes that is saved forever.
440 After a level 0, dumps of active file systems (file systems with files
441 that change, depending on your partition layout some file systems may
442 contain only data that does not change) are taken on a daily basis,
443 using a modified Tower of Hanoi algorithm,
444 with this sequence of dump levels:
445 .Bd -literal -offset indent
446 3 2 5 4 7 6 9 8 9 9 ...
449 For the daily dumps, it should be possible to use a fixed number of tapes
450 for each day, used on a weekly basis.
451 Each week, a level 1 dump is taken, and
452 the daily Hanoi sequence repeats beginning with 3.
453 For weekly dumps, another fixed set of tapes per dumped file system is
454 used, also on a cyclical basis.
457 After several months or so, the daily and weekly tapes should get
458 rotated out of the dump cycle and fresh tapes brought in.
460 .Bl -tag -width ".Ev TAPE"
464 or device to dump to if the
468 Pathname of the remote
472 Pathname of a remote shell program, if not
476 .Bl -tag -width /etc/dumpdates -compact
478 default tape unit to dump to
479 .It Pa /etc/dumpdates
481 (this can be changed;
486 dump table: file systems and frequency
492 Dump exits with zero status on success.
493 Startup errors are indicated with an exit code of 1;
494 abnormal termination is indicated with an exit code of 3.
498 file system to DVDs using
500 Uses a 16MB cache, creates a snapshot of the dump, and records the
504 /sbin/dump -0u -L -C16 -B4589840 -P 'growisofs -Z /dev/cd0=/dev/fd/0' /u
519 Fewer than 32 read errors on the file system are ignored, though all
520 errors will generate a warning message.
521 This is a bit of a compromise.
522 In practice, it is possible to generate read errors when doing dumps
523 on mounted partitions if the file system is being modified while the
526 Since dumps are often done in an unattended fashion using
528 jobs asking for Operator intervention would result in the
531 However, there is nothing wrong with a dump tape written when this sort
532 of read error occurs, and there is no reason to terminate the
535 Each reel requires a new process, so parent processes for
536 reels already written just hang around until the entire tape
545 options does not report file systems that have never been recorded
554 knew about the dump sequence,
555 kept track of the tapes scribbled on,
556 told the operator which tape to mount when,
557 and provided more assistance
558 for the operator running
563 utility cannot do remote backups without being run as root, due to its
565 This will be fixed in a later version of
567 Presently, it works if you set it setuid (like it used to be), but this
568 might constitute a security risk.