Explain some caveats with dump -m in the man page.
[dump.git] / dump / dump.8.in
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29 .\" $Id: dump.8.in,v 1.58 2005/06/01 13:44:35 stelian Exp $
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31 .TH DUMP 8 "version __VERSION__ of __DATE__" BSD "System management commands"
33 dump \- ext2/3 filesystem backup
35 .B dump
36 [\fB\-\fIlevel#\fR]
37 [\fB\-ackMnqSuv]
38 [\fB\-A \fIfile\fR]
39 [\fB\-B \fIrecords\fR]
40 [\fB\-b \fIblocksize\fR]
41 [\fB\-d \fIdensity\fR]
42 [\fB\-D \fIfile\fR]
43 [\fB\-e \fIinode numbers\fR]
44 [\fB\-E \fIfile\fR]
45 [\fB\-f \fIfile\fR]
46 [\fB\-F \fIscript\fR]
47 [\fB\-h \fIlevel\fR]
48 [\fB\-I \fInr errors\fR]
49 [\fB\-j\fIcompression level\fR]
50 [\fB\-L \fIlabel\fR]
51 [\fB\-Q \fIfile\fR]
52 [\fB\-s \fIfeet\fR]
53 [\fB\-T \fIdate\fR]
54 [\fB\-y\fR]
55 [\fB\-z\fIcompression level\fR]
56 .I files-to-dump
57 .PP
58 .B dump
59 [\fB\-W \fR| \fB\-w\fR]
61 .B Dump
62 examines files on an ext2/3 filesystem and determines which files need to be
63 backed up. These files are copied to the given disk, tape or other storage
64 medium for safe keeping (see the
65 .B \-f
66 option below for doing remote backups). A dump that is larger than the output
67 medium is broken into multiple volumes. On most media the size is determined by
68 writing until an end-of-media indication is returned.
69 .PP
70 On media that cannot reliably return an end-of-media indication (such as some
71 cartridge tape drives), each volume is of a fixed size; the actual size is
72 determined by specifying cartridge media, or via the tape size, density and/or
73 block count options below. By default, the same output file name is used for
74 each volume after prompting the operator to change media.
75 .PP
76 .I files-to-dump
77 is either a mountpoint of a filesystem or a list of files and directories to be
78 backed up as a subset of a filesystem. In the former case, either the path to a
79 mounted filesystem or the device of an unmounted filesystem can be used. In the
80 latter case, certain restrictions are placed on the backup:
81 .B \-u
82 is not allowed, the only dump level that is supported is
83 .B 0
84 and all the files and directories must reside on the same filesystem.
86 The following options are supported by
87 .B dump:
88 .TP
89 .BI \-level#
90 The dump level (any integer). A level 0, full backup, guarantees the
91 entire file system is copied (but see also the
92 .B \-h
93 option below). A level number above 0, incremental backup, tells
94 .B dump
95 to
96 copy all files new or modified since the last dump of a lower level. The
97 default level is 9. Historically only levels 0 to 9 were usable in
98 dump, this version is able to understand any integer as a dump level.
99 .TP
100 .BI \-a
101 \*(lqauto-size\*(rq. Bypass all tape length calculations, and write until an
102 end-of-media indication is returned. This works best for most modern tape
103 drives, and is the default. Use of this option is particularly recommended when
104 appending to an existing tape, or using a tape drive with hardware compression
105 (where you can never be sure about the compression ratio).
106 .TP
107 .BI \-A " archive_file"
108 Archive a dump table-of-contents in the specified
109 .I archive_file
110 to be used by
111 .BR restore (8)
112 to determine whether a file is in the dump file that is being restored.
113 .TP
114 .BI \-b " blocksize"
115 The number of kilobytes per dump record. The default blocksize is 10,
116 unless the
117 .B \-d
118 option has been used to specify a tape density of 6250BPI or more,
119 in which case the default blocksize is 32. Th maximal value is 1024.
120 Note however that, since the IO system slices all requests into chunks
121 of
123 (which can be as low as 64kB), you can experience problems with
124 .BR dump (8)
125 and
126 .BR restore (8)
127 when using a higher value, depending on your kernel and/or libC versions.
128 .TP
129 .BI \-B " records"
130 The number of 1 kB blocks per volume. Not normally required, as
131 .B dump
132 can detect end-of-media. When the specified size is reached,
133 .B dump
134 waits for you to change the volume. This option overrides the calculation of
135 tape size based on length and density. If compression is on this limits the
136 size of the compressed output per volume. Multiple values may be given
137 as a single argument separated by commas. Each value will be used for one
138 dump volume in the order listed; if
139 .B dump
140 creates more volumes than the
141 number of values given, the last value will be used for the remaining
142 volumes. This is useful for filling up already partially filled media
143 (and then continuing with full size volumes on empty media) or mixing media
144 of different sizes.
145 .TP
146 .BI \-c
147 Change the defaults for use with a cartridge tape drive, with a density of 8000
148 bpi, and a length of 1700 feet. Specifying a cartridge drive overrides the
149 end-of-media detection.
150 .TP
151 .BI \-d " density"
152 Set tape density to
153 .IR density .
154 The default is 1600BPI. Specifying a tape density overrides the end-of-media
155 detection.
156 .TP
157 .BI \-D " file"
158 Set the path name of the file storing the information about the previous
159 full and incremental dumps. The default location is
160 .IR __DUMPDATES__ .
161 .TP
162 .BI \-e " inodes"
163 Exclude
164 .I inodes
165 from the dump. The
166 .I inodes
167 parameter is a comma separated list of inode numbers (you can use
168 .BR stat (1)
169 to find the inode number for a file or directory).
170 .TP
171 .BI \-E " file"
172 Read list of inodes to be excluded from the dump from the text file
173 .IR file .
174 The file
175 .I file
176 should be an ordinary file containing inode numbers separated by newlines.
177 .TP
178 .BI \-f " file"
179 Write the backup to
180 .IR file ;
181 .I file
182 may be a special device file like
183 .I /dev/st0
184 (a tape drive),
185 .I /dev/rsd1c
186 (a floppy disk drive), an ordinary file, or
187 .I \-
188 (the standard output). Multiple file names may be given as a single argument
189 separated by commas. Each file will be used for one dump volume in the order
190 listed; if the dump requires more volumes than the number of names given,
191 the last file name will used for all remaining volumes after prompting for
192 media changes. If the name of the file is of the form
193 .I host:file
194 or
195 .I user@host:file
196 .B dump
197 writes to the named file on the remote host (which should already
198 exist, dump doesn't create a new remote file) using
199 .BR rmt (8).
200 The default path name of the remote
201 .BR rmt (8)
202 program is
203 .IR /etc/rmt ;
204 this can be overridden by the environment variable
205 .BR RMT .
206 .TP
207 .BI \-F " script"
208 Run script at the end of each tape (except for the last one).
209 The device name and the current volume number are passed on the
210 command line. The script must return 0 if
211 .B dump
212 should continue without asking the user to change the tape, 1 if
213 .B dump
214 should continue but ask the user to change the tape. Any other exit code will
215 cause
216 .B dump
217 to abort. For security reasons,
218 .B dump
219 reverts back to the real user ID and the real group ID before running the
220 script.
221 .TP
222 .BI \-h " level"
223 Honor the user
224 .B nodump
225 flag
227 only for dumps at or above the given
228 .IR level .
229 The default honor level is 1, so that incremental backups omit such files but
230 full backups retain them.
231 .TP
232 .BI \-I " nr errors"
233 By default,
234 .B dump
235 will ignore the first 32 read errors on the file system before asking for
236 operator intervention. You can change this using this flag to any value. This
237 is useful when running
238 .B dump
239 on an active filesystem where read errors simply indicate an inconsistency
240 between the mapping and dumping passes.
241 .IP
242 A value of 0 means that all read errors will be ignored.
243 .TP
244 .BI \-j "compression level"
245 Compress every block to be written on the tape using bzlib library. This option
246 will work only when dumping to a file or pipe or, when dumping to a tape drive,
247 if the tape drive is capable of writing variable length blocks. You will need
248 at least the 0.4b24 version of
249 .B restore
250 in order to extract compressed tapes. Tapes written using compression will not
251 be compatible with the BSD tape format. The (optional) parameter specifies the
252 compression level bzlib will use. The default compression level is 2. If the
253 optional parameter is specified, there should be no white space between the
254 option letter and the parameter.
255 .TP
256 .BI \-k
257 Use Kerberos authentication to talk to remote tape servers. (Only available if
258 this option was enabled when
259 .B dump
260 was compiled.)
261 .TP
262 .BI \-L " label"
263 The user-supplied text string
264 .I label
265 is placed into the dump header, where tools like
266 .BR restore (8)
267 and
268 .BR file (8)
269 can access it. Note that this label is limited to be at most
271 (currently 16) characters, which must include the terminating \e0.
272 .TP
273 .BI \-m
274 If this flag is specified,
275 .B dump
276 will optimise the output for inodes having been changed but not modified since
277 the last dump ('changed' and 'modified' have the meaning defined in
278 .BR stat (2)
279 ). For those inodes,
280 .B dump
281 will save only the metadata, instead of saving the entire inode contents.
282 Inodes which are either directories or have been modified since the last dump
283 are saved in a regular way. Uses of this flag must be consistent, meaning that
284 either every dump in an incremental dump set have the flag, or no one has it.
285 .IP
286 If you use this option, be aware that many programs that unpack
287 files from archives (e.g. tar, rpm, unzip, dpkg) may set files'
288 mtimes to dates in the past. Files installed in this way may not be
289 dumped correctly using "dump -m" if the modified mtime is earlier
290 than the previous level dump.
291 .IP
292 Tapes written using such 'metadata only' inodes will not be compatible with the
293 BSD tape format or older versions of
294 .B restore.
295 .TP
296 .BI \-M
297 Enable the multi-volume feature. The name specified with
298 .B f
299 is treated as a prefix and
300 .B dump
301 writes in sequence to
302 .I <prefix>001, <prefix>002
303 etc. This can be useful when dumping to files on an ext2 partition, in order to
304 bypass the 2GB file size limitation.
305 .TP
306 .BI \-n
307 Whenever
308 .B dump
309 requires operator attention, notify all operators in the group
310 .B operator
311 by means similar to a
312 .BR wall (1).
313 .TP
314 .BI \-q
315 Make
316 .B dump
317 abort immediately whenever operator attention is required, without prompting in
318 case of write errors, tape changes etc.
319 .TP
320 .BI \-Q " file"
321 Enable the Quick File Access support. Tape positions for each inode are stored
322 into the file
323 .I file
324 which is used by
325 .B restore
326 (if called with parameter
327 .B \-Q
328 and the filename) to directly position the tape at the file
329 .B restore
330 is currently working on. This saves hours when restoring single files from
331 large backups, saves the tapes and the drive's head.
332 .IP
333 It is recommended to set up the st driver to return logical tape positions
334 rather than physical before calling
335 .B dump/restore
336 with parameter
337 .BR \-Q .
338 Since not all tape devices support physical tape positions those tape devices
339 return an error during
340 .B dump/restore
341 when the st driver is set to the default physical setting. Please see the
342 .BR st (4)
343 man page, option
345 , or the
346 .BR mt (1)
347 man page, on how to set the driver to return logical tape positions.
348 .IP
349 Before calling
350 .B restore
351 with parameter
352 .BR \-Q ,
353 always make sure the st driver is set to return the same type of tape position
354 used during the call to
355 .BR dump .
356 Otherwise
357 .B restore
358 may be confused.
359 .IP
360 This option can be used when dumping to local tapes (see above) or to local
361 files.
362 .TP
363 .BI \-s " feet"
364 Attempt to calculate the amount of tape needed at a particular density. If this
365 amount is exceeded,
366 .B dump
367 prompts for a new tape. It is recommended to be a bit conservative on this
368 option. The default tape length is 2300 feet. Specifying the tape size
369 overrides end-of-media detection.
370 .TP
371 .BI \-S
372 Size estimate. Determine the amount of space that is needed to perform the dump
373 without actually doing it, and display the estimated number of bytes it will
374 take. This is useful with incremental dumps to determine how many volumes of
375 media will be needed.
376 .TP
377 .BI \-T " date"
378 Use the specified date as the starting time for the dump instead of the time
379 determined from looking in
380 .I __DUMPDATES__ .
381 The format of
382 .I date
383 is the same as that of
384 .BR ctime (3)
385 followed by an rfc822 timezone specification: either a plus or minus sign
386 followed by two digits for the number of hours and two digits for the minutes.
387 For example, -0800 for eight hours west of Greenwich or +0230 for two hours
388 and a half east of Greenwich. This timezone offset takes into account
389 daylight savings time (if applicable to the timezone): UTC offsets
390 when daylight savings time is in effect will be different than offsets
391 when daylight savings time is not in effect. For backward
392 compatibility, if no timezone is specified, a local time is assumed.
393 This option is useful for automated dump scripts that wish to dump over a
394 specific period of time. The
395 .B \-T
396 option is mutually exclusive from the
397 .B \-u
398 option.
399 .TP
400 .BI \-u
401 Update the file
402 .I __DUMPDATES__
403 after a successful dump. The format of
404 .I __DUMPDATES__
405 is readable by people, consisting of one free format record per line:
406 filesystem name, increment level and
407 .BR ctime (3)
408 format dump date followed by a rfc822 timezone specification (see the
409 .B \-u
410 option for details). If no timezone offset is specified, times are interpreted
411 as local. Whenever the file is written, all dates in the file are converted
412 to the local time zone, without changing the UTC times. There
413 may be only one entry per filesystem at each level. The file
414 .I __DUMPDATES__
415 may be edited to change any of the fields, if necessary.
416 .TP
417 .BI \-v
418 The
419 .B \-v
420 (verbose) makes
421 .B dump
422 to print extra information which could be helpful in debug sessions.
423 .TP
424 .BI \-W
425 .B Dump
426 tells the operator what file systems need to be dumped. This information is
427 gleaned from the files
428 .I __DUMPDATES__
429 and
430 .IR /etc/fstab .
431 The
432 .B \-W
433 option causes
434 .B dump
435 to print out, for all file systems in
436 .I __DUMPDATES__ ,
437 and regognized file systems in
438 .I /etc/mtab
439 and
440 .IR /etc/fstab .
441 the most recent dump date and level, and highlights those that should be
442 dumped. If the
443 .B \-W
444 option is set, all other options are ignored, and
445 .B dump
446 exits immediately.
447 .TP
448 .BI \-w
449 Is like
450 .BR \-W ,
451 but prints only recognized filesystems in
452 .I /etc/mtab
453 and
454 .I /etc/fstab
455 which need to be dumped.
456 .TP
457 .BI \-y
458 Compress every block to be written to the tape using the lzo library.
459 This doesn't compress as well as the zlib library but it's much faster.
460 This option will work only when dumping to a file or pipe or, when dumping to
461 a tape drive, if the tape drive is capable of writing variable length blocks.
462 You will need at least the 0.4b34 version of
463 .B restore
464 in order to extract compressed tapes. Tapes written using compression will not
465 be compatible with the BSD tape format.
466 .TP
467 .BI \-z "compression level"
468 Compress every block to be written on the tape using zlib library. This option
469 will work only when dumping to a file or pipe or, when dumping to a tape drive,
470 if the tape drive is capable of writing variable length blocks. You will need
471 at least the 0.4b22 version of
472 .B restore
473 in order to extract compressed tapes. Tapes written using compression will not
474 be compatible with the BSD tape format. The (optional) parameter specifies the
475 compression level zlib will use. The default compression level is 2. If the
476 optional parameter is specified, there should be no white space between the
477 option letter and the parameter.
478 .PP
479 .B Dump
480 requires operator intervention on these conditions: end of tape, end of dump,
481 tape write error, tape open error or disk read error (if there is more than a
482 threshold of nr errors). In addition to alerting all operators implied by the
483 .B \-n
484 key,
485 .B dump
486 interacts with the operator on dump's control terminal at times when
487 .B dump
488 can no longer proceed, or if something is grossly wrong. All questions
489 .B dump
490 poses
491 .I must
492 be answered by typing \*(lqyes\*(rq or \*(lqno\*(rq, appropriately.
493 .PP
494 Since making a dump involves a lot of time and effort for full dumps,
495 .B dump
496 checkpoints itself at the start of each tape volume. If writing that volume
497 fails for some reason,
498 .B dump
499 will, with operator permission, restart itself from the checkpoint after the
500 old tape has been rewound and removed, and a new tape has been mounted.
501 .PP
502 .B Dump
503 tells the operator what is going on at periodic intervals, including usually
504 low estimates of the number of blocks to write, the number of tapes it will
505 take, the time to completion, and the time to the tape change. The output is
506 verbose, so that others know that the terminal controlling
507 .B dump
508 is busy, and will be for some time.
509 .PP
510 In the event of a catastrophic disk event, the time required to restore all the
511 necessary backup tapes or files to disk can be kept to a minimum by staggering
512 the incremental dumps. An efficient method of staggering incremental dumps to
513 minimize the number of tapes follows:
514 .IP \(em
515 Always start with a level 0 backup, for example:
516 .RS 14
517 .B /sbin/dump -0u -f /dev/st0 /usr/src
518 .RE
519 .IP
520 This should be done at set intervals, say once a month or once every two months,
521 and on a set of fresh tapes that is saved forever.
522 .IP \(em
523 After a level 0, dumps of active file systems are taken on a daily basis, using
524 a modified Tower of Hanoi algorithm, with this sequence of dump levels:
525 .RS 14
526 .B 3 2 5 4 7 6 9 8 9 9 ...
527 .RE
528 .IP
529 For the daily dumps, it should be possible to use a fixed number of tapes for
530 each day, used on a weekly basis. Each week, a level 1 dump is taken, and the
531 daily Hanoi sequence repeats beginning with 3. For weekly dumps, another fixed
532 set of tapes per dumped file system is used, also on a cyclical basis.
533 .PP
534 After several months or so, the daily and weekly tapes should get rotated out
535 of the dump cycle and fresh tapes brought in.
536 .PP
537 (The 4.3BSD option syntax is implemented for backward compatibility but is not
538 documented here.)
540 .TP
541 .B TAPE
542 If no
543 .B \-f
544 option was specified,
545 .B dump
546 will use the device specified via
547 .B TAPE
548 as the dump device.
549 .B TAPE
550 may be of the form
551 .IR tapename ,
552 .IR host:tapename ,
553 or
554 .IR user@host:tapename .
555 .TP
556 .B RMT
557 The environment variable
558 .B RMT
559 will be used to determine the pathname of the remote
560 .BR rmt (8)
561 program.
562 .TP
563 .B RSH
564 .B Dump
565 uses the contents of this variable to determine the name of the remote shell
566 command to use when doing remote backups (rsh, ssh etc.). If this variable is
567 not set,
568 .BR rcmd (3)
569 will be used, but only root will be able to do remote backups.
571 .TP
572 .I /dev/st0
573 default tape unit to dump to
574 .TP
575 .I __DUMPDATES__
576 dump date records
577 .TP
578 .I /etc/fstab
579 dump table: file systems and frequency
580 .TP
581 .I /etc/mtab
582 dump table: mounted file systems
583 .TP
584 .I /etc/group
585 to find group
586 .I operator
588 .BR fstab (5),
589 .BR restore (8),
590 .BR rmt (8)
592 Many, and verbose.
594 The format of the
595 .I __DUMPDATES__
596 file has changed in release 0.4b34, however, the file will be read
597 correctly with either pre-0.4b34 or 0.4b34 and later versions of
598 .B dump
599 provided that the machine on which
600 .B dump
601 is run did not change timezones (which should be a fairly rare occurence).
603 .B Dump
604 exits with zero status on success. Startup errors are indicated with an exit
605 code of 1; abnormal termination is indicated with an exit code of 3.
606 .SH BUGS
607 It might be considered a bug that this version of dump can only handle ext2/3
608 filesystems. Specifically, it does not work with FAT filesystems.
609 .PP
610 Fewer than 32 read errors (change this with
611 .BR \-I )
612 on the filesystem are ignored. If noticing read errors is important, the output
613 from dump can be parsed to look for lines that contain the text 'read error'.
614 .PP
615 When a read error occurs,
616 .B dump
617 prints out the corresponding physical disk block and sector number and the
618 ext2/3 logical block number. It doesn't print out the corresponing file name or
619 even the inode number. The user has to use
620 .BR debugfs (8),
621 commands
622 .B ncheck
623 and
624 .B icheck
625 to translate the
626 .B ext2blk
627 number printed out by
628 .B dump
629 into an inode number, then into a file name.
630 .PP
631 Each reel requires a new process, so parent processes for reels already written
632 just hang around until the entire tape is written.
633 .PP
634 The estimated number of tapes is not correct if compression is on.
635 .PP
636 It would be nice if
637 .B dump
638 knew about the dump sequence, kept track of the tapes scribbled on, told the
639 operator which tape to mount when, and provided more assistance for the
640 operator running
641 .BR restore .
642 .PP
643 .B Dump
644 cannot do remote backups without being run as root, due to its security history.
645 Presently, it works if you set it setuid (like it used to be), but this might
646 constitute a security risk. Note that you can set
647 .B RSH
648 to use a remote shell program instead.
650 The
651 .B dump/restore
652 backup suite was ported to Linux's Second Extended File System by Remy Card
653 <card@Linux.EU.Org>. He maintained the initial versions of
654 .B dump
655 (up and including 0.4b4, released in january 1997).
656 .PP
657 Starting with 0.4b5, the new maintainer is Stelian Pop <stelian@popies.net>.
659 The
660 .B dump/restore
661 backup suite is available from <http://dump.sourceforge.net>
663 A
664 .B dump
665 command appeared in
666 .B Version 6 AT&T UNIX.