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  49 .TH DD 1M "Dec 12, 2014"
  50 .SH NAME
  51 dd \- convert and copy a file
  52 .SH SYNOPSIS
  53 .LP
  54 .nf
  55 \fB/usr/bin/dd\fR [\fIoperand=value\fR]...
  56 .fi
  57 
  58 .SH DESCRIPTION
  59 .LP
  60 The \fBdd\fR utility copies the specified input file to the specified output
  61 with possible conversions. The standard input and output are used by default.
  62 The input and output block sizes may be specified to take advantage of raw
  63 physical I/O. Sizes are specified in bytes; a number may end with \fBk\fR,
  64 \fBb\fR, or \fBw\fR to specify multiplication by 1024, 512, or 2, respectively.
  65 Numbers may also be separated by \fBx\fR to indicate multiplication.
  66 .sp
  67 .LP
  68 The \fBdd\fR utility reads the input one block at a time, using the specified
  69 input block size. \fBdd\fR then processes the block of data actually returned,
  70 which could be smaller than the requested block size. \fBdd\fR applies any
  71 conversions that have been specified and writes the resulting data to the
  72 output in blocks of the specified output block size.
  73 .sp
  74 .LP
  75 \fBcbs\fR is used only if \fBascii\fR, \fBasciib\fR, \fBunblock\fR,
  76 \fBebcdic\fR, \fBebcdicb\fR, \fBibm\fR, \fBibmb\fR, or \fBblock\fR conversion
  77 is specified. In the first two cases, \fBcbs\fR characters are copied into the
  78 conversion buffer, any specified character mapping is done, trailing blanks are
  79 trimmed, and a \fBNEWLINE\fR is added before sending the line to output. In the
  80 last three cases, characters up to \fBNEWLINE\fR are read into the conversion
  81 buffer and blanks are added to make up an output record of size \fBcbs\fR.
  82 \fBASCII\fR files are presumed to contain \fBNEWLINE\fR characters. If
  83 \fBcbs\fR is unspecified or \fB0\fR, the \fBascii\fR, \fBasciib\fR,
  84 \fBebcdic\fR, \fBebcdicb\fR, \fBibm\fR, and \fBibmb\fR options convert the
  85 character set without changing the input file's block structure. The
  86 \fBunblock\fR and \fBblock\fR options become a simple file copy.
  87 .sp
  88 .LP
  89 After completion, \fBdd\fR reports the number of whole and partial input and
  90 output blocks.
  91 .SH OPERANDS
  92 .LP
  93 The following operands are supported:
  94 .sp
  95 .ne 2
  96 .na
  97 \fB\fBif=\fR\fIfile\fR\fR
  98 .ad
  99 .sp .6
 100 .RS 4n
 101 Specifies the input path. Standard input is the default.
 102 .RE
 103 
 104 .sp
 105 .ne 2
 106 .na
 107 \fB\fBof=\fR\fIfile\fR\fR
 108 .ad
 109 .sp .6
 110 .RS 4n
 111 Specifies the output path. Standard output is the default. If the
 112 \fBseek=\fR\fBexpr\fR conversion is not also specified, the output file will be
 113 truncated before the copy begins, unless \fBconv=notrunc\fR is specified. If
 114 \fBseek=\fR\fBexpr\fR is specified, but \fBconv=notrunc\fR is not, the effect
 115 of the copy will be to preserve the blocks in the output file over which
 116 \fBdd\fR seeks, but no other portion of the output file will be preserved. (If
 117 the size of the seek plus the size of the input file is less than the previous
 118 size of the output file, the output file is shortened by the copy.)
 119 .RE
 120 
 121 .sp
 122 .ne 2
 123 .na
 124 \fB\fBibs=\fR\fIn\fR\fR
 125 .ad
 126 .sp .6
 127 .RS 4n
 128 Specifies the input block size in \fIn\fR bytes (default is \fB512\fR).
 129 .RE
 130 
 131 .sp
 132 .ne 2
 133 .na
 134 \fB\fBobs=\fR\fIn\fR\fR
 135 .ad
 136 .sp .6
 137 .RS 4n
 138 Specifies the output block size in \fIn\fR bytes (default is \fB512\fR).
 139 .RE
 140 
 141 .sp
 142 .ne 2
 143 .na
 144 \fB\fBbs=\fR\fIn\fR\fR
 145 .ad
 146 .sp .6
 147 .RS 4n
 148 Sets both input and output block sizes to \fIn\fR bytes, superseding \fBibs=\fR
 149 and \fBobs=\fR. If no conversion other than \fBsync\fR,\fB noerror\fR, and
 150 \fBnotrunc\fR is specified, each input block is copied to the output as a
 151 single block without aggregating short blocks.
 152 .RE
 153 
 154 .sp
 155 .ne 2
 156 .na
 157 \fB\fBcbs=\fR\fIn\fR\fR
 158 .ad
 159 .sp .6
 160 .RS 4n
 161 Specifies the conversion block size for \fBblock\fR and \fBunblock\fR in bytes
 162 by \fIn\fR (default is \fB0\fR). If \fBcbs=\fR is omitted or given a value of
 163 \fB0\fR, using \fBblock\fR or \fBunblock\fR produces unspecified results.
 164 .sp
 165 This option is used only if \fBASCII\fR or \fBEBCDIC\fR conversion is
 166 specified. For the \fBascii\fR and \fBasciib\fR operands, the input is handled
 167 as described for the \fBunblock\fR operand except that characters are converted
 168 to \fBASCII\fR before the trailing \fBSPACE\fR characters are deleted. For the
 169 \fBebcdic\fR, \fBebcdicb\fR, \fBibm\fR, and \fBibmb\fR operands, the input is
 170 handled as described for the \fBblock\fR operand except that the characters are
 171 converted to \fBEBCDIC\fR or IBM \fBEBCDIC\fR after the trailing \fBSPACE\fR
 172 characters are added.
 173 .RE
 174 
 175 .sp
 176 .ne 2
 177 .na
 178 \fB\fBfiles=\fR\fIn\fR\fR
 179 .ad
 180 .sp .6
 181 .RS 4n
 182 Copies and concatenates \fIn\fR input files before terminating (makes sense
 183 only where input is a magnetic tape or similar device).
 184 .RE
 185 
 186 .sp
 187 .ne 2
 188 .na
 189 \fB\fBskip=\fR\fIn\fR\fR
 190 .ad
 191 .sp .6
 192 .RS 4n
 193 Skips \fIn\fR input blocks (using the specified input block size) before
 194 starting to copy. On seekable files, the implementation reads the blocks or
 195 seeks past them. On non-seekable files, the blocks are read and the data is
 196 discarded.
 197 .RE
 198 
 199 .sp
 200 .ne 2
 201 .na
 202 \fB\fBiseek=\fR\fIn\fR\fR
 203 .ad
 204 .sp .6
 205 .RS 4n
 206 Seeks \fIn\fR blocks from beginning of input file before copying (appropriate
 207 for disk files, where \fBskip\fR can be incredibly slow).
 208 .RE
 209 
 210 .sp
 211 .ne 2
 212 .na
 213 \fB\fBoseek=\fR\fIn\fR\fR
 214 .ad
 215 .sp .6
 216 .RS 4n
 217 Seeks \fIn\fR blocks from beginning of output file before copying.
 218 .RE
 219 
 220 .sp
 221 .ne 2
 222 .na
 223 \fB\fBseek=\fR\fIn\fR\fR
 224 .ad
 225 .sp .6
 226 .RS 4n
 227 Skips \fIn\fR blocks (using the specified output block size) from beginning of
 228 output file before copying. On non-seekable files, existing blocks are read and
 229 space from the current end-of-file to the specified offset, if any, is filled
 230 with null bytes. On seekable files, the implementation seeks to the specified
 231 offset or reads the blocks as described for non-seekable files.
 232 .RE
 233 
 234 .sp
 235 .ne 2
 236 .na
 237 \fB\fBostride=\fR\fIn\fR\fR
 238 .ad
 239 .sp .6
 240 .RS 4n
 241 Writes every \fIn\fRth block (using the specified output block size) when
 242 writing output.  Skips \fIn\fR - 1 blocks after writing each record.
 243 .RE
 244 
 245 .sp
 246 .ne 2
 247 .na
 248 \fB\fBistride=\fR\fIn\fR\fR
 249 .ad
 250 .sp .6
 251 .RS 4n
 252 Reads every \fIn\fRth block (using the specified input block size) when
 253 reading input.  Skips \fIn\fR - 1 blocks after reading each record.
 254 .RE
 255 
 256 .sp
 257 .ne 2
 258 .na
 259 \fB\fBstride=\fR\fIn\fR\fR
 260 .ad
 261 .sp .6
 262 .RS 4n
 263 Reads every \fIn\fRth block (using the specified input block size) when
 264 reading input.  Skips \fIn\fR - 1 blocks after reading each record.  Also
 265 writes every \fIn\fRth block (using the specified output block size) when
 266 writing output.  Skips \fIn\fR - 1 blocks after writing each record.
 267 .RE
 268 
 269 .sp
 270 .ne 2
 271 .na
 272 \fB\fBcount=\fR\fIn\fR\fR
 273 .ad
 274 .sp .6
 275 .RS 4n
 276 Copies only \fIn\fR input blocks.
 277 .RE
 278 
 279 .sp
 280 .ne 2
 281 .na
 282 \fB\fBconv=\fR\fIvalue\fR[\fB,\fR\fIvalue\fR.\|.\|.\|]\fR
 283 .ad
 284 .sp .6
 285 .RS 4n
 286 Where \fIvalue\fRs are comma-separated symbols from the following list:
 287 .sp
 288 .ne 2
 289 .na
 290 \fB\fBascii\fR\fR
 291 .ad
 292 .RS 11n
 293 Converts \fBEBCDIC\fR to \fBASCII\fR.
 294 .RE
 295 
 296 .sp
 297 .ne 2
 298 .na
 299 \fB\fBasciib\fR\fR
 300 .ad
 301 .RS 11n
 302 Converts \fBEBCDIC\fR to \fBASCII\fR using \fBBSD\fR-compatible character
 303 translations.
 304 .RE
 305 
 306 .sp
 307 .ne 2
 308 .na
 309 \fB\fBebcdic\fR\fR
 310 .ad
 311 .RS 11n
 312 Converts \fBASCII\fR to \fBEBCDIC\fR. If converting fixed-length \fBASCII\fR
 313 records without NEWLINEs, sets up a pipeline with \fBdd conv=unblock\fR
 314 beforehand.
 315 .RE
 316 
 317 .sp
 318 .ne 2
 319 .na
 320 \fB\fBebcdicb\fR\fR
 321 .ad
 322 .RS 11n
 323 Converts \fBASCII\fR to \fBEBCDIC\fR using \fBBSD\fR-compatible character
 324 translations. If converting fixed-length \fBASCII\fR records without
 325 \fBNEWLINE\fRs, sets up a pipeline with \fBdd conv=unblock\fR beforehand.
 326 .RE
 327 
 328 .sp
 329 .ne 2
 330 .na
 331 \fB\fBibm\fR\fR
 332 .ad
 333 .RS 11n
 334 Slightly different map of \fBASCII\fR to \fBEBCDIC\fR. If converting
 335 fixed-length \fBASCII\fR records without \fBNEWLINE\fRs, sets up a pipeline
 336 with \fBdd conv=unblock\fR beforehand.
 337 .RE
 338 
 339 .sp
 340 .ne 2
 341 .na
 342 \fB\fBibmb\fR\fR
 343 .ad
 344 .RS 11n
 345 Slightly different map of \fBASCII\fR to \fBEBCDIC\fR using
 346 \fBBSD\fR-compatible character translations. If converting fixed-length
 347 \fBASCII\fR records without \fBNEWLINE\fRs, sets up a pipeline with \fBdd
 348 conv=unblock\fR beforehand.
 349 .RE
 350 
 351 The \fBascii\fR (or \fBasciib\fR), \fBebcdic\fR (or \fBebcdicb\fR), and
 352 \fBibm\fR (or \fBibmb\fR) values are mutually exclusive.
 353 .sp
 354 .ne 2
 355 .na
 356 \fB\fBblock\fR\fR
 357 .ad
 358 .RS 11n
 359 Treats the input as a sequence of \fBNEWLINE\fR-terminated or
 360 \fBEOF\fR-terminated variable-length records independent of the input block
 361 boundaries. Each record is converted to a record with a fixed length specified
 362 by the conversion block size. Any \fBNEWLINE\fR character is removed from the
 363 input line. \fBSPACE\fR characters are appended to lines that are shorter than
 364 their conversion block size to fill the block. Lines that are longer than the
 365 conversion block size are truncated to the largest number of characters that
 366 will fit into that size. The number of truncated lines is reported.
 367 .RE
 368 
 369 .sp
 370 .ne 2
 371 .na
 372 \fB\fBunblock\fR\fR
 373 .ad
 374 .RS 11n
 375 Converts fixed-length records to variable length. Reads a number of bytes equal
 376 to the conversion block size (or the number of bytes remaining in the input, if
 377 less than the conversion block size), delete all trailing \fBSPACE\fR
 378 characters, and append a \fBNEWLINE\fR character.
 379 .RE
 380 
 381 The  \fBblock\fR and \fBunblock\fR values are mutually exclusive.
 382 .sp
 383 .ne 2
 384 .na
 385 \fB\fBlcase\fR\fR
 386 .ad
 387 .RS 9n
 388 Maps upper-case characters specified by the \fBLC_CTYPE\fR keyword
 389 \fBtolower\fR to the corresponding lower-case character. Characters for which
 390 no mapping is specified are not modified by this conversion.
 391 .RE
 392 
 393 .sp
 394 .ne 2
 395 .na
 396 \fB\fBucase\fR\fR
 397 .ad
 398 .RS 9n
 399 Maps lower-case characters specified by the \fBLC_CTYPE\fR keyword
 400 \fBtoupper\fR to the corresponding upper-case character. Characters for which
 401 no mapping is specified are not modified by this conversion.
 402 .RE
 403 
 404 The \fBlcase\fR and \fBucase\fR symbols are mutually exclusive.
 405 .sp
 406 .ne 2
 407 .na
 408 \fB\fBswab\fR\fR
 409 .ad
 410 .RS 11n
 411 Swaps every pair of input bytes. If the current input record is an odd number
 412 of bytes, the last byte in the input record is ignored.
 413 .RE
 414 
 415 .sp
 416 .ne 2
 417 .na
 418 \fB\fBnoerror\fR\fR
 419 .ad
 420 .RS 11n
 421 Does not stop processing on an input error. When an input error occurs, a
 422 diagnostic message is written on standard error, followed by the current input
 423 and output block counts in the same format as used at completion. If the
 424 \fBsync\fR conversion is specified, the missing input is replaced with null
 425 bytes and processed normally. Otherwise, the input block will be omitted from
 426 the output.
 427 .RE
 428 
 429 .sp
 430 .ne 2
 431 .na
 432 \fB\fBnotrunc\fR\fR
 433 .ad
 434 .RS 11n
 435 Does not truncate the output file. Preserves blocks in the output file not
 436 explicitly written by this invocation of \fBdd\fR. (See also the preceding
 437 \fBof=\fR\fIfile\fR operand.)
 438 .RE
 439 
 440 .sp
 441 .ne 2
 442 .na
 443 \fB\fBsync\fR\fR
 444 .ad
 445 .RS 11n
 446 Pads every input block to the size of the \fBibs=\fR buffer, appending null
 447 bytes. (If either \fBblock\fR or \fBunblock\fR is also specified, appends
 448 \fBSPACE\fR characters, rather than null bytes.)
 449 .RE
 450 
 451 .RE
 452 
 453 .sp
 454 .ne 2
 455 .na
 456 \fB\fBoflag=\fR\fIvalue\fR[\fB,\fR\fIvalue\fR.\|.\|.\|]\fR
 457 .ad
 458 .sp .6
 459 Where \fIvalue\fRs are comma-separated symbols from the following list which
 460 affect the behavior of writing the output file:
 461 .sp
 462 .ne 2
 463 .na
 464 \fB\fBdsync\fR\fR
 465 .ad
 466 .RS 11n
 467 The output file is opened with the \fBO_DSYNC\fR flag set. All data writes will
 468 be synchronous. For more information on \fBO_DSYNC\fR see \fBfcntl.h\fR(3HEAD).
 469 .RE
 470 
 471 .sp
 472 .ne 2
 473 .na
 474 \fB\fBsync\fR\fR
 475 .ad
 476 .RS 11n
 477 The output file is opened with the \fBO_SYNC\fR flag set. All data and metadata
 478 writes will be synchronous. For more information on \fBO_SYNC\fR see
 479 \fBfcntl.h\fR(3HEAD).
 480 .RE
 481 
 482 .sp
 483 .LP
 484 If operands other than \fBconv=\fR and \fBoflag=\fR are specified more than once,
 485 the last specified \fBoperand=\fR\fIvalue\fR is used.
 486 .sp
 487 .LP
 488 For the \fBbs=\fR, \fBcbs=\fR, \fBibs=\fR, and \fBobs=\fR operands, the
 489 application must supply an expression specifying a size in bytes. The
 490 expression, \fBexpr\fR, can be:
 491 .RS +4
 492 .TP
 493 1.
 494 a positive decimal number
 495 .RE
 496 .RS +4
 497 .TP
 498 2.
 499 a positive decimal number followed by \fBk\fR, specifying multiplication by
 500 1024
 501 .RE
 502 .RS +4
 503 .TP
 504 3.
 505 a positive decimal number followed by \fBM\fR, specifying multiplication by
 506 1024*1024
 507 .RE
 508 .RS +4
 509 .TP
 510 4.
 511 a positive decimal number followed by \fBG\fR, specifying multiplication by
 512 1024*1024*1024
 513 .RE
 514 .RS +4
 515 .TP
 516 5.
 517 a positive decimal number followed by \fBT\fR, specifying multiplication by
 518 1024*1024*1024*1024
 519 .RE
 520 .RS +4
 521 .TP
 522 6.
 523 a positive decimal number followed by \fBP\fR, specifying multiplication by
 524 1024*1024*1024*1024*1024
 525 .RE
 526 .RS +4
 527 .TP
 528 7.
 529 a positive decimal number followed by \fBE\fR, specifying multiplication by
 530 1024*1024*1024*1024*1024*1024
 531 .RE
 532 .RS +4
 533 .TP
 534 8.
 535 a positive decimal number followed by \fBZ\fR, specifying multiplication by
 536 1024*1024*1024*1024*1024*1024*1024
 537 .RE
 538 .RS +4
 539 .TP
 540 9.
 541 a positive decimal number followed by \fBb\fR, specifying multiplication by
 542 512
 543 .RE
 544 .RS +4
 545 .TP
 546 10.
 547 two or more positive decimal numbers (with or without \fBk\fR or \fBb\fR)
 548 separated by \fBx\fR, specifying the product of the indicated values.
 549 .RE
 550 .sp
 551 .LP
 552 All of the operands will be processed before any input is read.
 553 .SH SIGNALS
 554 .LP
 555 When \fBdd\fR receives either SIGINFO or SIGUSR1, \fBdd\fR will emit the current
 556 input and output block counts, total bytes written, total time elapsed, and the
 557 number of bytes per second to standard error. This is the same information
 558 format that \fBdd\fR emits when it successfully completes. Users may send
 559 SIGINFO via their terminal. The default character is ^T, see \fBstty\fR(1) for
 560 more information.
 561 .sp
 562 .LP
 563 For \fBSIGINT\fR, \fBdd\fR writes status information to standard error before
 564 exiting. \fBdd\fR takes the standard action for all other signals.
 565 
 566 .SH USAGE
 567 .LP
 568 See \fBlargefile\fR(5) for the description of the behavior of \fBdd\fR when
 569 encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).
 570 .SH EXAMPLES
 571 .LP
 572 \fBExample 1 \fRCopying from one tape drive to another
 573 .sp
 574 .LP
 575 The following example copies from tape drive \fB0\fR to tape drive \fB1\fR,
 576 using a common historical device naming convention.
 577 
 578 .sp
 579 .in +2
 580 .nf
 581 example% \fBdd if=/dev/rmt/0h  of=/dev/rmt/1h\fR
 582 .fi
 583 .in -2
 584 .sp
 585 
 586 .LP
 587 \fBExample 2 \fRStripping the first 10 bytes from standard input
 588 .sp
 589 .LP
 590 The following example strips the first 10 bytes from standard input:
 591 
 592 .sp
 593 .in +2
 594 .nf
 595 example% \fBdd ibs=10  skip=1\fR
 596 .fi
 597 .in -2
 598 .sp
 599 
 600 .LP
 601 \fBExample 3 \fRReading a tape into an ASCII file
 602 .sp
 603 .LP
 604 This example reads an \fBEBCDIC\fR tape blocked ten 80-byte \fBEBCDIC\fR card
 605 images per block into the \fBASCII\fR file \fBx\fR:
 606 
 607 .sp
 608 .in +2
 609 .nf
 610 example% \fBdd if=/dev/tape of=x ibs=800 cbs=80 conv=ascii,lcase\fR
 611 .fi
 612 .in -2
 613 .sp
 614 
 615 .LP
 616 \fBExample 4 \fRUsing conv=sync to write to tape
 617 .sp
 618 .LP
 619 The following example uses \fBconv=sync\fR when writing to a tape:
 620 
 621 .sp
 622 .in +2
 623 .nf
 624 example% \fBtar cvf - . | compress | dd obs=1024k of=/dev/rmt/0 conv=sync\fR
 625 .fi
 626 .in -2
 627 .sp
 628 
 629 .SH ENVIRONMENT VARIABLES
 630 .LP
 631 See \fBenviron\fR(5) for descriptions of the following environment variables
 632 that affect the execution of \fBdd\fR: \fBLANG\fR, \fBLC_ALL\fR,
 633 \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
 634 .SH EXIT STATUS
 635 .LP
 636 The following exit values are returned:
 637 .sp
 638 .ne 2
 639 .na
 640 \fB\fB0\fR\fR
 641 .ad
 642 .RS 6n
 643 The input file was copied successfully.
 644 .RE
 645 
 646 .sp
 647 .ne 2
 648 .na
 649 \fB\fB>0\fR\fR
 650 .ad
 651 .RS 6n
 652 An error occurred.
 653 .RE
 654 
 655 .sp
 656 .LP
 657 If an input error is detected and the \fBnoerror\fR conversion has not been
 658 specified, any partial output block will be written to the output file, a
 659 diagnostic message will be written, and the copy operation will be
 660 discontinued. If some other error is detected, a diagnostic message will be
 661 written and the copy operation will be discontinued.
 662 .SH ATTRIBUTES
 663 .LP
 664 See \fBattributes\fR(5) for descriptions of the following attributes:
 665 .sp
 666 
 667 .sp
 668 .TS
 669 box;
 670 c | c
 671 l | l .
 672 ATTRIBUTE TYPE  ATTRIBUTE VALUE
 673 _
 674 Interface Stability     Standard
 675 .TE
 676 
 677 .SH SEE ALSO
 678 .LP
 679 \fBcp\fR(1), \fBsed\fR(1), \fBtr\fR(1), \fBfcntl.h\fR(3HEAD),
 680 \fBattributes\fR(5), \fBenviron\fR(5), \fBlargefile\fR(5), \fBstandards\fR(5)
 681 .SH DIAGNOSTICS
 682 .ne 2
 683 .na
 684 \fB\fBf+p records in(out)\fR\fR
 685 .ad
 686 .RS 23n
 687 numbers of full and partial blocks read(written)
 688 .RE
 689 
 690 .SH NOTES
 691 .LP
 692 Do not use \fBdd\fR to copy files between file systems having different block
 693 sizes.
 694 .sp
 695 .LP
 696 Using a  blocked device to copy a file will result in extra nulls being added
 697 to the file to pad the final block to the block boundary.
 698 .sp
 699 .LP
 700 When  \fBdd\fR reads from a pipe, using the  \fBibs=X\fR and  \fBobs=Y\fR
 701 operands, the output will always be blocked in chunks of size Y. When
 702 \fBbs=Z\fR is used, the output blocks will be whatever was available to be read
 703 from the pipe at the time.
 704 .sp
 705 .LP
 706 When using \fBdd\fR to copy files to a tape device, the file size must be a
 707 multiple of the device sector size (for example, 512 Kbyte).  To  copy files of
 708 arbitrary size to a tape device, use  \fBtar\fR(1) or  \fBcpio\fR(1).