1 .\"
   2 .\" Sun Microsystems, Inc. gratefully acknowledges The Open Group for
   3 .\" permission to reproduce portions of its copyrighted documentation.
   4 .\" Original documentation from The Open Group can be obtained online at
   5 .\" http://www.opengroup.org/bookstore/.
   6 .\"
   7 .\" The Institute of Electrical and Electronics Engineers and The Open
   8 .\" Group, have given us permission to reprint portions of their
   9 .\" documentation.
  10 .\"
  11 .\" In the following statement, the phrase ``this text'' refers to portions
  12 .\" of the system documentation.
  13 .\"
  14 .\" Portions of this text are reprinted and reproduced in electronic form
  15 .\" in the SunOS Reference Manual, from IEEE Std 1003.1, 2004 Edition,
  16 .\" Standard for Information Technology -- Portable Operating System
  17 .\" Interface (POSIX), The Open Group Base Specifications Issue 6,
  18 .\" Copyright (C) 2001-2004 by the Institute of Electrical and Electronics
  19 .\" Engineers, Inc and The Open Group.  In the event of any discrepancy
  20 .\" between these versions and the original IEEE and The Open Group
  21 .\" Standard, the original IEEE and The Open Group Standard is the referee
  22 .\" document.  The original Standard can be obtained online at
  23 .\" http://www.opengroup.org/unix/online.html.
  24 .\"
  25 .\" This notice shall appear on any product containing this material.
  26 .\"
  27 .\" The contents of this file are subject to the terms of the
  28 .\" Common Development and Distribution License (the "License").
  29 .\" You may not use this file except in compliance with the License.
  30 .\"
  31 .\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
  32 .\" or http://www.opensolaris.org/os/licensing.
  33 .\" See the License for the specific language governing permissions
  34 .\" and limitations under the License.
  35 .\"
  36 .\" When distributing Covered Code, include this CDDL HEADER in each
  37 .\" file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  38 .\" If applicable, add the following below this CDDL HEADER, with the
  39 .\" fields enclosed by brackets "[]" replaced with your own identifying
  40 .\" information: Portions Copyright [yyyy] [name of copyright owner]
  41 .\"
  42 .\"
  43 .\" Copyright 1989 AT&T
  44 .\" Copyright (c) 1992, X/Open Company Limited  All Rights Reserved
  45 .\" Portions Copyright (c) 1995, Sun Microsystems, Inc.  All Rights Reserved
  46 .\" Copyright (c) 2014, Joyent, Inc.  All rights Reserved.
  47 .\" Copyright (c) 2014 by Delphix. All rights reserved.
  48 .\"
  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 .sp
 452 .ne 2
 453 .na
 454 \fB\fBoflag=\fR\fIvalue\fR[\fB,\fR\fIvalue\fR.\|.\|.\|]\fR
 455 .ad
 456 .sp .6
 457 Where \fIvalue\fRs are comma-separated symbols from the following list which
 458 affect the behavior of writing the output file:
 459 .sp
 460 .ne 2
 461 .na
 462 \fB\fBdsync\fR\fR
 463 .ad
 464 .RS 11n
 465 The output file is opened with the \fBO_DSYNC\fR flag set. All data writes will
 466 be synchronous. For more information on \fBO_DSYNC\fR see \fBfcntl.h\fR(3HEAD).
 467 .RE
 468 
 469 .sp
 470 .ne 2
 471 .na
 472 \fB\fBsync\fR\fR
 473 .ad
 474 .RS 11n
 475 The output file is opened with the \fBO_SYNC\fR flag set. All data and metadata
 476 writes will be synchronous. For more information on \fBO_SYNC\fR see
 477 \fBfcntl.h\fR(3HEAD).
 478 .RE
 479 
 480 .sp
 481 .LP
 482 If operands other than \fBconv=\fR and \fBoflag=\fR are specified more than once,
 483 the last specified \fBoperand=\fR\fIvalue\fR is used.
 484 .sp
 485 .LP
 486 For the \fBbs=\fR, \fBcbs=\fR, \fBibs=\fR, and \fBobs=\fR operands, the
 487 application must supply an expression specifying a size in bytes. The
 488 expression, \fBexpr\fR, can be:
 489 .RS +4
 490 .TP
 491 1.
 492 a positive decimal number
 493 .RE
 494 .RS +4
 495 .TP
 496 2.
 497 a positive decimal number followed by \fBk\fR, specifying multiplication by
 498 1024
 499 .RE
 500 .RS +4
 501 .TP
 502 3.
 503 a positive decimal number followed by \fBM\fR, specifying multiplication by
 504 1024*1024
 505 .RE
 506 .RS +4
 507 .TP
 508 4.
 509 a positive decimal number followed by \fBG\fR, specifying multiplication by
 510 1024*1024*1024
 511 .RE
 512 .RS +4
 513 .TP
 514 5.
 515 a positive decimal number followed by \fBT\fR, specifying multiplication by
 516 1024*1024*1024*1024
 517 .RE
 518 .RS +4
 519 .TP
 520 6.
 521 a positive decimal number followed by \fBP\fR, specifying multiplication by
 522 1024*1024*1024*1024*1024
 523 .RE
 524 .RS +4
 525 .TP
 526 7.
 527 a positive decimal number followed by \fBE\fR, specifying multiplication by
 528 1024*1024*1024*1024*1024*1024
 529 .RE
 530 .RS +4
 531 .TP
 532 8.
 533 a positive decimal number followed by \fBZ\fR, specifying multiplication by
 534 1024*1024*1024*1024*1024*1024*1024
 535 .RE
 536 .RS +4
 537 .TP
 538 9.
 539 a positive decimal number followed by \fBb\fR, specifying multiplication by
 540 512
 541 .RE
 542 .RS +4
 543 .TP
 544 10.
 545 two or more positive decimal numbers (with or without \fBk\fR or \fBb\fR)
 546 separated by \fBx\fR, specifying the product of the indicated values.
 547 .RE
 548 .sp
 549 .LP
 550 All of the operands will be processed before any input is read.
 551 .SH SIGNALS
 552 .LP
 553 When \fBdd\fR receives either SIGINFO or SIGUSR1, \fBdd\fR will emit the current
 554 input and output block counts, total bytes written, total time elapsed, and the
 555 number of bytes per second to standard error. This is the same information
 556 format that \fBdd\fR emits when it successfully completes. Users may send
 557 SIGINFO via their terminal. The default character is ^T, see \fBstty\fR(1) for
 558 more information.
 559 .sp
 560 .LP
 561 For \fBSIGINT\fR, \fBdd\fR writes status information to standard error before
 562 exiting. \fBdd\fR takes the standard action for all other signals.
 563 
 564 .SH USAGE
 565 .LP
 566 See \fBlargefile\fR(5) for the description of the behavior of \fBdd\fR when
 567 encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).
 568 .SH EXAMPLES
 569 .LP
 570 \fBExample 1 \fRCopying from one tape drive to another
 571 .sp
 572 .LP
 573 The following example copies from tape drive \fB0\fR to tape drive \fB1\fR,
 574 using a common historical device naming convention.
 575 
 576 .sp
 577 .in +2
 578 .nf
 579 example% \fBdd if=/dev/rmt/0h  of=/dev/rmt/1h\fR
 580 .fi
 581 .in -2
 582 .sp
 583 
 584 .LP
 585 \fBExample 2 \fRStripping the first 10 bytes from standard input
 586 .sp
 587 .LP
 588 The following example strips the first 10 bytes from standard input:
 589 
 590 .sp
 591 .in +2
 592 .nf
 593 example% \fBdd ibs=10  skip=1\fR
 594 .fi
 595 .in -2
 596 .sp
 597 
 598 .LP
 599 \fBExample 3 \fRReading a tape into an ASCII file
 600 .sp
 601 .LP
 602 This example reads an \fBEBCDIC\fR tape blocked ten 80-byte \fBEBCDIC\fR card
 603 images per block into the \fBASCII\fR file \fBx\fR:
 604 
 605 .sp
 606 .in +2
 607 .nf
 608 example% \fBdd if=/dev/tape of=x ibs=800 cbs=80 conv=ascii,lcase\fR
 609 .fi
 610 .in -2
 611 .sp
 612 
 613 .LP
 614 \fBExample 4 \fRUsing conv=sync to write to tape
 615 .sp
 616 .LP
 617 The following example uses \fBconv=sync\fR when writing to a tape:
 618 
 619 .sp
 620 .in +2
 621 .nf
 622 example% \fBtar cvf - . | compress | dd obs=1024k of=/dev/rmt/0 conv=sync\fR
 623 .fi
 624 .in -2
 625 .sp
 626 
 627 .SH ENVIRONMENT VARIABLES
 628 .LP
 629 See \fBenviron\fR(5) for descriptions of the following environment variables
 630 that affect the execution of \fBdd\fR: \fBLANG\fR, \fBLC_ALL\fR,
 631 \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
 632 .SH EXIT STATUS
 633 .LP
 634 The following exit values are returned:
 635 .sp
 636 .ne 2
 637 .na
 638 \fB\fB0\fR\fR
 639 .ad
 640 .RS 6n
 641 The input file was copied successfully.
 642 .RE
 643 
 644 .sp
 645 .ne 2
 646 .na
 647 \fB\fB>0\fR\fR
 648 .ad
 649 .RS 6n
 650 An error occurred.
 651 .RE
 652 
 653 .sp
 654 .LP
 655 If an input error is detected and the \fBnoerror\fR conversion has not been
 656 specified, any partial output block will be written to the output file, a
 657 diagnostic message will be written, and the copy operation will be
 658 discontinued. If some other error is detected, a diagnostic message will be
 659 written and the copy operation will be discontinued.
 660 .SH ATTRIBUTES
 661 .LP
 662 See \fBattributes\fR(5) for descriptions of the following attributes:
 663 .sp
 664 
 665 .sp
 666 .TS
 667 box;
 668 c | c
 669 l | l .
 670 ATTRIBUTE TYPE  ATTRIBUTE VALUE
 671 _
 672 Interface Stability     Standard
 673 .TE
 674 
 675 .SH SEE ALSO
 676 .LP
 677 \fBcp\fR(1), \fBsed\fR(1), \fBtr\fR(1), \fBfcntl.h\fR(3HEAD),
 678 \fBattributes\fR(5), \fBenviron\fR(5), \fBlargefile\fR(5), \fBstandards\fR(5)
 679 .SH DIAGNOSTICS
 680 .ne 2
 681 .na
 682 \fB\fBf+p records in(out)\fR\fR
 683 .ad
 684 .RS 23n
 685 numbers of full and partial blocks read(written)
 686 .RE
 687 
 688 .SH NOTES
 689 .LP
 690 Do not use \fBdd\fR to copy files between file systems having different block
 691 sizes.
 692 .sp
 693 .LP
 694 Using a  blocked device to copy a file will result in extra nulls being added
 695 to the file to pad the final block to the block boundary.
 696 .sp
 697 .LP
 698 When  \fBdd\fR reads from a pipe, using the  \fBibs=X\fR and  \fBobs=Y\fR
 699 operands, the output will always be blocked in chunks of size Y. When
 700 \fBbs=Z\fR is used, the output blocks will be whatever was available to be read
 701 from the pipe at the time.
 702 .sp
 703 .LP
 704 When using \fBdd\fR to copy files to a tape device, the file size must be a
 705 multiple of the device sector size (for example, 512 Kbyte).  To  copy files of
 706 arbitrary size to a tape device, use  \fBtar\fR(1) or  \fBcpio\fR(1).