1.\"- 2.\" Copyright (c) 1990, 1993 3.\" The Regents of the University of California. All rights reserved. 4.\" 5.\" This code is derived from software contributed to Berkeley by 6.\" Keith Muller of the University of California, San Diego. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)dd.1 8.2 (Berkeley) 1/13/94 33.\" $FreeBSD$ 34.\" 35.Dd March 26, 2019 36.Dt DD 1 37.Os 38.Sh NAME 39.Nm dd 40.Nd convert and copy a file 41.Sh SYNOPSIS 42.Nm 43.Op Ar operands ... 44.Sh DESCRIPTION 45The 46.Nm 47utility copies the standard input to the standard output. 48Input data is read and written in 512-byte blocks. 49If input reads are short, input from multiple reads are aggregated 50to form the output block. 51When finished, 52.Nm 53displays the number of complete and partial input and output blocks 54and truncated input records to the standard error output. 55.Pp 56The following operands are available: 57.Bl -tag -width "of=file" 58.It Cm bs Ns = Ns Ar n 59Set both input and output block size to 60.Ar n 61bytes, superseding the 62.Cm ibs 63and 64.Cm obs 65operands. 66If no conversion values other than 67.Cm noerror , 68.Cm notrunc 69or 70.Cm sync 71are specified, then each input block is copied to the output as a 72single block without any aggregation of short blocks. 73.It Cm cbs Ns = Ns Ar n 74Set the conversion record size to 75.Ar n 76bytes. 77The conversion record size is required by the record oriented conversion 78values. 79.It Cm count Ns = Ns Ar n 80Copy only 81.Ar n 82input blocks. 83.It Cm files Ns = Ns Ar n 84Copy 85.Ar n 86input files before terminating. 87This operand is only applicable when the input device is a tape. 88.It Cm fillchar Ns = Ns Ar c 89When padding a block in conversion mode or due to use of 90.Cm noerror 91and 92.Cm sync 93modes, fill with the specified 94.Tn ASCII 95character, rather than using a space or 96.Dv NUL . 97.It Cm ibs Ns = Ns Ar n 98Set the input block size to 99.Ar n 100bytes instead of the default 512. 101.It Cm if Ns = Ns Ar file 102Read input from 103.Ar file 104instead of the standard input. 105.It Cm iflag Ns = Ns Ar value Ns Op , Ns Ar value ... 106Where 107.Cm value 108is one of the symbols from the following list. 109.Bl -tag -width "fullblock" 110.It Cm fullblock 111Reading from the input file may not obtain a full block. 112When a read returns short, continue reading to fill the block. 113Without this flag, 114.Cm count 115limits the number of times 116.Xr read 2 117is called on the input rather than the number of blocks copied in full. 118May not be combined with 119.Cm conv=sync . 120.El 121.It Cm iseek Ns = Ns Ar n 122Seek on the input file 123.Ar n 124blocks. 125This is synonymous with 126.Cm skip Ns = Ns Ar n . 127.It Cm obs Ns = Ns Ar n 128Set the output block size to 129.Ar n 130bytes instead of the default 512. 131.It Cm of Ns = Ns Ar file 132Write output to 133.Ar file 134instead of the standard output. 135Any regular output file is truncated unless the 136.Cm notrunc 137conversion value is specified. 138If an initial portion of the output file is seeked past (see the 139.Cm oseek 140operand), 141the output file is truncated at that point. 142.It Cm oflag Ns = Ns Ar value Ns Op , Ns Ar value ... 143Where 144.Cm value 145is one of the symbols from the following list. 146.Bl -tag -width "fsync" 147.It Cm fsync 148Set the O_FSYNC flag on the output file to make writes synchronous. 149.It Cm sync 150Set the O_SYNC flag on the output file to make writes synchronous. 151This is synonymous with the 152.Cm fsync 153value. 154.El 155.It Cm oseek Ns = Ns Ar n 156Seek on the output file 157.Ar n 158blocks. 159This is synonymous with 160.Cm seek Ns = Ns Ar n . 161.It Cm seek Ns = Ns Ar n 162Seek 163.Ar n 164blocks from the beginning of the output before copying. 165On non-tape devices, an 166.Xr lseek 2 167operation is used. 168Otherwise, existing blocks are read and the data discarded. 169If the user does not have read permission for the tape, it is positioned 170using the tape 171.Xr ioctl 2 172function calls. 173If the seek operation is past the end of file, space from the current 174end of file to the specified offset is filled with blocks of 175.Dv NUL 176bytes. 177.It Cm skip Ns = Ns Ar n 178Skip 179.Ar n 180blocks from the beginning of the input before copying. 181On input which supports seeks, an 182.Xr lseek 2 183operation is used. 184Otherwise, input data is read and discarded. 185For pipes, the correct number of bytes is read. 186For all other devices, the correct number of blocks is read without 187distinguishing between a partial or complete block being read. 188.It Cm speed Ns = Ns Ar n 189Limit the copying speed to 190.Ar n 191bytes per second. 192.It Cm status Ns = Ns Ar value 193Where 194.Cm value 195is one of the symbols from the following list. 196.Bl -tag -width "progress" 197.It Cm noxfer 198Do not print the transfer statistics as the last line of status output. 199.It Cm none 200Do not print the status output. 201Error messages are shown; informational messages are not. 202.It Cm progress 203Print basic transfer statistics once per second. 204.El 205.It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ... 206Where 207.Cm value 208is one of the symbols from the following list. 209.Bl -tag -width "unblock" 210.It Cm ascii , oldascii 211The same as the 212.Cm unblock 213value except that characters are translated from 214.Tn EBCDIC 215to 216.Tn ASCII 217before the 218records are converted. 219(These values imply 220.Cm unblock 221if the operand 222.Cm cbs 223is also specified.) 224There are two conversion maps for 225.Tn ASCII . 226The value 227.Cm ascii 228specifies the recommended one which is compatible with 229.At V . 230The value 231.Cm oldascii 232specifies the one used in historic 233.At 234and 235.No pre- Ns Bx 4.3 reno 236systems. 237.It Cm block 238Treats the input as a sequence of newline or end-of-file terminated variable 239length records independent of input and output block boundaries. 240Any trailing newline character is discarded. 241Each input record is converted to a fixed length output record where the 242length is specified by the 243.Cm cbs 244operand. 245Input records shorter than the conversion record size are padded with spaces. 246Input records longer than the conversion record size are truncated. 247The number of truncated input records, if any, are reported to the standard 248error output at the completion of the copy. 249.It Cm ebcdic , ibm , oldebcdic , oldibm 250The same as the 251.Cm block 252value except that characters are translated from 253.Tn ASCII 254to 255.Tn EBCDIC 256after the 257records are converted. 258(These values imply 259.Cm block 260if the operand 261.Cm cbs 262is also specified.) 263There are four conversion maps for 264.Tn EBCDIC . 265The value 266.Cm ebcdic 267specifies the recommended one which is compatible with 268.At V . 269The value 270.Cm ibm 271is a slightly different mapping, which is compatible with the 272.At V 273.Cm ibm 274value. 275The values 276.Cm oldebcdic 277and 278.Cm oldibm 279are maps used in historic 280.At 281and 282.No pre- Ns Bx 4.3 reno 283systems. 284.It Cm fdatasync 285Perform an 286.Xr fdatasync 2 287on the output file before closing it. 288.It Cm fsync 289Perform an 290.Xr fsync 2 291on the output file before closing it. 292.It Cm lcase 293Transform uppercase characters into lowercase characters. 294.It Cm pareven , parnone , parodd , parset 295Output data with the specified parity. 296The parity bit on input is stripped unless 297.Tn EBCDIC 298to 299.Tn ASCII 300conversions is also specified. 301.It Cm noerror 302Do not stop processing on an input error. 303When an input error occurs, a diagnostic message followed by the current 304input and output block counts will be written to the standard error output 305in the same format as the standard completion message. 306If the 307.Cm sync 308conversion is also specified, any missing input data will be replaced 309with 310.Dv NUL 311bytes (or with spaces if a block oriented conversion value was 312specified) and processed as a normal input buffer. 313If the 314.Cm fillchar 315option is specified, the fill character provided on the command line 316will override 317the automatic selection of the fill character. 318If the 319.Cm sync 320conversion is not specified, the input block is omitted from the output. 321On input files which are not tapes or pipes, the file offset 322will be positioned past the block in which the error occurred using 323.Xr lseek 2 . 324.It Cm notrunc 325Do not truncate the output file. 326This will preserve any blocks in the output file not explicitly written 327by 328.Nm . 329The 330.Cm notrunc 331value is not supported for tapes. 332.It Cm osync 333Pad the final output block to the full output block size. 334If the input file is not a multiple of the output block size 335after conversion, this conversion forces the final output block 336to be the same size as preceding blocks for use on devices that require 337regularly sized blocks to be written. 338This option is incompatible with use of the 339.Cm bs Ns = Ns Ar n 340block size specification. 341.It Cm sparse 342If one or more output blocks would consist solely of 343.Dv NUL 344bytes, try to seek the output file by the required space instead of 345filling them with 346.Dv NUL Ns s , 347resulting in a sparse file. 348.It Cm swab 349Swap every pair of input bytes. 350If an input buffer has an odd number of bytes, the last byte will be 351ignored during swapping. 352.It Cm sync 353Pad every input block to the input buffer size. 354Spaces are used for pad bytes if a block oriented conversion value is 355specified, otherwise 356.Dv NUL 357bytes are used. 358.It Cm ucase 359Transform lowercase characters into uppercase characters. 360.It Cm unblock 361Treats the input as a sequence of fixed length records independent of input 362and output block boundaries. 363The length of the input records is specified by the 364.Cm cbs 365operand. 366Any trailing space characters are discarded and a newline character is 367appended. 368.El 369.El 370.Pp 371Where sizes or speed are specified, a decimal, octal, or hexadecimal number of 372bytes is expected. 373If the number ends with a 374.Dq Li b , 375.Dq Li k , 376.Dq Li m , 377.Dq Li g , 378.Dq Li t , 379.Dq Li p , 380or 381.Dq Li w , 382the 383number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G), 3841099511627776 (1T), 1125899906842624 (1P) 385or the number of bytes in an integer, respectively. 386Two or more numbers may be separated by an 387.Dq Li x 388to indicate a product. 389.Pp 390When finished, 391.Nm 392displays the number of complete and partial input and output blocks, 393truncated input records and odd-length byte-swapping blocks to the 394standard error output. 395A partial input block is one where less than the input block size 396was read. 397A partial output block is one where less than the output block size 398was written. 399Partial output blocks to tape devices are considered fatal errors. 400Otherwise, the rest of the block will be written. 401Partial output blocks to character devices will produce a warning message. 402A truncated input block is one where a variable length record oriented 403conversion value was specified and the input line was too long to 404fit in the conversion record or was not newline terminated. 405.Pp 406Normally, data resulting from input or conversion or both are aggregated 407into output blocks of the specified size. 408After the end of input is reached, any remaining output is written as 409a block. 410This means that the final output block may be shorter than the output 411block size. 412.Pp 413If 414.Nm 415receives a 416.Dv SIGINFO 417(see the 418.Cm status 419argument for 420.Xr stty 1 ) 421signal, the current input and output block counts will 422be written to the standard error output 423in the same format as the standard completion message. 424If 425.Nm 426receives a 427.Dv SIGINT 428signal, the current input and output block counts will 429be written to the standard error output 430in the same format as the standard completion message and 431.Nm 432will exit. 433.Sh EXIT STATUS 434.Ex -std 435.Sh EXAMPLES 436Check that a disk drive contains no bad blocks: 437.Pp 438.Dl "dd if=/dev/ada0 of=/dev/null bs=1m" 439.Pp 440Do a refresh of a disk drive, in order to prevent presently 441recoverable read errors from progressing into unrecoverable read errors: 442.Pp 443.Dl "dd if=/dev/ada0 of=/dev/ada0 bs=1m" 444.Pp 445Remove parity bit from a file: 446.Pp 447.Dl "dd if=file conv=parnone of=file.txt" 448.Pp 449Check for (even) parity errors on a file: 450.Pp 451.Dl "dd if=file conv=pareven | cmp -x - file" 452.Pp 453To create an image of a Mode-1 CD-ROM, which is a commonly used format 454for data CD-ROM disks, use a block size of 2048 bytes: 455.Pp 456.Dl "dd if=/dev/cd0 of=filename.iso bs=2048" 457.Pp 458Write a filesystem image to a memory stick, padding the end with zeros, 459if necessary, to a 1MiB boundary: 460.Pp 461.Dl "dd if=memstick.img of=/dev/da0 bs=1m conv=noerror,sync" 462.Sh SEE ALSO 463.Xr cp 1 , 464.Xr mt 1 , 465.Xr recoverdisk 1 , 466.Xr tr 1 , 467.Xr geom 4 , 468.Xr trim 8 469.Sh STANDARDS 470The 471.Nm 472utility is expected to be a superset of the 473.St -p1003.2 474standard. 475The 476.Cm files 477and 478.Cm status 479operands and the 480.Cm ascii , 481.Cm ebcdic , 482.Cm ibm , 483.Cm oldascii , 484.Cm oldebcdic 485and 486.Cm oldibm 487values are extensions to the 488.Tn POSIX 489standard. 490.Sh HISTORY 491A 492.Nm 493command appeared in 494.At v5 . 495.Sh BUGS 496Protection mechanisms in the 497.Xr geom 4 498subsystem might prevent the super-user from writing blocks to a disk. 499Instructions for temporarily disabling these protection mechanisms can be 500found in the 501.Xr geom 4 502man page. 503