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 October 5, 2016 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 ".Cm of Ns = Ns Ar 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 iseek Ns = Ns Ar n 106Seek on the input file 107.Ar n 108blocks. 109This is synonymous with 110.Cm skip Ns = Ns Ar n . 111.It Cm obs Ns = Ns Ar n 112Set the output block size to 113.Ar n 114bytes instead of the default 512. 115.It Cm of Ns = Ns Ar file 116Write output to 117.Ar file 118instead of the standard output. 119Any regular output file is truncated unless the 120.Cm notrunc 121conversion value is specified. 122If an initial portion of the output file is seeked past (see the 123.Cm oseek 124operand), 125the output file is truncated at that point. 126.It Cm oseek Ns = Ns Ar n 127Seek on the output file 128.Ar n 129blocks. 130This is synonymous with 131.Cm seek Ns = Ns Ar n . 132.It Cm seek Ns = Ns Ar n 133Seek 134.Ar n 135blocks from the beginning of the output before copying. 136On non-tape devices, an 137.Xr lseek 2 138operation is used. 139Otherwise, existing blocks are read and the data discarded. 140If the user does not have read permission for the tape, it is positioned 141using the tape 142.Xr ioctl 2 143function calls. 144If the seek operation is past the end of file, space from the current 145end of file to the specified offset is filled with blocks of 146.Dv NUL 147bytes. 148.It Cm skip Ns = Ns Ar n 149Skip 150.Ar n 151blocks from the beginning of the input before copying. 152On input which supports seeks, an 153.Xr lseek 2 154operation is used. 155Otherwise, input data is read and discarded. 156For pipes, the correct number of bytes is read. 157For all other devices, the correct number of blocks is read without 158distinguishing between a partial or complete block being read. 159.It Cm speed Ns = Ns Ar n 160Limit the copying speed to 161.Ar n 162bytes per second. 163.It Cm status Ns = Ns Ar value 164Where 165.Cm value 166is one of the symbols from the following list. 167.Bl -tag -width ".Cm noxfer" 168.It Cm noxfer 169Do not print the transfer statistics as the last line of status output. 170.It Cm none 171Do not print the status output. 172Error messages are shown; informational messages are not. 173.El 174.It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ... 175Where 176.Cm value 177is one of the symbols from the following list. 178.Bl -tag -width ".Cm unblock" 179.It Cm ascii , oldascii 180The same as the 181.Cm unblock 182value except that characters are translated from 183.Tn EBCDIC 184to 185.Tn ASCII 186before the 187records are converted. 188(These values imply 189.Cm unblock 190if the operand 191.Cm cbs 192is also specified.) 193There are two conversion maps for 194.Tn ASCII . 195The value 196.Cm ascii 197specifies the recommended one which is compatible with 198.At V . 199The value 200.Cm oldascii 201specifies the one used in historic 202.At 203and 204.No pre- Ns Bx 4.3 reno 205systems. 206.It Cm block 207Treats the input as a sequence of newline or end-of-file terminated variable 208length records independent of input and output block boundaries. 209Any trailing newline character is discarded. 210Each input record is converted to a fixed length output record where the 211length is specified by the 212.Cm cbs 213operand. 214Input records shorter than the conversion record size are padded with spaces. 215Input records longer than the conversion record size are truncated. 216The number of truncated input records, if any, are reported to the standard 217error output at the completion of the copy. 218.It Cm ebcdic , ibm , oldebcdic , oldibm 219The same as the 220.Cm block 221value except that characters are translated from 222.Tn ASCII 223to 224.Tn EBCDIC 225after the 226records are converted. 227(These values imply 228.Cm block 229if the operand 230.Cm cbs 231is also specified.) 232There are four conversion maps for 233.Tn EBCDIC . 234The value 235.Cm ebcdic 236specifies the recommended one which is compatible with 237.At V . 238The value 239.Cm ibm 240is a slightly different mapping, which is compatible with the 241.At V 242.Cm ibm 243value. 244The values 245.Cm oldebcdic 246and 247.Cm oldibm 248are maps used in historic 249.At 250and 251.No pre- Ns Bx 4.3 reno 252systems. 253.It Cm lcase 254Transform uppercase characters into lowercase characters. 255.It Cm pareven , parnone , parodd , parset 256Output data with the specified parity. 257The parity bit on input is stripped unless 258.Tn EBCDIC 259to 260.Tn ASCII 261conversions is also specified. 262.It Cm noerror 263Do not stop processing on an input error. 264When an input error occurs, a diagnostic message followed by the current 265input and output block counts will be written to the standard error output 266in the same format as the standard completion message. 267If the 268.Cm sync 269conversion is also specified, any missing input data will be replaced 270with 271.Dv NUL 272bytes (or with spaces if a block oriented conversion value was 273specified) and processed as a normal input buffer. 274If the 275.Cm fillchar 276option is specified, the fill character provided on the command line 277will override 278the automatic selection of the fill character. 279If the 280.Cm sync 281conversion is not specified, the input block is omitted from the output. 282On input files which are not tapes or pipes, the file offset 283will be positioned past the block in which the error occurred using 284.Xr lseek 2 . 285.It Cm notrunc 286Do not truncate the output file. 287This will preserve any blocks in the output file not explicitly written 288by 289.Nm . 290The 291.Cm notrunc 292value is not supported for tapes. 293.It Cm osync 294Pad the final output block to the full output block size. 295If the input file is not a multiple of the output block size 296after conversion, this conversion forces the final output block 297to be the same size as preceding blocks for use on devices that require 298regularly sized blocks to be written. 299This option is incompatible with use of the 300.Cm bs Ns = Ns Ar n 301block size specification. 302.It Cm sparse 303If one or more output blocks would consist solely of 304.Dv NUL 305bytes, try to seek the output file by the required space instead of 306filling them with 307.Dv NUL Ns s , 308resulting in a sparse file. 309.It Cm swab 310Swap every pair of input bytes. 311If an input buffer has an odd number of bytes, the last byte will be 312ignored during swapping. 313.It Cm sync 314Pad every input block to the input buffer size. 315Spaces are used for pad bytes if a block oriented conversion value is 316specified, otherwise 317.Dv NUL 318bytes are used. 319.It Cm ucase 320Transform lowercase characters into uppercase characters. 321.It Cm unblock 322Treats the input as a sequence of fixed length records independent of input 323and output block boundaries. 324The length of the input records is specified by the 325.Cm cbs 326operand. 327Any trailing space characters are discarded and a newline character is 328appended. 329.El 330.El 331.Pp 332Where sizes or speed are specified, a decimal, octal, or hexadecimal number of 333bytes is expected. 334If the number ends with a 335.Dq Li b , 336.Dq Li k , 337.Dq Li m , 338.Dq Li g , 339.Dq Li t , 340.Dq Li p , 341or 342.Dq Li w , 343the 344number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G), 3451099511627776 (1T), 1125899906842624 (1P) 346or the number of bytes in an integer, respectively. 347Two or more numbers may be separated by an 348.Dq Li x 349to indicate a product. 350.Pp 351When finished, 352.Nm 353displays the number of complete and partial input and output blocks, 354truncated input records and odd-length byte-swapping blocks to the 355standard error output. 356A partial input block is one where less than the input block size 357was read. 358A partial output block is one where less than the output block size 359was written. 360Partial output blocks to tape devices are considered fatal errors. 361Otherwise, the rest of the block will be written. 362Partial output blocks to character devices will produce a warning message. 363A truncated input block is one where a variable length record oriented 364conversion value was specified and the input line was too long to 365fit in the conversion record or was not newline terminated. 366.Pp 367Normally, data resulting from input or conversion or both are aggregated 368into output blocks of the specified size. 369After the end of input is reached, any remaining output is written as 370a block. 371This means that the final output block may be shorter than the output 372block size. 373.Pp 374If 375.Nm 376receives a 377.Dv SIGINFO 378(see the 379.Cm status 380argument for 381.Xr stty 1 ) 382signal, the current input and output block counts will 383be written to the standard error output 384in the same format as the standard completion message. 385If 386.Nm 387receives a 388.Dv SIGINT 389signal, the current input and output block counts will 390be written to the standard error output 391in the same format as the standard completion message and 392.Nm 393will exit. 394.Sh EXIT STATUS 395.Ex -std 396.Sh EXAMPLES 397Check that a disk drive contains no bad blocks: 398.Pp 399.Dl "dd if=/dev/ada0 of=/dev/null bs=1m" 400.Pp 401Do a refresh of a disk drive, in order to prevent presently 402recoverable read errors from progressing into unrecoverable read errors: 403.Pp 404.Dl "dd if=/dev/ada0 of=/dev/ada0 bs=1m" 405.Pp 406Remove parity bit from a file: 407.Pp 408.Dl "dd if=file conv=parnone of=file.txt" 409.Pp 410Check for (even) parity errors on a file: 411.Pp 412.Dl "dd if=file conv=pareven | cmp -x - file" 413.Pp 414To create an image of a Mode-1 CD-ROM, which is a commonly used format 415for data CD-ROM disks, use a block size of 2048 bytes: 416.Pp 417.Dl "dd if=/dev/cd0 of=filename.iso bs=2048" 418.Pp 419Write a filesystem image to a memory stick, padding the end with zeros, 420if necessary, to a 1MiB boundary: 421.Pp 422.Dl "dd if=memstick.img of=/dev/da0 bs=1m conv=noerror,sync" 423.Sh SEE ALSO 424.Xr cp 1 , 425.Xr mt 1 , 426.Xr recoverdisk 1 , 427.Xr tr 1 , 428.Xr geom 4 429.Sh STANDARDS 430The 431.Nm 432utility is expected to be a superset of the 433.St -p1003.2 434standard. 435The 436.Cm files 437and 438.Cm status 439operands and the 440.Cm ascii , 441.Cm ebcdic , 442.Cm ibm , 443.Cm oldascii , 444.Cm oldebcdic 445and 446.Cm oldibm 447values are extensions to the 448.Tn POSIX 449standard. 450.Sh HISTORY 451A 452.Nm 453command appeared in 454.At v5 . 455.Sh BUGS 456Protection mechanisms in the 457.Xr geom 4 458subsystem might prevent the super-user from writing blocks to a disk. 459Instructions for temporarily disabling these protection mechanisms can be 460found in the 461.Xr geom 4 462manpage. 463