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 June 4, 2020 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.It Cm direct 121Set the O_DIRECT flag on the input file to make reads bypass any local caching. 122.El 123.It Cm iseek Ns = Ns Ar n 124Seek on the input file 125.Ar n 126blocks. 127This is synonymous with 128.Cm skip Ns = Ns Ar n . 129.It Cm obs Ns = Ns Ar n 130Set the output block size to 131.Ar n 132bytes instead of the default 512. 133.It Cm of Ns = Ns Ar file 134Write output to 135.Ar file 136instead of the standard output. 137Any regular output file is truncated unless the 138.Cm notrunc 139conversion value is specified. 140If an initial portion of the output file is seeked past (see the 141.Cm oseek 142operand), 143the output file is truncated at that point. 144.It Cm oflag Ns = Ns Ar value Ns Op , Ns Ar value ... 145Where 146.Cm value 147is one of the symbols from the following list. 148.Bl -tag -width "direct" 149.It Cm fsync 150Set the O_FSYNC flag on the output file to make writes synchronous. 151.It Cm sync 152Set the O_SYNC flag on the output file to make writes synchronous. 153This is synonymous with the 154.Cm fsync 155value. 156.It Cm direct 157Set the O_DIRECT flag on the output file to make writes bypass any local caching. 158.El 159.It Cm oseek Ns = Ns Ar n 160Seek on the output file 161.Ar n 162blocks. 163This is synonymous with 164.Cm seek Ns = Ns Ar n . 165.It Cm seek Ns = Ns Ar n 166Seek 167.Ar n 168blocks from the beginning of the output before copying. 169On non-tape devices, an 170.Xr lseek 2 171operation is used. 172Otherwise, existing blocks are read and the data discarded. 173If the user does not have read permission for the tape, it is positioned 174using the tape 175.Xr ioctl 2 176function calls. 177If the seek operation is past the end of file, space from the current 178end of file to the specified offset is filled with blocks of 179.Dv NUL 180bytes. 181.It Cm skip Ns = Ns Ar n 182Skip 183.Ar n 184blocks from the beginning of the input before copying. 185On input which supports seeks, an 186.Xr lseek 2 187operation is used. 188Otherwise, input data is read and discarded. 189For pipes, the correct number of bytes is read. 190For all other devices, the correct number of blocks is read without 191distinguishing between a partial or complete block being read. 192.It Cm speed Ns = Ns Ar n 193Limit the copying speed to 194.Ar n 195bytes per second. 196.It Cm status Ns = Ns Ar value 197Where 198.Cm value 199is one of the symbols from the following list. 200.Bl -tag -width "progress" 201.It Cm noxfer 202Do not print the transfer statistics as the last line of status output. 203.It Cm none 204Do not print the status output. 205Error messages are shown; informational messages are not. 206.It Cm progress 207Print basic transfer statistics once per second. 208.El 209.It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ... 210Where 211.Cm value 212is one of the symbols from the following list. 213.Bl -tag -width "unblock" 214.It Cm ascii , oldascii 215The same as the 216.Cm unblock 217value except that characters are translated from 218.Tn EBCDIC 219to 220.Tn ASCII 221before the 222records are converted. 223(These values imply 224.Cm unblock 225if the operand 226.Cm cbs 227is also specified.) 228There are two conversion maps for 229.Tn ASCII . 230The value 231.Cm ascii 232specifies the recommended one which is compatible with 233.At V . 234The value 235.Cm oldascii 236specifies the one used in historic 237.At 238and 239.No pre- Ns Bx 4.3 reno 240systems. 241.It Cm block 242Treats the input as a sequence of newline or end-of-file terminated variable 243length records independent of input and output block boundaries. 244Any trailing newline character is discarded. 245Each input record is converted to a fixed length output record where the 246length is specified by the 247.Cm cbs 248operand. 249Input records shorter than the conversion record size are padded with spaces. 250Input records longer than the conversion record size are truncated. 251The number of truncated input records, if any, are reported to the standard 252error output at the completion of the copy. 253.It Cm ebcdic , ibm , oldebcdic , oldibm 254The same as the 255.Cm block 256value except that characters are translated from 257.Tn ASCII 258to 259.Tn EBCDIC 260after the 261records are converted. 262(These values imply 263.Cm block 264if the operand 265.Cm cbs 266is also specified.) 267There are four conversion maps for 268.Tn EBCDIC . 269The value 270.Cm ebcdic 271specifies the recommended one which is compatible with 272.At V . 273The value 274.Cm ibm 275is a slightly different mapping, which is compatible with the 276.At V 277.Cm ibm 278value. 279The values 280.Cm oldebcdic 281and 282.Cm oldibm 283are maps used in historic 284.At 285and 286.No pre- Ns Bx 4.3 reno 287systems. 288.It Cm fdatasync 289Perform an 290.Xr fdatasync 2 291on the output file before closing it. 292.It Cm fsync 293Perform an 294.Xr fsync 2 295on the output file before closing it. 296.It Cm lcase 297Transform uppercase characters into lowercase characters. 298.It Cm pareven , parnone , parodd , parset 299Output data with the specified parity. 300The parity bit on input is stripped unless 301.Tn EBCDIC 302to 303.Tn ASCII 304conversions is also specified. 305.It Cm noerror 306Do not stop processing on an input error. 307When an input error occurs, a diagnostic message followed by the current 308input and output block counts will be written to the standard error output 309in the same format as the standard completion message. 310If the 311.Cm sync 312conversion is also specified, any missing input data will be replaced 313with 314.Dv NUL 315bytes (or with spaces if a block oriented conversion value was 316specified) and processed as a normal input buffer. 317If the 318.Cm fillchar 319option is specified, the fill character provided on the command line 320will override 321the automatic selection of the fill character. 322If the 323.Cm sync 324conversion is not specified, the input block is omitted from the output. 325On input files which are not tapes or pipes, the file offset 326will be positioned past the block in which the error occurred using 327.Xr lseek 2 . 328.It Cm notrunc 329Do not truncate the output file. 330This will preserve any blocks in the output file not explicitly written 331by 332.Nm . 333The 334.Cm notrunc 335value is not supported for tapes. 336.It Cm osync 337Pad the final output block to the full output block size. 338If the input file is not a multiple of the output block size 339after conversion, this conversion forces the final output block 340to be the same size as preceding blocks for use on devices that require 341regularly sized blocks to be written. 342This option is incompatible with use of the 343.Cm bs Ns = Ns Ar n 344block size specification. 345.It Cm sparse 346If one or more output blocks would consist solely of 347.Dv NUL 348bytes, try to seek the output file by the required space instead of 349filling them with 350.Dv NUL Ns s , 351resulting in a sparse file. 352.It Cm swab 353Swap every pair of input bytes. 354If an input buffer has an odd number of bytes, the last byte will be 355ignored during swapping. 356.It Cm sync 357Pad every input block to the input buffer size. 358Spaces are used for pad bytes if a block oriented conversion value is 359specified, otherwise 360.Dv NUL 361bytes are used. 362.It Cm ucase 363Transform lowercase characters into uppercase characters. 364.It Cm unblock 365Treats the input as a sequence of fixed length records independent of input 366and output block boundaries. 367The length of the input records is specified by the 368.Cm cbs 369operand. 370Any trailing space characters are discarded and a newline character is 371appended. 372.El 373.El 374.Pp 375Where sizes or speed are specified, a decimal, octal, or hexadecimal number of 376bytes is expected. 377If the number ends with a 378.Dq Li b , 379.Dq Li k , 380.Dq Li m , 381.Dq Li g , 382.Dq Li t , 383.Dq Li p , 384or 385.Dq Li w , 386the 387number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G), 3881099511627776 (1T), 1125899906842624 (1P) 389or the number of bytes in an integer, respectively. 390Two or more numbers may be separated by an 391.Dq Li x 392to indicate a product. 393.Pp 394When finished, 395.Nm 396displays the number of complete and partial input and output blocks, 397truncated input records and odd-length byte-swapping blocks to the 398standard error output. 399A partial input block is one where less than the input block size 400was read. 401A partial output block is one where less than the output block size 402was written. 403Partial output blocks to tape devices are considered fatal errors. 404Otherwise, the rest of the block will be written. 405Partial output blocks to character devices will produce a warning message. 406A truncated input block is one where a variable length record oriented 407conversion value was specified and the input line was too long to 408fit in the conversion record or was not newline terminated. 409.Pp 410Normally, data resulting from input or conversion or both are aggregated 411into output blocks of the specified size. 412After the end of input is reached, any remaining output is written as 413a block. 414This means that the final output block may be shorter than the output 415block size. 416.Pp 417If 418.Nm 419receives a 420.Dv SIGINFO 421(see the 422.Cm status 423argument for 424.Xr stty 1 ) 425signal, the current input and output block counts will 426be written to the standard error output 427in the same format as the standard completion message. 428If 429.Nm 430receives a 431.Dv SIGINT 432signal, the current input and output block counts will 433be written to the standard error output 434in the same format as the standard completion message and 435.Nm 436will exit. 437.Sh EXIT STATUS 438.Ex -std 439.Sh EXAMPLES 440Check that a disk drive contains no bad blocks: 441.Pp 442.Dl "dd if=/dev/ada0 of=/dev/null bs=1m" 443.Pp 444Do a refresh of a disk drive, in order to prevent presently 445recoverable read errors from progressing into unrecoverable read errors: 446.Pp 447.Dl "dd if=/dev/ada0 of=/dev/ada0 bs=1m" 448.Pp 449Remove parity bit from a file: 450.Pp 451.Dl "dd if=file conv=parnone of=file.txt" 452.Pp 453Check for (even) parity errors on a file: 454.Pp 455.Dl "dd if=file conv=pareven | cmp -x - file" 456.Pp 457To create an image of a Mode-1 CD-ROM, which is a commonly used format 458for data CD-ROM disks, use a block size of 2048 bytes: 459.Pp 460.Dl "dd if=/dev/cd0 of=filename.iso bs=2048" 461.Pp 462Write a filesystem image to a memory stick, padding the end with zeros, 463if necessary, to a 1MiB boundary: 464.Pp 465.Dl "dd if=memstick.img of=/dev/da0 bs=1m conv=noerror,sync" 466.Sh SEE ALSO 467.Xr cp 1 , 468.Xr mt 1 , 469.Xr recoverdisk 1 , 470.Xr tr 1 , 471.Xr geom 4 , 472.Xr trim 8 473.Sh STANDARDS 474The 475.Nm 476utility is expected to be a superset of the 477.St -p1003.2 478standard. 479The 480.Cm files 481and 482.Cm status 483operands and the 484.Cm ascii , 485.Cm ebcdic , 486.Cm ibm , 487.Cm oldascii , 488.Cm oldebcdic 489and 490.Cm oldibm 491values are extensions to the 492.Tn POSIX 493standard. 494.Sh HISTORY 495A 496.Nm 497command appeared in 498.At v5 . 499.Sh BUGS 500Protection mechanisms in the 501.Xr geom 4 502subsystem might prevent the super-user from writing blocks to a disk. 503Instructions for temporarily disabling these protection mechanisms can be 504found in the 505.Xr geom 4 506man page. 507