Content-type: text/html Man page of dd

dd

Section: User Commands (1)
Index Return to Main Contents
 

NAME

dd - Converts and copies a file  

SYNOPSIS

dd [option=value...]


 

STANDARDS

Interfaces documented on this reference page conform to industry standards as follows:

dd:  XPG4, XPG4-UNIX

Refer to the standards(5) reference page for more information about industry standards and associated tags.
 

OPTIONS

None
 

OPERANDS

The option=value operand set may take any of the following forms: Specifies the input file name; standard input is the default. Specifies the output file name; standard output is the default. Specifies the input block size in bytes; the default is 512. Specifies the output block size in bytes; the default is 512. Specifies both the input and output block size, superseding ibs and obs. Specifies the conversion buffer size. Skips number input records before starting copy. [Compaq]  Copies number input files before terminating (makes sense only where input is a magnetic tape or similar device). [Compaq]  Seeks to the numberth record from the beginning of input file before copying. [Compaq]  Seeks to the numberth record from the beginning of output file before copying. Same as seek=number. Seeks to the numberth record from the beginning of output file before copying. Same as oseek=number. Copies only number input records. Specifies one or more of the following conversions: Converts EBCDIC to ASCII. Converts variable-length records to fixed-length. Converts ASCII to EBCDIC. Converts IBM-EBCDIC to ASCII. Performs a slightly different map of ASCII to EBCDIC. Converts fixed-length records to variable-length. Makes all alphabetic characters lower case. Makes all alphabetic characters upper case. Swaps every pair of bytes. Does not stop processing on an error. Pads every input record to ibs. [Compaq]  Creates a sparse output file as described in AdvFS Administration. Do not truncate the output file. Preserve blocks in the output file not explicitly written by this invocation of the dd utility. (See the of=output_file operand.) Allows several comma-separated conversions.
 

DESCRIPTION

The dd command reads the specified input file or standard input, does the specified conversions, and copies it to the specified output file or standard output. The input and output block size may be specified to take advantage of raw physical I/O. The terms block and record refer to the quantity of data read or written by dd in one operation and are not necessarily the same size as a disk block.

Where sizes are specified, a number of bytes is expected. A number may end with w, b, or k to specify multiplication by 2, 512, or 1024, respectively; a pair of numbers can be separated by an x to indicate a product.

The cbs specification is used if one of the following conversions is specified: ascii, unblock, ebcdic, ibm, or block. For the first two conversions, dd places characters in a conversion buffer of size cbs, converts these characters to ASCII, trims trailing spaces, and adds newline characters before sending data to the specified output. For the latter three cases, dd places ASCII characters in the conversion buffer, converts these characters to EBCDIC, and adds trailing spaces to create an output record of size cbs.

After it finishes, dd reports the number of whole and partial input and output blocks.
 

NOTES

[Compaq]  To copy to a raw disk, the disk label must first be zeroed using the disklabel -z command. For example: disklabel -z rz17

[Compaq]  If you do not zero out the disk label, dd fails with the following error message: dd write error: Read-only file system The ASCII/EBCDIC conversion tables are taken from the 256 character standard in the CACM November, 1968. There is no universal standard for EBCDIC/ASCII translation. [Compaq]  One must specify conv=noerror,sync when copying raw disks with bad sectors to ensure dd stays synchronized. [Compaq]  Certain combinations of arguments to conv= are permitted. However, the block or unblock option cannot be combined with ascii, ebcdic, or ibm. Invalid combinations silently ignore all but the last mutually exclusive keyword. [Compaq]  If you need to use dd to copy to a streaming tape and the data is an odd length (not a multiple of 512 bytes), you must use the conv=sync flag to fill the last record. Streaming tape devices permit only multiples of 512 bytes. [Compaq]  If option bs is used (or bs is equal to obs) and no conversion is specified, then dd is particularly efficient since less memory copies are done. [Compaq]  The dd command does not support floppy disk multivolumes, but it does support tape multivolumes. This means that when ENOSPC is returned while reading or writing a tape, dd will prompt the user for a new tape.
[Compaq]  In order to make use of tape multivolumes, the files option must be used.
 

Security Note

[Compaq]  Any file system archive that contains ACLs (access control lists) that was created using dd is not exportable unless the target system has the exact same password and group files. If there is a mismatch, incorrect access may be granted to a file or directory.
 

EXIT STATUS

The following exit values are returned: The input file was successfully copied. An error occurred
 

DIAGNOSTICS

This message specifies the number of full and partial records both read and written:

f+p records in f+p records out

The number of full records read or written (f) refers to the blocks of data of size ibs or obs. The number of partial records read or written (p) refers to the blocks of data smaller than ibs or obs.
 

EXAMPLES

To read an EBCDIC tape blocked ten 80-byte EBCDIC card images per record into the ASCII file x, enter: dd if=/dev/rmt0 of=x ibs=800 cbs=80 conv=ascii,lcase

Note the use of raw magnetic tape. The dd command is especially suited to I/O on the raw physical devices because it allows reading and writing in arbitrary record sizes. To convert an ASCII text file to EBCDIC, enter: dd if=text.ascii of=text.ebcdic conv=ebcdic
This converts text.ascii to EBCDIC representation, storing this in text.ebcdic.
 

ENVIRONMENT VARIABLES

The following environment variables affect the execution of dd: Provides a default value for the internationalization variables that are unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization variables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value, overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multibyte characters in arguments). Determines the locale for the format and contents of diagnostic messages written to standard error. Determines the location of message catalogues for the processing of LC_MESSAGES.
 

SEE ALSO

Commands:  cp(1), cpio(1), sed(1), tar(1), tr(1), trbsd(1)

Functions:  lseek(2)

Routines:  fseek(3)

Files:  ascii(5)

Standards:  standards(5)

Command and Shell User's Guide

AdvFS Administration


 

Index

NAME
SYNOPSIS
STANDARDS
OPTIONS
OPERANDS
DESCRIPTION
NOTES
Security Note
EXIT STATUS
DIAGNOSTICS
EXAMPLES
ENVIRONMENT VARIABLES
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 02:43:02 GMT, October 02, 2010