dd(1)dd(1)NAMEdd - Converts and copies a file
SYNOPSISdd [option=value...]
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
dd: XCU5.0, SVID 4
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: Spec‐
ifies the input file name; standard input is the default. Specifies
the output file name; standard output is the default. For the above
operands, the application must supply an expression specifying a size
in bytes. The expression, expr can be: a positive decimal number a pos‐
itive decimal number followed by k specifying mutiplication by 1024 a
positive decimal number followed by b specifying multiplication by 512
two or more positive decimal numbers with or without k or b separated
by x, specifying the product of the indicated values.
All the operands will be processed before any input is read.
Skips number input records before starting copy. [Tru64
UNIX] Copies number input files before terminating (makes sense
only where input is a magnetic tape or similar device). [Tru64
UNIX] Seeks to the Nth record from the beginning of input file
before copying. [Tru64 UNIX] Seeks to the Nth record from the
beginning of output file before copying. Same as seek=number.
Seeks to the Nth 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 charac‐
ters upper case. Swaps every pair of bytes. Does not stop pro‐
cessing on an error. Pads every input record to ibs. [Tru64
UNIX] Creates a sparse output file as described in AdvFS Admin‐
istration. 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
[Tru64 UNIX] To copy to a raw disk, the disk label must first be
zeroed using the disklabel -z command. For example: # disklabel -r
/dev/rdisk/dsk1a # disklabel -z /dev/rdisk/dsk1a disklabel: Disk
/dev/rdisk/dsk1a is unlabeled
[Tru64 UNIX] 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 uni‐
versal standard for EBCDIC/ASCII translation. [Tru64 UNIX] One
must specify conv=noerror,sync when copying raw disks with bad
sectors to ensure dd stays synchronized. [Tru64 UNIX] 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. [Tru64 UNIX] 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. [Tru64 UNIX] If option bs is used (or bs is
equal to obs) and no conversion is specified, then dd is partic‐
ularly efficient since less memory copies are done. [Tru64
UNIX] 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.
[Tru64 UNIX] In order to make use of tape multivolumes, the
files option must be used.
Security Note
[Tru64 UNIX] Any file system archive that contains ACLs (access con‐
trol lists) that was created using dd is not exportable unless the tar‐
get 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/tape/tape0_d0 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: Pro‐
vides 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 vari‐
ables contain an invalid setting, the utility behaves as if none of the
variables had been defined. If set to a non-empty string value, over‐
rides 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 multi‐
byte characters in arguments). Determines the locale for the format
and contents of diagnostic messages written to standard error. Deter‐
mines the location of message catalogues for the processing of LC_MES‐
SAGES.
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
dd(1)
