dd: Image Copy

This utility is ``useful for making an image copy of any media. An image copy is an exact byte-for-byte copy" [][p. 80]RT:UNIX.

dd [if=input-file] [of=output-file] [option]

option can be one or more of:

• bs (block size): default is 512 bytes.
• conv=arg... where arg is one or more of the following, separated by commas:
  • ascii: convert EBCDIC to ASCII.
  • ebcdic: convert ASCII to EBCDIC.
  • swab: swap every pair of bytes.
  • noerror: do not stop processing on detecting an error.
  • sync: pad every input record to (default) 512 bytes.
• see your system manual for more details.

To read a older Silicon Graphics tape on a Sun, the dd command is:

dd if=/dev/tape conv=swab,noerror,sync | tar xf -

The input of dd is the file on the cartridge tape. dd converts that file by swapping every pair of bytes, and padding every record to 512 bytes (while not stopping if an error occurs). The resulting output file is fed (through the pipe) to tar, which then reads the file.

When an hyphen (-) is used instead of a file name on the tar command, the input is taken from the standard input on the extract and put to the standard ouput on the create command.