HP UX Operating Systems 202

dd(1)

Note the use of the raw magnetic tape device ®le. dd is especially suited to I/O on raw physical devices because it allows reading and writing in arbitrary block sizes.

WARNINGS

Some devices, such as 1/2-inch magnetic tapes, are incapable of seeking. Such devices may be positioned prior to running dd by using mt(1) or some other appropriate command. The skip, seek, iseek and oseek options do work for such devices. However, skipping blocks using these options is slow on devices that cannot seek, since the blocks must actually be read to get to the desired position on the tape.

ASCII and EBCDIC conversion tables are taken from the 256-character ACM standard, Nov, 1968. The ibm conversion, while less widely accepted as a standard, corresponds better to certain IBM print train conventions. There is no universal solution.

Newline characters are inserted only on conversion to ASCII; padding is done only on conversion to EBCDIC. These should be separate options.

If if or of refers to a raw disk, bs should always be a multiple of the sector size of the disk. By default, bs is 512 bytes. If the sector size of the disk is different from 512 bytes, bs should be speci®ed using a multiple of sector size. The character special (raw) device ®le should always be used for devices.

It is entirely up to the user to insure there is enough room in the destination ®le, ®le system and/or device to contain the output since dd cannot pre-determine the required space after conversion.