As far as backup utilities go, the dd utility is about as featureless as they come. However, it has certain applications for which it is uniquely suited.
The basic syntax of dd is as follows:
The preceding options are used almost every time you run dd ; they are explained in the following sections.
The if= argument
specifies the input file or the file from which it is going to copy
the data. This is the file or raw partition that you are going to
back up (e.g., dd if=/dev/dsk/c0t0d0s0 or
dd if=/home/file). If you want
dd to look at
stdin for its
data, you don’t need this argument.
The of= argument specifies the output file or the
file to which you are sending the data. This could be a file on disk
or an optical platter, another raw partition, or a tape
drive (e.g., dd
of=/backup/file, dd of=/dev/rmt/0n). If
you are sending to
don’t need this argument.
The bs= argument specifies the block size, or the amount of data that is to be transferred in one I/O operation. This value normally is expressed in bytes, but in most versions dd also can be specified in kilobytes by adding a k at the end of the number (e.g., 10 K). (This is different from a blocking factor, like dump and tar use, which is multiplied by a fixed value known as the minimum block size. A blocking ...