dd is used to copy raw data from source to sink, where source and sink can be a block device, file or piped input/output.
As part of the GNU sys-apps/coreutils, is installed in any standard any Gentoo GNU/Linux system.
In the event that coreutils goes missing:
emerge --ask sys-apps/coreutils
By default dd takes input from stdin, optionally manipulates the data, and writes to stdout.
Some common tasks where dd is used:
This should work with any live media as long as the memory stick /dev/sdX is large enough.
Any data on the memory stick will be lost.
dd if=/home/myLiveCD.iso of=/dev/sdX bs=8M
if: Defines the source.
of: Defines the sink.
bs: Defines the block size (amount of data read/written at a time). The default is 512 bytes but most modern devices can read/write much faster. It is possible to define different sizes for source and sink using
Master boot record backup
To backup the master boot record (MBR), copy only the first 512 bytes:
dd if=/dev/sdX of=/root/mbr.bin bs=512 count=1
count: The number of blocks to copy.
This is the complete MBR with the partition layout.
As an example, convert any upper case character in a file to lowercase and reverse the input per line, then pipe the output to less to display the file:
dd if=/etc/portage/make.conf conv=swab,lcase,noerror | less
conv=swab: Revert the input per line by swapping any input byte (writing backwards).
conv=lcase: Convert any upper case letter to lower case. To convert lower case to upper case use
conv=noerror: Continue if a read error occurs.