What is the 'bs' option in dd?
I've found conflicting information on the internet on whether the bs in a command like dd bs=512 if=/home/Downloads/ubuntu.iso of=/dev/sdb stands for "bytes per second" or "block size". I couldn't find anything in the man pages, as the only reference to bs is:
2bs=BYTES
read and write up to BYTES bytes at a time
1 Answer
As with other GNU Coreutils utilities, the primary documentation is the info page.
From info coreutils dd invocation :
‘bs=BYTES’ Set both input and output block sizes to BYTES. This makes ‘dd’ read and write BYTES per block, overriding any ‘ibs’ and ‘obs’ settings. In addition, if no data-transforming ‘conv’ option is specified, input is copied to the output as soon as it’s read, even if it is smaller than the block size.There are corresponding parameters for the individual read, write and conversion block sizes:
‘ibs=BYTES’ Set the input block size to BYTES. This makes ‘dd’ read BYTES per block. The default is 512 bytes.
‘obs=BYTES’ Set the output block size to BYTES. This makes ‘dd’ write BYTES per block. The default is 512 bytes.
‘cbs=BYTES’ Set the conversion block size to BYTES. When converting variable-length records to fixed-length ones (‘conv=block’) or the reverse (‘conv=unblock’), use BYTES as the fixed record length.
