copies data to and from sg and raw devices

sg_dd [OPTION]...

Copy data to and from Linux SCSI generic (sg), raw devices or normal files. Similar syntax and semantics to dd(1) but does not perform any conversions.

bpt=BLOCKS

each IO transaction will be made using this number of blocks (or less if near the end of count). Default is 128.

bs=BYTES

this must be the block size of the physical device. Note that this differs from dd(1) which permits "bs" to be an integral multiple. Default is 512 which is usually correct for disks but incorrect for cdroms (which normally have 2048 byte blocks).

coe=0 | 1

set to 1 for continue on error: if reading assume zeros read, if writing then ignore and continue. Only applies to errors on sg devices (e.g. errors on normal files will stop sg_dd). Error messages are still sent to stderr. Default is 0 for do not continue on error

count=BLOCKS

copy this number of blocks. Default is minimum number that sg devices return from READ CAPACITY (if that works) or 0

ibs=BYTES

if given must be the same as bs

if=FILE

read from FILE instead of stdin. A file name of - is taken to be stdin

obs=BYTES

if given must be the same as bs

of=FILE

write to FILE instead of stdout. A file name of - is taken to be stdout

seek=BLOCKS

skip BLOCKS bs-sized blocks at start of output

skip=BLOCKS

skip BLOCKS bs-sized blocks at start of input

time=0 | 1

when 1, times transfer and does throughput calculation, outputting the results (to stderr) at completion. When 0 (default) doesn't perform timing

A raw device must be bound to a block device prior to using sg_dd. See raw(8) for more information about binding raw devices. To be safe, the sg device mapping to SCSI block devices should be checked with "cat /proc/scsi/scsi" before use.

The count is only deduced for sg devices (minimum > 0 if both input and output are sg devices) otherwise it defaults to 0. This is for safety! Raw device partition information can often be found with fdisk(8) [the "-ul" argument is useful in this respect].

BYTES and BLOCKS may be followed by the following multiplicative suffixes: c C *1; b B *512; k *1,024; K *1,000; m *1,048,576; M *1,000,000; g *1,073,741,824; and G *1,000,000,000

All informative, warning and error output is sent to stderr so that dd's output file can be stdout and remain unpolluted. If no options are given, then the usage message is output and nothing else happens.

Looks quite similar in usage to dd:

sg_dd if=/dev/sg0 of=t bs=512 count=1M

This will copy 1 million 512 byte blocks from the device associated with /dev/sg0 (which should have 512 byte blocks) to a file called t. Assuming /dev/sda and /dev/sg0 are the same device then the above is equivalent to:

dd if=/dev/sda of=t bs=512 count=1000000

although dd's speed may improve if bs was larger and count was suitably reduced. Using a raw device to do something similar on a IDE disk:

raw /dev/raw/raw1 /dev/hda

sg_dd if=/dev/raw/raw1 of=t bs=512 count=1M

To copy a SCSI disk partition to an IDE disk partition:

raw /dev/raw/raw2 /dev/hda3

sg_dd if=/dev/sg0 skip=10123456 of=/dev/raw/raw2 bs=512

This assumes a valid partition is found on the SCSI disk at the given skip block address (past the 5 GB point of that disk) and that the partition goes to the end of the SCSI disk. An explicit count is probably a safer option.

The signal handling has been borrowed from dd: SIGINT, SIGQUIT and SIGPIPE output the number of remaining blocks to be transferred and the records in + out counts; then they have their default action. SIGUSR1 causes the same information to be output yet the copy continues. All output caused by signals is sent to stderr.

Written by Doug Gilbert and Peter Allworth.

Report bugs to <dgilbert@interlog.com>.

Copyright © 2000 Douglas Gilbert

This software is distributed under the GPL version 2. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

A POSIX threads version of this command called sgp_dd is in the sg_utils package. The lmbench package contains lmdd which is also interesting. raw(8), dd(1)