Provided by: sg3-utils_1.48-2ubuntu1_amd64 
NAME
sgm_dd - copy data to and from files and devices, especially SCSI devices
SYNOPSIS
sgm_dd [bs=BS] [count=COUNT] [ibs=BS] [if=IFILE] [iflag=FLAGS] [obs=BS] [of=OFILE] [oflag=FLAGS]
[seek=SEEK] [skip=SKIP] [--help] [--version]
[bpt=BPT] [cdbsz=6|10|12|16] [dio=0|1] [sync=0|1] [time=0|1] [verbose=VERB] [--dry-run] [--progress]
[--verbose]
DESCRIPTION
Copy data to and from any files. Specialized for "files" that are Linux SCSI generic (sg) devices and raw
devices. Uses memory mapped transfers on sg devices. Similar syntax and semantics to dd(1) but does not
perform any conversions.
Will only perform memory mapped transfers when IFILE or OFILE are SCSI generic (sg) devices.
If both IFILE and OFILE are sg devices then memory mapped transfers are performed on IFILE. If no other
flags are specified then indirect IO is performed on OFILE. If 'oflag=dio' is given then direct IO is
attempted on OFILE. If direct IO is not available, then this utility falls back to indirect IO and
reports this at the end of the copy.
The first group in the synopsis above are "standard" Unix dd(1) operands. The second group are extra
options added by this utility. Both groups are defined below.
OPTIONS
bpt=BPT
each IO transaction will be made using BPT blocks (or less if near the end of the copy). Default
is 128 for block sizes less that 2048 bytes, otherwise the default is 32. So for bs=512 the reads
and writes will each convey 64 KiB of data by default (less if near the end of the transfer or
memory restrictions). When cd/dvd drives are accessed, the block size is typically 2048 bytes and
bpt defaults to 32 which again implies 64 KiB transfers.
bs=BS where BS 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). For this utility the maximum size of
each individual IO operation is BS * BPT bytes.
cdbsz=6 | 10 | 12 | 16
size of SCSI READ and/or WRITE commands issued on sg device names. Default is 10 byte SCSI
command blocks (unless calculations indicate that a 4 byte block number may be exceeded, in which
case it defaults to 16 byte SCSI commands).
count=COUNT
copy COUNT blocks from IFILE to OFILE. Default is the minimum (of IFILE and OFILE) number of
blocks that sg devices report from SCSI READ CAPACITY commands or that block devices (or their
partitions) report. Normal files are not probed for their size. If skip=SKIP or seek=SEEK are
given and the count is derived (i.e. not explicitly given) then the derived count is scaled back
so that the copy will not overrun the device. If the file name is a block device partition and
COUNT is not given then the size of the partition rather than the size of the whole device is
used. If COUNT is not given and cannot be derived then an error message is issued and no copy
takes place.
dio=0 | 1
permits direct IO to be selected on the write-side (i.e. on OFILE). Only allowed when the
read-side (i.e. IFILE) is a sg device. When 1 there may be a "zero copy" copy (i.e. mmap-ed
transfer on the read into the user space and direct IO from there on the write, potentially two
DMAs and no data copying from the CPU). Default is 0. The same action as 'dio=1' is also
available with 'oflag=dio'.
ibs=BS if given must be the same as BS given to 'bs=' option.
if=IFILE
read from IFILE instead of stdin. If IFILE is '-' then stdin is read. Starts reading at the
beginning of IFILE unless SKIP is given.
iflag=FLAGS
where FLAGS is a comma separated list of one or more flags outlined below. These flags are
associated with IFILE and are ignored when IFILE is stdin.
obs=BS if given must be the same as BS given to 'bs=' option.
of=OFILE
write to OFILE instead of stdout. If OFILE is '-' then writes to stdout. If OFILE is /dev/null
then no actual writes are performed. If OFILE is '.' (period) then it is treated the same way as
/dev/null (this is a shorthand notation). If OFILE exists then it is _not_ truncated; it is
overwritten from the start of OFILE unless 'oflag=append' or SEEK is given.
oflag=FLAGS
where FLAGS is a comma separated list of one or more flags outlined below. These flags are
associated with OFILE and are ignored when OFILE is /dev/null, '.' (period), or stdout.
seek=SEEK
start writing SEEK bs-sized blocks from the start of OFILE. Default is block 0 (i.e. start of
file).
skip=SKIP
start reading SKIP bs-sized blocks from the start of IFILE. Default is block 0 (i.e. start of
file).
sync=0 | 1
when 1, does SYNCHRONIZE CACHE command on OFILE at the end of the transfer. Only active when OFILE
is a sg device file name.
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.
verbose=VERB
as VERB increases so does the amount of debug output sent to stderr. Default value is zero which
yields the minimum amount of debug output. A value of 1 reports extra information that is not
repetitive. A value 2 reports cdbs and responses for SCSI commands that are not repetitive (i.e.
other that READ and WRITE). Error processing is not considered repetitive. Values of 3 and 4 yield
output for all SCSI commands (and Unix read() and write() calls) so there can be a lot of output.
-d, --dry-run
does all the command line parsing and preparation but bypasses the actual copy or read. That
preparation may include opening IFILE or OFILE to determine their lengths. This option may be
useful for testing the syntax of complex command line invocations in advance of executing them.
-h, --help
outputs usage message and exits.
-p, --progress
this option causes a progress report to be output every two minutes until the copy is complete.
After the copy is complete a line with "completed" is printed to distinguish the final report from
the prior progress reports. When used twice the progress report is every minute, when used three
times the progress report is every 30 seconds.
If this option is given then the 'time=1' option is set implicitly.
-v, --verbose
when used once, this is equivalent to verbose=1. When used twice (e.g. "-vv") this is equivalent
to verbose=2, etc.
-V, --version
outputs version number information and exits.
FLAGS
Here is a list of flags and their meanings:
append causes the O_APPEND flag to be added to the open of OFILE. For normal files this will lead to data
appended to the end of any existing data. Cannot be used together with the seek=SEEK option as
they conflict. The default action of this utility is to overwrite any existing data from the
beginning of the file or, if SEEK is given, starting at block SEEK. Note that attempting to
'append' to a device file (e.g. a disk) will usually be ignored or may cause an error to be
reported.
dio is only active with oflag (i.e. 'oflag=dio'). Its action is described in the 'dio=1' option
description above.
direct causes the O_DIRECT flag to be added to the open of IFILE and/or OFILE. This flag requires some
memory alignment on IO. Hence user memory buffers are aligned to the page size. Has no effect on
sg, normal or raw files.
dpo set the DPO bit (disable page out) in SCSI READ and WRITE commands. Not supported for 6 byte cdb
variants of READ and WRITE. Indicates that data is unlikely to be required to stay in device (e.g.
disk) cache. May speed media copy and/or cause a media copy to have less impact on other device
users.
dsync causes the O_SYNC flag to be added to the open of IFILE and/or OFILE. The "d" is prepended to
lower confusion with the 'sync=0|1' option which has another action (i.e. a synchronisation to
media at the end of the transfer).
excl causes the O_EXCL flag to be added to the open of IFILE and/or OFILE.
fua causes the FUA (force unit access) bit to be set in SCSI READ and/or WRITE commands. This only has
effect with sg devices. The 6 byte variants of the SCSI READ and WRITE commands do not support the
FUA bit. Only active for sg device file names.
null has no affect, just a placeholder.
RETIRED OPTIONS
Here are some retired options that are still present:
fua=0 | 1 | 2 | 3
force unit access bit. When 3, fua is set on both IFILE and OFILE; when 2, fua is set on IFILE;
when 1, fua is set on OFILE; when 0 (default), fua is cleared on both. See the 'fua' flag.
NOTES
A raw device must be bound to a block device prior to using sgm_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
the lsscsi utility before use.
Raw device partition information can often be found with fdisk(8) [the "-ul" argument is useful in this
respect].
Various numeric arguments (e.g. SKIP) may include multiplicative suffixes or be given in hexadecimal. See
the "NUMERIC ARGUMENTS" section in the sg3_utils(8) man page.
The count, skip and seek parameters can take 64 bit values (i.e. very big numbers). Other values are
limited to what can fit in a signed 32 bit number.
Data usually gets to the user space in a 2 stage process: first the SCSI adapter DMAs into kernel buffers
and then the sg driver copies this data into user memory (write operations reverse this sequence). With
memory mapped transfers a kernel buffer reserved by sg is memory mapped (see the mmap(2) system call)
into the user space. When this is done the second (redundant) copy from kernel buffers to user space is
not needed. Hence the transfer is faster and requires less "grunt" from the CPU.
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.
For sg devices this utility issues SCSI READ and WRITE (SBC) commands which are appropriate for disks and
reading from CD/DVD/BD drives. Those commands are not formatted correctly for tape devices so sgm_dd
should not be used on tape devices.
This utility stops the copy if any error is encountered. For more advanced "copy on error" logic see the
sg_dd utility (and its 'coe' flag).
EXAMPLES
See the examples given in the man page for sg_dd(8).
SIGNALS
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.
EXIT STATUS
The exit status of sgm_dd is 0 when it is successful. Otherwise see the sg3_utils(8) man page. Since this
utility works at a higher level than individual commands, and there are 'coe' and 'retries' flags,
individual SCSI command failures do not necessary cause the process to exit.
AUTHORS
Written by Douglas Gilbert and Peter Allworth.
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright © 2000-2023 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.
SEE ALSO
The simplest variant of this utility is called sg_dd. A POSIX threads version of this utility called
sgp_dd is in the sg3_utils package. The lmbench package contains lmdd which is also interesting. dd(1),
ddpt(ddpt), raw(8)
sg3_utils-1.48 February 2023 SGM_DD(8)