# phpman > man > sgm_dd(8) [SGM_DD(8)](https://www.chedong.com/phpMan.php/man/SGMDD/8/markdown) SG3_UTILS [SGM_DD(8)](https://www.chedong.com/phpMan.php/man/SGMDD/8/markdown) ## 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_] [_--verbose_] ## DESCRIPTION Copy data to and from any files. Specialized for "files" that are Linux SCSI generic (sg) de‐ vices and raw devices. Uses memory mapped transfers on sg devices. Similar syntax and seman‐ tics to [**dd(1)](https://www.chedong.com/phpMan.php/man/dd/1/markdown)** 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)](https://www.chedong.com/phpMan.php/man/dd/1/markdown)** 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)](https://www.chedong.com/phpMan.php/man/dd/1/markdown)** 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 ac‐ tive 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 in‐ formation that is not repetitive. A value 2 reports cdbs and responses for SCSI com‐ mands 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. ### -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 over‐ write 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 re‐ quires 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)](https://www.chedong.com/phpMan.php/man/raw/8/markdown)** for more in‐ formation 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)](https://www.chedong.com/phpMan.php/man/fdisk/8/markdown)** [the "-ul" argument is use‐ ful 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)](https://www.chedong.com/phpMan.php/man/sg3utils/8/markdown) 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 re‐ verse this sequence). With memory mapped transfers a kernel buffer reserved by sg is memory mapped (see the [**mmap(2)](https://www.chedong.com/phpMan.php/man/mmap/2/markdown)** system call) into the user space. When this is done the second (re‐ dundant) 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)](https://www.chedong.com/phpMan.php/man/dd/8/markdown).** ## 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)](https://www.chedong.com/phpMan.php/man/sg3utils/8/markdown) 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 . ## COPYRIGHT Copyright © 2000-2019 Douglas Gilbert This software is distributed under the GPL version 2. There is NO warranty; not even for MER‐ CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. ## SEE ALSO The simplest variant of this utility is called **sg**___**dd.** A POSIX threads version of this util‐ ity called **sgp**___**dd** is in the sg3_utils package. The lmbench package contains **lmdd** which is also interesting. [**dd(1)](https://www.chedong.com/phpMan.php/man/dd/1/markdown),** **ddpt(ddpt),** [**raw(8)](https://www.chedong.com/phpMan.php/man/raw/8/markdown)** sg3_utils-1.45 February 2019 [SGM_DD(8)](https://www.chedong.com/phpMan.php/man/SGMDD/8/markdown)