{ "mode": "man", "parameter": "sgm_dd", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/sgm_dd/8/json", "generated": "2026-06-15T16:42:57Z", "synopsis": "sgmdd [bs=BS] [count=COUNT] [ibs=BS] [if=IFILE] [iflag=FLAGS] [obs=BS] [of=OFILE]\n[oflag=FLAGS] [seek=SEEK] [skip=SKIP] [--help] [--version]\n[bpt=BPT] [cdbsz=6|10|12|16] [dio=0|1] [sync=0|1] [time=0|1] [verbose=VERB] [--dry-run]\n[--verbose]", "sections": { "NAME": { "content": "sgmdd - copy data to and from files and devices, especially SCSI devices\n", "subsections": [] }, "SYNOPSIS": { "content": "sgmdd [bs=BS] [count=COUNT] [ibs=BS] [if=IFILE] [iflag=FLAGS] [obs=BS] [of=OFILE]\n[oflag=FLAGS] [seek=SEEK] [skip=SKIP] [--help] [--version]\n\n[bpt=BPT] [cdbsz=6|10|12|16] [dio=0|1] [sync=0|1] [time=0|1] [verbose=VERB] [--dry-run]\n[--verbose]\n", "subsections": [] }, "DESCRIPTION": { "content": "Copy data to and from any files. Specialized for \"files\" that are Linux SCSI generic (sg) de‐\nvices and raw devices. Uses memory mapped transfers on sg devices. Similar syntax and seman‐\ntics to dd(1) but does not perform any conversions.\n\nWill only perform memory mapped transfers when IFILE or OFILE are SCSI generic (sg) devices.\n\nIf both IFILE and OFILE are sg devices then memory mapped transfers are performed on IFILE.\nIf no other flags are specified then indirect IO is performed on OFILE. If 'oflag=dio' is\ngiven then direct IO is attempted on OFILE. If direct IO is not available, then this utility\nfalls back to indirect IO and reports this at the end of the copy.\n\nThe first group in the synopsis above are \"standard\" Unix dd(1) operands. The second group\nare extra options added by this utility. Both groups are defined below.\n", "subsections": [] }, "OPTIONS": { "content": "bpt=BPT\neach IO transaction will be made using BPT blocks (or less if near the end of the\ncopy). Default is 128 for block sizes less that 2048 bytes, otherwise the default is\n32. So for bs=512 the reads and writes will each convey 64 KiB of data by default\n(less if near the end of the transfer or memory restrictions). When cd/dvd drives are\naccessed, the block size is typically 2048 bytes and bpt defaults to 32 which again\nimplies 64 KiB transfers.\n\nbs=BS where BS must be the block size of the physical device. Note that this differs from\ndd(1) which permits BS to be an integral multiple. Default is 512 which is usually\ncorrect for disks but incorrect for cdroms (which normally have 2048 byte blocks). For\nthis utility the maximum size of each individual IO operation is BS * BPT bytes.\n\ncdbsz=6 | 10 | 12 | 16\nsize of SCSI READ and/or WRITE commands issued on sg device names. Default is 10 byte\nSCSI command blocks (unless calculations indicate that a 4 byte block number may be\nexceeded, in which case it defaults to 16 byte SCSI commands).\n\ncount=COUNT\ncopy COUNT blocks from IFILE to OFILE. Default is the minimum (of IFILE and OFILE)\nnumber of blocks that sg devices report from SCSI READ CAPACITY commands or that block\ndevices (or their partitions) report. Normal files are not probed for their size. If\nskip=SKIP or seek=SEEK are given and the count is derived (i.e. not explicitly given)\nthen the derived count is scaled back so that the copy will not overrun the device. If\nthe file name is a block device partition and COUNT is not given then the size of the\npartition rather than the size of the whole device is used. If COUNT is not given and\ncannot be derived then an error message is issued and no copy takes place.\n\ndio=0 | 1\npermits direct IO to be selected on the write-side (i.e. on OFILE). Only allowed when\nthe read-side (i.e. IFILE) is a sg device. When 1 there may be a \"zero copy\" copy\n(i.e. mmap-ed transfer on the read into the user space and direct IO from there on the\nwrite, potentially two DMAs and no data copying from the CPU). Default is 0. The same\naction as 'dio=1' is also available with 'oflag=dio'.\n\nibs=BS if given must be the same as BS given to 'bs=' option.\n\nif=IFILE\nread from IFILE instead of stdin. If IFILE is '-' then stdin is read. Starts reading\nat the beginning of IFILE unless SKIP is given.\n\niflag=FLAGS\nwhere FLAGS is a comma separated list of one or more flags outlined below. These\nflags are associated with IFILE and are ignored when IFILE is stdin.\n\nobs=BS if given must be the same as BS given to 'bs=' option.\n\nof=OFILE\nwrite to OFILE instead of stdout. If OFILE is '-' then writes to stdout. If OFILE is\n/dev/null then no actual writes are performed. If OFILE is '.' (period) then it is\ntreated the same way as /dev/null (this is a shorthand notation). If OFILE exists then\nit is not truncated; it is overwritten from the start of OFILE unless 'oflag=append'\nor SEEK is given.\n\noflag=FLAGS\nwhere FLAGS is a comma separated list of one or more flags outlined below. These\nflags are associated with OFILE and are ignored when OFILE is /dev/null, '.' (period),\nor stdout.\n\nseek=SEEK\nstart writing SEEK bs-sized blocks from the start of OFILE. Default is block 0 (i.e.\nstart of file).\n\nskip=SKIP\nstart reading SKIP bs-sized blocks from the start of IFILE. Default is block 0 (i.e.\nstart of file).\n\nsync=0 | 1\nwhen 1, does SYNCHRONIZE CACHE command on OFILE at the end of the transfer. Only ac‐\ntive when OFILE is a sg device file name.\n\ntime=0 | 1\nwhen 1, times transfer and does throughput calculation, outputting the results (to\nstderr) at completion. When 0 (default) doesn't perform timing.\n\nverbose=VERB\nas VERB increases so does the amount of debug output sent to stderr. Default value is\nzero which yields the minimum amount of debug output. A value of 1 reports extra in‐\nformation that is not repetitive. A value 2 reports cdbs and responses for SCSI com‐\nmands that are not repetitive (i.e. other that READ and WRITE). Error processing is\nnot considered repetitive. Values of 3 and 4 yield output for all SCSI commands (and\nUnix read() and write() calls) so there can be a lot of output.\n", "subsections": [ { "name": "-d --dry-run", "content": "does all the command line parsing and preparation but bypasses the actual copy or\nread. That preparation may include opening IFILE or OFILE to determine their lengths.\nThis option may be useful for testing the syntax of complex command line invocations\nin advance of executing them.\n", "flag": "-d", "long": "--dry-run" }, { "name": "-h --help", "content": "outputs usage message and exits.\n", "flag": "-h", "long": "--help" }, { "name": "-v --verbose", "content": "when used once, this is equivalent to verbose=1. When used twice (e.g. \"-vv\") this is\nequivalent to verbose=2, etc.\n", "flag": "-v", "long": "--verbose" }, { "name": "-V --version", "content": "outputs version number information and exits.\n", "flag": "-V", "long": "--version" } ] }, "FLAGS": { "content": "Here is a list of flags and their meanings:\n\nappend causes the OAPPEND flag to be added to the open of OFILE. For normal files this will\nlead to data appended to the end of any existing data. Cannot be used together with\nthe seek=SEEK option as they conflict. The default action of this utility is to over‐\nwrite any existing data from the beginning of the file or, if SEEK is given, starting\nat block SEEK. Note that attempting to 'append' to a device file (e.g. a disk) will\nusually be ignored or may cause an error to be reported.\n\ndio is only active with oflag (i.e. 'oflag=dio'). Its action is described in the 'dio=1'\noption description above.\n\ndirect causes the ODIRECT flag to be added to the open of IFILE and/or OFILE. This flag re‐\nquires some memory alignment on IO. Hence user memory buffers are aligned to the page\nsize. Has no effect on sg, normal or raw files.\n\ndpo set the DPO bit (disable page out) in SCSI READ and WRITE commands. Not supported for\n6 byte cdb variants of READ and WRITE. Indicates that data is unlikely to be required\nto stay in device (e.g. disk) cache. May speed media copy and/or cause a media copy\nto have less impact on other device users.\n\ndsync causes the OSYNC flag to be added to the open of IFILE and/or OFILE. The \"d\" is\nprepended to lower confusion with the 'sync=0|1' option which has another action (i.e.\na synchronisation to media at the end of the transfer).\n\nexcl causes the OEXCL flag to be added to the open of IFILE and/or OFILE.\n\nfua causes the FUA (force unit access) bit to be set in SCSI READ and/or WRITE commands.\nThis only has effect with sg devices. The 6 byte variants of the SCSI READ and WRITE\ncommands do not support the FUA bit. Only active for sg device file names.\n\nnull has no affect, just a placeholder.\n", "subsections": [] }, "RETIRED OPTIONS": { "content": "Here are some retired options that are still present:\n\nfua=0 | 1 | 2 | 3\nforce unit access bit. When 3, fua is set on both IFILE and OFILE; when 2, fua is set\non IFILE; when 1, fua is set on OFILE; when 0 (default), fua is cleared on both. See\nthe 'fua' flag.\n", "subsections": [] }, "NOTES": { "content": "A raw device must be bound to a block device prior to using sgmdd. See raw(8) for more in‐\nformation about binding raw devices. To be safe, the sg device mapping to SCSI block devices\nshould be checked with the lsscsi utility before use.\n\nRaw device partition information can often be found with fdisk(8) [the \"-ul\" argument is use‐\nful in this respect].\n\nVarious numeric arguments (e.g. SKIP) may include multiplicative suffixes or be given in\nhexadecimal. See the \"NUMERIC ARGUMENTS\" section in the sg3utils(8) man page.\n\nThe count, skip and seek parameters can take 64 bit values (i.e. very big numbers). Other\nvalues are limited to what can fit in a signed 32 bit number.\n\nData usually gets to the user space in a 2 stage process: first the SCSI adapter DMAs into\nkernel buffers and then the sg driver copies this data into user memory (write operations re‐\nverse this sequence). With memory mapped transfers a kernel buffer reserved by sg is memory\nmapped (see the mmap(2) system call) into the user space. When this is done the second (re‐\ndundant) copy from kernel buffers to user space is not needed. Hence the transfer is faster\nand requires less \"grunt\" from the CPU.\n\nAll informative, warning and error output is sent to stderr so that dd's output file can be\nstdout and remain unpolluted. If no options are given, then the usage message is output and\nnothing else happens.\n\nFor sg devices this utility issues SCSI READ and WRITE (SBC) commands which are appropriate\nfor disks and reading from CD/DVD/BD drives. Those commands are not formatted correctly for\ntape devices so sgmdd should not be used on tape devices.\n\nThis utility stops the copy if any error is encountered. For more advanced \"copy on error\"\nlogic see the sgdd utility (and its 'coe' flag).\n", "subsections": [] }, "EXAMPLES": { "content": "See the examples given in the man page for sgdd(8).\n", "subsections": [] }, "SIGNALS": { "content": "The signal handling has been borrowed from dd: SIGINT, SIGQUIT and SIGPIPE output the number\nof remaining blocks to be transferred and the records in + out counts; then they have their\ndefault action. SIGUSR1 causes the same information to be output yet the copy continues.\nAll output caused by signals is sent to stderr.\n", "subsections": [] }, "EXIT STATUS": { "content": "The exit status of sgmdd is 0 when it is successful. Otherwise see the sg3utils(8) man\npage. Since this utility works at a higher level than individual commands, and there are\n'coe' and 'retries' flags, individual SCSI command failures do not necessary cause the\nprocess to exit.\n", "subsections": [] }, "AUTHORS": { "content": "Written by Douglas Gilbert and Peter Allworth.\n", "subsections": [] }, "REPORTING BUGS": { "content": "Report bugs to .\n", "subsections": [] }, "COPYRIGHT": { "content": "Copyright © 2000-2019 Douglas Gilbert\nThis software is distributed under the GPL version 2. There is NO warranty; not even for MER‐\nCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n", "subsections": [] }, "SEE ALSO": { "content": "The simplest variant of this utility is called sgdd. A POSIX threads version of this util‐\nity called sgpdd is in the sg3utils package. The lmbench package contains lmdd which is\nalso interesting. dd(1), ddpt(ddpt), raw(8)\n\n\n\nsg3utils-1.45 February 2019 SGMDD(8)", "subsections": [] } }, "summary": "sgmdd - copy data to and from files and devices, especially SCSI devices", "flags": [ { "flag": "-d", "long": "--dry-run", "arg": null, "description": "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." }, { "flag": "-h", "long": "--help", "arg": null, "description": "outputs usage message and exits." }, { "flag": "-v", "long": "--verbose", "arg": null, "description": "when used once, this is equivalent to verbose=1. When used twice (e.g. \"-vv\") this is equivalent to verbose=2, etc." }, { "flag": "-V", "long": "--version", "arg": null, "description": "outputs version number information and exits." } ], "examples": [ "See the examples given in the man page for sgdd(8)." ], "see_also": [ { "name": "dd", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/dd/1/json" }, { "name": "ddpt", "section": "ddpt", "url": "https://www.chedong.com/phpMan.php/man/ddpt/ddpt/json" }, { "name": "raw", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/raw/8/json" } ] }