Provided by: sg3-utils_1.33-1_amd64 bug


       sgm_dd  -  copies  data  to  and  from  files  and  devices.  Specialized for devices that
       understand the SCSI command set and does memory mapped transfers from sg devices.


       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]


       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)

       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 'oflag=smmap' is given  then
       shared mmap-ed IO (sharing the mmap-ed reserve buffer associated with IFILE) is attempted.
       In both latter cases if the faster IO option is not available, they fall back to  indirect
       IO and report 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.


              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

       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).

              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 skip=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.

              read  from  IFILE  instead  of  stdin.  If  IFILE is '-' then stdin is read. Starts
              reading at the beginning of IFILE unless SKIP is given.

              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.

              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.

              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.

              start  writing  SEEK  bs-sized  blocks from the start of OFILE.  Default is block 0
              (i.e. start of file).

              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.

              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.

       --help outputs usage message and exits.

              outputs version number information and exits.


       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

       null   has no affect, just a placeholder.

       smmap  is only active for oflag. It sets shared mmap IO usage on  OFILE  if  it  is  a  sg
              device  node.  The  IFILE also needs to be a sg device node (or there is no mmap-ed
              reserve buffer to share).


       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.


       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 'cat /proc/scsi/scsi' 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).


       See the examples given in the man page for sg_dd(8).


       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.


       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.


       Written by Doug Gilbert and Peter Allworth.


       Report bugs to <dgilbert at interlog dot com>.


       Copyright © 2000-2009 Douglas Gilbert
       This  software  is distributed under the GPL version 2. There is NO warranty; not even for


       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.  raw(8), dd(1)