Provided by: sg3-utils_1.36-1ubuntu1_amd64 bug

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]

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 '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.

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  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.

       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.

       --help outputs usage message and exits.

       --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.

       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).

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 '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).

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 © 2000-2012 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.  raw(8), dd(1)