man > sgm_dd(8)

SGM_DD(8)                                     SG3_UTILS                                    SGM_DD(8)

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) 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  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) 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) [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) 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) 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).

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 © 2000-2019 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), ddpt(ddpt), raw(8)

sg3_utils-1.45                              February 2019                                  SGM_DD(8)