Provided by: sg3-utils_1.44-1ubuntu1_amd64 bug


       sg_dd - copy data to and from files and devices, especially SCSI devices


       sg_dd   [bs=BS]  [conv=CONV]  [count=COUNT]  [ibs=BS]  [if=IFILE]  [iflag=FLAGS]  [obs=BS]
       [of=OFILE] [oflag=FLAGS] [seek=SEEK] [skip=SKIP] [--help] [--verbose] [--version]

       [blk_sgio={0|1}] [bpt=BPT] [cdbsz={6|10|12|16}] [coe={0|1|2|3}] [coe_limit=CL] [dio={0|1}]
       [odir={0|1}]   [of2=OFILE2]   [retries=RETR]   [sync={0|1}]   [time={0|1}]  [verbose=VERB]
       [--dry-run] [-V]


       Copy data to and from any files. Specialized for "files" that are Linux SCSI generic  (sg)
       devices,  raw  devices or other devices that support the SG_IO ioctl (which are only found
       in the lk 2.6 series). Similar syntax and semantics to dd(1) command.

       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.

       This  utility  is  only  supported  on Linux whereas most other utilities in the sg3_utils
       package have been ported to other operating systems. A utility called "ddpt"  has  similar
       syntax  and  functionality  to sg_dd. ddpt drops some Linux specific features while adding
       some other generic features. This allows ddpt to be ported to other operating systems.


              when set to 0, block devices (e.g. /dev/sda) are treated like  normal  files  (i.e.
              read(2)  and write(2) are used for IO). When set to 1, block devices are assumed to
              accept the SG_IO ioctl and SCSI commands are issued for IO. This is only  supported
              for  2.6 series kernels. Note that ATAPI devices (e.g. cd/dvd players) use the SCSI
              command set but ATA disks do not (unless there is a protocol  conversion  as  often
              occurs  in  the  USB  mass storage class). If the input or output device is a block
              device partition (e.g. /dev/sda3) then setting this  option  causes  the  partition
              information  to  be  ignored  (since  access is directly to the underlying device).
              Default is 0. See the 'sgio' flag.

              each IO transaction will be made using BPT blocks (or less if near the end  of  the
              copy).  Default  is 128 for logical 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 logical block size is typically 2048 bytes and  bpt
              defaults  to  32  which  again  implies  64 KiB transfers. The block layer when the
              blk_sgio=1 option is used has  relatively  low  upper  limits  for  transfer  sizes
              (compared to sg device nodes, see /sys/block/<dev_name>/queue/max_sectors_kb ).

       bs=BS  where BS must be the logical block size of the physical device (if either the input
              or output files are accessed via SCSI commands). 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

              size of SCSI READ and/or WRITE commands issued on sg device names (or block devices
              when  'iflag=sgio'  and/or 'oflag=sgio' is given).  Default is 10 byte SCSI command
              blocks (unless calculations indicate that a 4 byte block number may be exceeded  or
              BPT  is  greater  than  16  bits (65535), in which case it defaults to 16 byte SCSI

              set to 1 or more for continue on error. Only applies to errors  on  sg  devices  or
              block devices with the 'sgio' flag set. Thus errors on other files will stop sg_dd.
              Default is 0 which implies  stop  on  any  error.  See  the  'coe'  flag  for  more

              where  CL  is  the  maximum  number  of consecutive bad blocks stepped over (due to
              "coe>0") on reads before the copy terminates.  This  only  applies  when  IFILE  is
              accessed  via  the  SG_IO ioctl. The default is 0 which is interpreted as no limit.
              This option is meant to stop the copy soon after unrecorded media is detected while
              still offering "continue on error" capability.

              see the CONVERSIONS section below.

              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 (or count=-1) and  cannot  be  derived  then  an  error
              message is issued and no copy takes place.

              default  is  0  which  selects  indirect  (buffered)  IO  on sg devices. Value of 1
              attempts direct IO which, if not available, falls back to  indirect  IO  and  notes
              this  at  completion.  If direct IO is selected and /proc/scsi/sg/allow_dio has the
              value of 0 then a warning is issued (and indirect  IO  is  performed).   For  finer
              grain control use 'iflag=dio' or '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.

              when  set  to  one opens block devices (e.g. /dev/sda) with the O_DIRECT flag. User
              memory buffers are aligned to the page size when set. The default is  0  (i.e.  the
              O_DIRECT  flag  is not used). Has no effect on sg, normal or raw files. If blk_sgio
              is also set then both are honoured: block devices are opened with the O_DIRECT flag
              and SCSI commands are issued via the SG_IO ioctl.

              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.

              write output to OFILE2. The default action is not to do this additional write (i.e.
              when this option is not given). OFILE2 is assumed to be a normal  file  or  a  fifo
              (i.e. a named pipe). OFILE2 is opened for writing, created if necessary, and closed
              at the end of the transfer. If OFILE2 is  a  fifo  (named  pipe)  then  some  other
              command  should  be  consuming  that  data  (e.g.  'md5sum OFILE2'), otherwise this
              utility will block.

              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.

              sometimes retries at the host are useful, for example when  there  is  a  transport
              error.  When  RETR  is  greater than zero then SCSI READs and WRITEs are retried on
              error, RETR times. Default value is zero.

              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).

              when 1, does SYNCHRONIZE CACHE command on OFILE at the end of  the  transfer.  Only
              active  when  OFILE  is a sg device file name or a block device and 'blk_sgio=1' is

              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.
              This  only  occurs  for  scsi  generic  (sg)  devices  and  block  devices when the
              'blk_sgio=1' option is set.

       -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.


       One or more conversions can be given to the "conv=" option. If more  than  one  is  given,
       they  should  be  comma  separated.  sg_dd does not perform the traditional dd conversions
       (e.g. ASCII to EBCDIC). Recently added conversions overlap somewhat with the flags so some
       conversions are now supported by sg_dd.

              this  conversion is very close to "iflag=coe" and is treated as such. See the "coe"
              flag. Note that an error on OFILE will stop the copy.

              this conversion is accepted for compatibility with dd and ignored since the default
              action of this utility is not to truncate OFILE.

       null   has no affect, just a placeholder.

       sparse FreeBSD  supports  "conv=sparse"  so  the  same  syntax is supported in sg_dd.  See
              "sparse" in the FLAGS sections for more information.

       sync   is ignored by sg_dd. With dd it means supply zero fill (rather than  skip)  and  is
              typically  used  like  this  "conv=noerror,sync"  to have the same functionality as
              sg_dd's "iflag=coe".


       Here is a list of flags and their meanings:

       append causes the O_APPEND flag to be added to the open of OFILE. For regular  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.

       coe    continue  on  error.  Only  active  for  sg devices and block devices that have the
              'sgio' flag set. 'iflag=coe oflag=coe' and 'coe=1' are equivalent.  Use  this  flag
              twice  (e.g.  'iflag=coe,coe')  to  have  the same action as the 'coe=2'. A medium,
              hardware or blank check error while reading will re-read blocks prior  to  the  bad
              block,  then  try  to  recover  the  bad  block, supplying zeros if that fails, and
              finally reread the blocks after the bad block. A medium, hardware  or  blank  check
              error  while  writing  is  noted  and  ignored.  The recovery of the bad block when
              reading uses the SCSI READ LONG command if 'coe' given twice or more (also with the
              command  line  option  'coe=2').  Further, the READ LONG will set its CORRCT bit if
              'coe' given thrice. SCSI disks may automatically try and remap faulty sectors  (see
              the  AWRE  and  ARRE in the read write error recovery mode page (the sdparm utility
              can access and possibly change these attributes)). Errors occurring on other  files
              types will stop sg_dd.  Error messages are sent to stderr. This flag is similar
               o 'conv=noerror,sync' in the dd(1) utility. See note about READ LONG below.

       dio    request  the sg device node associated with this flag does direct IO.  If direct IO
              is not available, falls back to indirect IO and notes this at completion. If direct
              IO  is  selected  and  /proc/scsi/sg/allow_dio has the value of 0 then a warning is
              issued (and indirect IO is performed).

       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.  If  'iflag=sgio'  and/or
              'oflag=sgio'  is also set then both are honoured: block devices are opened with the
              O_DIRECT flag and SCSI commands are issued via the SG_IO ioctl.

       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.

       flock  after  opening  the associated file (i.e. IFILE and/or OFILE) an attempt is made to
              get an advisory exclusive lock with the flock() system call.  The  flock  arguments
              are "FLOCK_EX | FLOCK_NB" which will cause the lock to be taken if available else a
              "temporarily unavailable" error is generated. An exit status of 90 is  produced  in
              the latter case and no copy is done.

       fua    causes  the  FUA  (force  unit  access)  bit  to  be  set in SCSI READ and/or WRITE
              commands. This only has an effect with sg devices or block devices  that  have  the
              'sgio'  flag  set.  The  6 byte variants of the SCSI READ and WRITE commands do not
              support the FUA bit.

              use posix_fadvise() to advise corresponding file there is no need to fill the  file
              buffer with recently read or written blocks.

       null   has no affect, just a placeholder.

       sgio   causes  block  devices to be accessed via the SG_IO ioctl rather than standard UNIX
              read() and write() commands. When the SG_IO ioctl is used the SCSI READ  and  WRITE
              commands  are  used  directly  to move data. sg devices always use the SG_IO ioctl.
              This  flag  offers  finer  grain  control  compared  to  the  otherwise   identical
              'blk_sgio=1' option.

       sparse after  each  BS  * BPT byte segment is read from the input, it is checked for being
              all zeros. If so, nothing is written to the output file unless  this  is  the  last
              segment  of the transfer. This flag is only active with the oflag option. It cannot
              be used when the output is not seekable (e.g. stdout). It is ignored if the  output
              file  is  /dev/null  .   Note  that this utility does not remove the OFILE prior to
              starting to write to it. Hence it may be advantageous to manually remove the  OFILE
              if  it  is large prior to using oflag=sparse. The last segment is always written so
              regular files will show the same length and so programs  like  md5sum  and  sha1sum
              will  generate  the  same value regardless of whether oflag=sparse is given or not.
              This option may be used when the OFILE is a raw device but is probably only  useful
              if the device is known to contain zeros (e.g. a SCSI disk after a FORMAT command).


       Here are some retired options that are still present:

       append=0 | 1
              when  set,  equivalent to 'oflag=append'. When clear the action is to overwrite the
              existing file (if it exists); this is the default.  See the 'append' flag.

       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.


       Block  devices  (e.g.  /dev/sda  and  /dev/hda)  can  be  given  for  IFILE.   If  neither
       '-iflag=direct',  'iflag=sgio'  nor  'blk_sgio=1'  is given then normal block IO involving
       buffering and caching is performed. If only '-iflag=direct' is given  then  the  buffering
       and  caching  is  bypassed  (this  is  applicable to both SCSI devices and ATA disks).  If
       'iflag=sgio' or 'blk_sgio=1' is given then the SG_IO ioctl  is  used  on  the  given  file
       causing  SCSI commands to be sent to the device and that also bypasses most of the actions
       performed by the block layer (this is only applicable to SCSI devices, not ATA disks). The
       same applies for block devices given for OFILE.

       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 arguments 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).   This  is  called  "indirect IO" and there is a 'dio' option to
       select "direct IO" which will DMA directly into user memory. Due to  some  issues  "direct
       IO"  is disabled in the sg driver and needs a configuration change to activate it. This is
       typically done with 'echo 1 > /proc/scsi/sg/allow_dio'.

       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.

       Even if READ LONG succeeds on a "bad" block  when  'coe=2'  (or  'coe=3')  is  given,  the
       recovered  data  may not be useful. There are no guarantees that the user data will appear
       "as is" in the first 512 bytes.

       A raw device must be bound to a block device prior to using sg_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', or sg_map before use.

       Disk partition information can often be found with fdisk(8) [the "-ul" argument is  useful
       in this respect].

       For  sg devices (and block devices when blk_sgio=1 is given) this utility issues SCSI READ
       and WRITE (SBC) commands which are appropriate for disks and reading from CD/DVD/HD-DVD/BD
       drives. Those commands are not formatted correctly for tape devices so sg_dd should not be
       used on tape devices. If the largest block address of the requested transfer exceeds a  32
       bit  block  number (i.e 0xffff) then a warning is issued and the sg device is accessed via
       SCSI READ(16) and WRITE(16) commands.

       The attributes of a block device (partition) are ignored when 'blk_sgio=1' is used.  Hence
       the whole device is read (rather than just the second partition) by this invocation:

          sg_dd if=/dev/sdb2 blk_sgio=1 of=t bs=512


       Looks quite similar in usage to dd:

          sg_dd if=/dev/sg0 of=t bs=512 count=1MB

       This  will  copy 1 million 512 byte blocks from the device associated with /dev/sg0 (which
       should have 512 byte blocks) to a file called t.  Assuming /dev/sda and /dev/sg0  are  the
       same device then the above is equivalent to:

          dd if=/dev/sda iflag=direct of=t bs=512 count=1000000

       although  dd's  speed may improve if bs was larger and count was suitably reduced. The use
       of the 'iflag=direct' option bypasses the buffering and caching that is usually done on  a
       block device.

       Using a raw device to do something similar on a ATA disk:

          raw /dev/raw/raw1 /dev/hda
          sg_dd if=/dev/raw/raw1 of=t bs=512 count=1MB

       To copy a SCSI disk partition to an ATA disk partition:

          raw /dev/raw/raw2 /dev/hda3
          sg_dd if=/dev/sg0 skip=10123456 of=/dev/raw/raw2 bs=512

       This  assumes  a valid partition is found on the SCSI disk at the given skip block address
       (past the 5 GB point of that disk) and that the partition goes to  the  end  of  the  SCSI
       disk.  An  explicit count is probably a safer option. The partition is copied to /dev/hda3
       which is an offset into the ATA disk /dev/hda . The  exact  number  of  blocks  read  from
       /dev/sg0 are written to /dev/hda (i.e. no padding).

       To time a streaming read of the first 1 GB (2 ** 30 bytes) on a disk this utility could be

          sg_dd if=/dev/sg0 of=/dev/null bs=512 count=2m time=1

       On completion this will output a line like: "time to transfer  data  was  18.779506  secs,
       57.18 MB/sec". The "MB/sec" in this case is 1,000,000 bytes per second.

       The  'of2='  option  can  be  used to copy data and take a md5sum of it without needing to
       re-read the data:

         mkfifo fif
         md5sum fif &
         sg_dd if=/dev/sg3 iflag=coe of=sg3.img oflag=sparse of2=fif bs=512

       This will image /dev/sg3 (e.g. an unmounted disk) and place the contents in  the  (sparse)
       file  sg3.img  .  Without re-reading the data it will also perform a md5sum calculation on
       the image.


       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 sg_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.

       An additional exit status of 90 is generated if the flock flag is  given  and  some  other
       process holds the advisory exclusive lock.


       Written by Douglas Gilbert and Peter Allworth.


       Report bugs to <dgilbert at interlog dot com>.


       Copyright © 2000-2018 Douglas Gilbert
       This  software  is distributed under the GPL version 2. There is NO warranty; not even for


       There is a web page discussing sg_dd at

       A POSIX threads version of this utility called sgp_dd is in the sg3_utils package. Another
       version from that package is called sgm_dd and it uses memory mapped IO to speed transfers
       from sg devices.

       The lmbench package contains lmdd which is also interesting. For moving data to  and  from
       tapes see dt which is found at

       To  change  mode  parameters  that  effect  a SCSI device's caching and error recovery see

       To verify the data on the media or to verify it against some other copy of  the  data  see

       See also raw(8), dd(1), ddrescue(GNU), ddpt