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


       sg_dd - copies data to and from files and devices. Specialised for devices that understand
       the SCSI command set.


       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] [--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] [-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)  but  only  one  type  of
       "conversion" is supported. That optional conversion is sparse writing of the output file.

       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.


       blk_sgio=0 | 1
              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 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. 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 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

       cdbsz=6 | 10 | 12 | 16
              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

       coe=0 | 1 | 2 | 3
              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.

              only one conversion is permitted: sparse writing of the OFILE.  This option has the
              same  action  as  'oflag=sparse'. This alternate syntax was added for FreeBSD which
              uses this syntax in its dd command.  See the FLAGS 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.

       dio=0 | 1
              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.

       odir=0 | 1
              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).

       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 or a block device  and  'blk_sgio=1'  is

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

       --help outputs usage message and exits.

              outputs version number information and exits.

       -V     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 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 Doug Gilbert and Peter Allworth.


       Report bugs to <dgilbert at interlog dot com>.


       Copyright © 2000-2010 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

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