1SGM_DD(8)                          SG3_UTILS                         SGM_DD(8)
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NAME

6       sgm_dd  -  copy  data  to  and  from files and devices, especially SCSI
7       devices
8

SYNOPSIS

10       sgm_dd [bs=BS] [count=COUNT] [ibs=BS] [if=IFILE] [iflag=FLAGS] [obs=BS]
11       [of=OFILE] [oflag=FLAGS] [seek=SEEK] [skip=SKIP] [--help] [--version]
12
13       [bpt=BPT]  [cdbsz=6|10|12|16]  [dio=0|1]  [sync=0|1]  [time=0|1]  [ver‐
14       bose=VERB] [--dry-run] [--verbose]
15

DESCRIPTION

17       Copy data to and from any files. Specialized for "files" that are Linux
18       SCSI generic (sg) devices and raw devices. Uses memory mapped transfers
19       on sg devices. Similar syntax and semantics to dd(1) but does not  per‐
20       form any conversions.
21
22       Will  only perform memory mapped transfers when IFILE or OFILE are SCSI
23       generic (sg) devices.
24
25       If both IFILE and OFILE are sg devices then memory mapped transfers are
26       performed on IFILE. If no other flags are specified then indirect IO is
27       performed on OFILE. If 'oflag=dio' is given then direct IO is attempted
28       on  OFILE.  If direct IO is not available, then this utility falls back
29       to indirect IO and reports this at the end of the copy.
30
31       The first group in the synopsis above are "standard" Unix  dd(1)  oper‐
32       ands.  The  second group are extra options added by this utility.  Both
33       groups are defined below.
34

OPTIONS

36       bpt=BPT
37              each IO transaction will be made using BPT blocks  (or  less  if
38              near  the  end of the copy). Default is 128 for block sizes less
39              that 2048 bytes, otherwise the default is 32. So for bs=512  the
40              reads  and  writes  will  each  convey 64 KiB of data by default
41              (less if near the end of the transfer or  memory  restrictions).
42              When  cd/dvd  drives  are  accessed, the block size is typically
43              2048 bytes and bpt defaults to 32 which  again  implies  64  KiB
44              transfers.
45
46       bs=BS  where  BS  must  be  the block size of the physical device. Note
47              that this differs from dd(1) which permits BS to be an  integral
48              multiple.  Default is 512 which is usually correct for disks but
49              incorrect for cdroms (which normally have 2048 byte blocks). For
50              this utility the maximum size of each individual IO operation is
51              BS * BPT bytes.
52
53       cdbsz=6 | 10 | 12 | 16
54              size of SCSI READ and/or WRITE  commands  issued  on  sg  device
55              names.   Default is 10 byte SCSI command blocks (unless calcula‐
56              tions indicate that a 4 byte block number may  be  exceeded,  in
57              which case it defaults to 16 byte SCSI commands).
58
59       count=COUNT
60              copy  COUNT  blocks  from IFILE to OFILE. Default is the minimum
61              (of IFILE and OFILE) number of blocks  that  sg  devices  report
62              from SCSI READ CAPACITY commands or that block devices (or their
63              partitions) report. Normal files are not probed for their  size.
64              If  skip=SKIP  or  skip=SEEK  are given and the count is derived
65              (i.e.  not explicitly given) then the derived  count  is  scaled
66              back  so  that the copy will not overrun the device. If the file
67              name is a block device partition and COUNT is not given then the
68              size  of  the partition rather than the size of the whole device
69              is used. If COUNT is not given and cannot  be  derived  then  an
70              error message is issued and no copy takes place.
71
72       dio=0 | 1
73              permits  direct  IO  to  be  selected on the write-side (i.e. on
74              OFILE).  Only allowed when the read-side (i.e. IFILE)  is  a  sg
75              device.  When  1  there  may be a "zero copy" copy (i.e. mmap-ed
76              transfer on the read into the user  space  and  direct  IO  from
77              there  on  the  write,  potentially two DMAs and no data copying
78              from the CPU). Default is 0.  The same action as 'dio=1' is also
79              available with 'oflag=dio'.
80
81       ibs=BS if given must be the same as BS given to 'bs=' option.
82
83       if=IFILE
84              read  from IFILE instead of stdin. If IFILE is '-' then stdin is
85              read. Starts reading at the beginning of IFILE  unless  SKIP  is
86              given.
87
88       iflag=FLAGS
89              where  FLAGS is a comma separated list of one or more flags out‐
90              lined below.  These flags are  associated  with  IFILE  and  are
91              ignored when IFILE is stdin.
92
93       obs=BS if given must be the same as BS given to 'bs=' option.
94
95       of=OFILE
96              write to OFILE instead of stdout. If OFILE is '-' then writes to
97              stdout. If OFILE is /dev/null then no  actual  writes  are  per‐
98              formed.   If  OFILE  is '.' (period) then it is treated the same
99              way as /dev/null (this is a shorthand notation). If OFILE exists
100              then  it is _not_ truncated; it is overwritten from the start of
101              OFILE unless 'oflag=append' or SEEK is given.
102
103       oflag=FLAGS
104              where FLAGS is a comma separated list of one or more flags  out‐
105              lined  below.   These  flags  are  associated with OFILE and are
106              ignored when OFILE is /dev/null, '.' (period), or stdout.
107
108       seek=SEEK
109              start writing SEEK bs-sized blocks  from  the  start  of  OFILE.
110              Default is block 0 (i.e. start of file).
111
112       skip=SKIP
113              start  reading  SKIP  bs-sized  blocks  from the start of IFILE.
114              Default is block 0 (i.e. start of file).
115
116       sync=0 | 1
117              when 1, does SYNCHRONIZE CACHE command on OFILE at  the  end  of
118              the transfer. Only active when OFILE is a sg device file name.
119
120       time=0 | 1
121              when  1,  times  transfer  and does throughput calculation, out‐
122              putting the results (to stderr) at completion. When 0  (default)
123              doesn't perform timing.
124
125       verbose=VERB
126              as  VERB  increases  so  does the amount of debug output sent to
127              stderr.  Default value is zero which yields the  minimum  amount
128              of debug output.  A value of 1 reports extra information that is
129              not repetitive. A value 2 reports cdbs and  responses  for  SCSI
130              commands  that  are  not  repetitive  (i.e.  other that READ and
131              WRITE). Error processing is not considered repetitive. Values of
132              3  and 4 yield output for all SCSI commands (and Unix read() and
133              write() calls) so there can be a lot of output.
134
135       -d, --dry-run
136              does all the command line parsing and preparation  but  bypasses
137              the  actual  copy  or read. That preparation may include opening
138              IFILE or OFILE to determine their lengths. This  option  may  be
139              useful  for  testing  the syntax of complex command line invoca‐
140              tions in advance of executing them.
141
142       -h, --help
143              outputs usage message and exits.
144
145       -v, --verbose
146              when used once, this is equivalent to verbose=1. When used twice
147              (e.g. "-vv") this is equivalent to verbose=2, etc.
148
149       -V, --version
150              outputs version number information and exits.
151

FLAGS

153       Here is a list of flags and their meanings:
154
155       append causes  the  O_APPEND flag to be added to the open of OFILE. For
156              normal files this will lead to data appended to the end  of  any
157              existing  data.   Cannot  be  used  together  with the seek=SEEK
158              option as they conflict.  The default action of this utility  is
159              to  overwrite  any  existing data from the beginning of the file
160              or, if SEEK is given, starting at block SEEK. Note that attempt‐
161              ing  to 'append' to a device file (e.g.  a disk) will usually be
162              ignored or may cause an error to be reported.
163
164       dio    is only active with oflag  (i.e.  'oflag=dio').  Its  action  is
165              described in the 'dio=1' option description above.
166
167       direct causes the O_DIRECT flag to be added to the open of IFILE and/or
168              OFILE. This flag requires some memory  alignment  on  IO.  Hence
169              user  memory buffers are aligned to the page size. Has no effect
170              on sg, normal or raw files.
171
172       dpo    set the DPO bit (disable page out) in SCSI READ and  WRITE  com‐
173              mands.  Not supported for 6 byte cdb variants of READ and WRITE.
174              Indicates that data is unlikely to be required to stay in device
175              (e.g.  disk)  cache.   May speed media copy and/or cause a media
176              copy to have less impact on other device users.
177
178       dsync  causes the O_SYNC flag to be added to the open of  IFILE  and/or
179              OFILE.  The  "d"  is  prepended  to  lower  confusion  with  the
180              'sync=0|1' option which has another action (i.e. a  synchronisa‐
181              tion to media at the end of the transfer).
182
183       excl   causes  the  O_EXCL flag to be added to the open of IFILE and/or
184              OFILE.
185
186       fua    causes the FUA (force unit access) bit to be set  in  SCSI  READ
187              and/or WRITE commands. This only has effect with sg devices. The
188              6 byte variants of the SCSI READ and WRITE commands do not  sup‐
189              port the FUA bit.  Only active for sg device file names.
190
191       null   has no affect, just a placeholder.
192

RETIRED OPTIONS

194       Here are some retired options that are still present:
195
196       fua=0 | 1 | 2 | 3
197              force  unit  access  bit.  When  3, fua is set on both IFILE and
198              OFILE; when 2, fua is set on IFILE; when 1, fua is set on OFILE;
199              when 0 (default), fua is cleared on both. See the 'fua' flag.
200

NOTES

202       A  raw  device  must  be bound to a block device prior to using sgm_dd.
203       See raw(8) for more information about binding raw devices. To be  safe,
204       the  sg device mapping to SCSI block devices should be checked with the
205       lsscsi utility before use.
206
207       Raw device partition information can often be found with fdisk(8)  [the
208       "-ul" argument is useful in this respect].
209
210       Various  numeric  arguments (e.g. SKIP) may include multiplicative suf‐
211       fixes or be given in hexadecimal. See the "NUMERIC  ARGUMENTS"  section
212       in the sg3_utils(8) man page.
213
214       The  count,  skip and seek parameters can take 64 bit values (i.e. very
215       big numbers). Other values are limited to what can fit in a  signed  32
216       bit number.
217
218       Data  usually  gets  to  the user space in a 2 stage process: first the
219       SCSI adapter DMAs into kernel buffers and then  the  sg  driver  copies
220       this  data  into  user memory (write operations reverse this sequence).
221       With memory mapped transfers a kernel buffer reserved by sg  is  memory
222       mapped  (see the mmap(2) system call) into the user space. When this is
223       done the second (redundant) copy from kernel buffers to user  space  is
224       not needed. Hence the transfer is faster and requires less "grunt" from
225       the CPU.
226
227       All informative, warning and error output is sent  to  stderr  so  that
228       dd's output file can be stdout and remain unpolluted. If no options are
229       given, then the usage message is output and nothing else happens.
230
231       For sg devices this utility issues SCSI READ and WRITE  (SBC)  commands
232       which  are  appropriate  for  disks  and reading from CD/DVD/BD drives.
233       Those commands are not formatted correctly for tape devices  so  sgm_dd
234       should not be used on tape devices.
235
236       This  utility  stops  the  copy  if  any error is encountered. For more
237       advanced "copy on error" logic see the sg_dd  utility  (and  its  'coe'
238       flag).
239

EXAMPLES

241       See the examples given in the man page for sg_dd(8).
242

SIGNALS

244       The signal handling has been borrowed from dd: SIGINT, SIGQUIT and SIG‐
245       PIPE output the number of remaining blocks to be  transferred  and  the
246       records  in + out counts; then they have their default action.  SIGUSR1
247       causes the same information to be output yet the copy  continues.   All
248       output caused by signals is sent to stderr.
249

EXIT STATUS

251       The exit status of sgm_dd is 0 when it is successful. Otherwise see the
252       sg3_utils(8) man page. Since this utility works at a higher level  than
253       individual  commands, and there are 'coe' and 'retries' flags, individ‐
254       ual SCSI command failures do not necessary cause the process to exit.
255

AUTHORS

257       Written by Douglas Gilbert and Peter Allworth.
258

REPORTING BUGS

260       Report bugs to <dgilbert at interlog dot com>.
261
263       Copyright © 2000-2018 Douglas Gilbert
264       This software is distributed under the GPL version 2. There is NO  war‐
265       ranty;  not  even  for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
266       POSE.
267

SEE ALSO

269       The simplest variant of this utility is called sg_dd.  A POSIX  threads
270       version  of this utility called sgp_dd is in the sg3_utils package. The
271       lmbench package  contains  lmdd  which  is  also  interesting.   dd(1),
272       ddpt(ddpt), raw(8)
273
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276sg3_utils-1.43                     June 2018                         SGM_DD(8)
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