1SG_DD(8) SG3_UTILS SG_DD(8)
2
6 sg_dd - copy data to and from files and devices, especially SCSI
7 devices
8
10 sg_dd [bs=BS] [conv=CONV] [count=COUNT] [ibs=BS] [if=IFILE]
11 [iflag=FLAGS] [obs=BS] [of=OFILE] [oflag=FLAGS] [seek=SEEK] [skip=SKIP]
12 [--help] [--version]
13 [blk_sgio={0|1}] [bpt=BPT] [cdbsz={6|10|12|16}] [coe={0|1|2|3}]
15 [coe_limit=CL] [dio={0|1}] [odir={0|1}] [of2=OFILE2] [retries=RETR]
16 [sync={0|1}] [time={0|1}] [verbose=VERB] [-V]
17
19 Copy data to and from any files. Specialized for "files" that are Linux
20 SCSI generic (sg) devices, raw devices or other devices that support
21 the SG_IO ioctl (which are only found in the lk 2.6 series). Similar
22 syntax and semantics to dd(1) command.
23 The first group in the synopsis above are "standard" Unix dd(1) oper‐
25 ands. The second group are extra options added by this utility. Both
26 groups are defined below.
27 This utility is only supported on Linux whereas most other utilities in
29 the sg3_utils package have been ported to other operating systems. A
30 utility called "ddpt" has similar syntax and functionality to sg_dd.
31 ddpt drops some Linux specific features while adding some other generic
32 features. This allows ddpt to be ported to other operating systems.
33
35 blk_sgio={0|1}
36 when set to 0, block devices (e.g. /dev/sda) are treated like
37 normal files (i.e. read(2) and write(2) are used for IO). When
38 set to 1, block devices are assumed to accept the SG_IO ioctl
39 and SCSI commands are issued for IO. This is only supported for
40 2.6 series kernels. Note that ATAPI devices (e.g. cd/dvd play‐
41 ers) use the SCSI command set but ATA disks do not (unless there
42 is a protocol conversion as often occurs in the USB mass storage
43 class). If the input or output device is a block device parti‐
44 tion (e.g. /dev/sda3) then setting this option causes the parti‐
45 tion information to be ignored (since access is directly to the
46 underlying device). Default is 0. See the 'sgio' flag.
47 bpt=BPT
49 each IO transaction will be made using BPT blocks (or less if
50 near the end of the copy). Default is 128 for block sizes less
51 that 2048 bytes, otherwise the default is 32. So for bs=512 the
52 reads and writes will each convey 64 KiB of data by default
53 (less if near the end of the transfer or memory restrictions).
54 When cd/dvd drives are accessed, the block size is typically
55 2048 bytes and bpt defaults to 32 which again implies 64 KiB
56 transfers. The block layer when the blk_sgio=1 option is used
57 has relatively low upper limits for transfer sizes (compared to
58 sg device nodes, see /sys/block/<dev_name>/queue/max_sectors_kb
59 ).
60 bs=BS where BS must be the block size of the physical device (if
62 either the input or output files are accessed via SCSI com‐
63 mands). Note that this differs from dd(1) which permits BS to be
64 an integral multiple. Default is 512 which is usually correct
65 for disks but incorrect for cdroms (which normally have 2048
66 byte blocks). For this utility the maximum size of each individ‐
67 ual IO operation is BS * BPT bytes.
68 cdbsz={6|10|12|16}
70 size of SCSI READ and/or WRITE commands issued on sg device
71 names (or block devices when 'iflag=sgio' and/or 'oflag=sgio' is
72 given). Default is 10 byte SCSI command blocks (unless calcula‐
73 tions indicate that a 4 byte block number may be exceeded or BPT
74 is greater than 16 bits (65535), in which case it defaults to 16
75 byte SCSI commands).
76 coe={0|1|2|3}
78 set to 1 or more for continue on error. Only applies to errors
79 on sg devices or block devices with the 'sgio' flag set. Thus
80 errors on other files will stop sg_dd. Default is 0 which
81 implies stop on any error. See the 'coe' flag for more informa‐
82 tion.
83 coe_limit=CL
85 where CL is the maximum number of consecutive bad blocks stepped
86 over (due to "coe>0") on reads before the copy terminates. This
87 only applies when IFILE is accessed via the SG_IO ioctl. The
88 default is 0 which is interpreted as no limit. This option is
89 meant to stop the copy soon after unrecorded media is detected
90 while still offering "continue on error" capability.
91 conv=sparse
93 see the CONVERSIONS section below.
94 count=COUNT
96 copy COUNT blocks from IFILE to OFILE. Default is the minimum
97 (of IFILE and OFILE) number of blocks that sg devices report
98 from SCSI READ CAPACITY commands or that block devices (or their
99 partitions) report. Normal files are not probed for their size.
100 If skip=SKIP or skip=SEEK are given and the count is derived
101 (i.e. not explicitly given) then the derived count is scaled
102 back so that the copy will not overrun the device. If the file
103 name is a block device partition and COUNT is not given then the
104 size of the partition rather than the size of the whole device
105 is used. If COUNT is not given (or count=-1) and cannot be
106 derived then an error message is issued and no copy takes place.
107 dio={0|1}
109 default is 0 which selects indirect (buffered) IO on sg devices.
110 Value of 1 attempts direct IO which, if not available, falls
111 back to indirect IO and notes this at completion. If direct IO
112 is selected and /proc/scsi/sg/allow_dio has the value of 0 then
113 a warning is issued (and indirect IO is performed). For finer
114 grain control use 'iflag=dio' or 'oflag=dio'.
115 ibs=BS if given must be the same as BS given to 'bs=' option.
117 if=IFILE
119 read from IFILE instead of stdin. If IFILE is '-' then stdin is
120 read. Starts reading at the beginning of IFILE unless SKIP is
121 given.
122 iflag=FLAGS
124 where FLAGS is a comma separated list of one or more flags out‐
125 lined below. These flags are associated with IFILE and are
126 ignored when IFILE is stdin.
127 obs=BS if given must be the same as BS given to 'bs=' option.
129 odir={0|1}
131 when set to one opens block devices (e.g. /dev/sda) with the
132 O_DIRECT flag. User memory buffers are aligned to the page size
133 when set. The default is 0 (i.e. the O_DIRECT flag is not used).
134 Has no effect on sg, normal or raw files. If blk_sgio is also
135 set then both are honoured: block devices are opened with the
136 O_DIRECT flag and SCSI commands are issued via the SG_IO ioctl.
137 of=OFILE
139 write to OFILE instead of stdout. If OFILE is '-' then writes to
140 stdout. If OFILE is /dev/null then no actual writes are per‐
141 formed. If OFILE is '.' (period) then it is treated the same
142 way as /dev/null (this is a shorthand notation). If OFILE exists
143 then it is _not_ truncated; it is overwritten from the start of
144 OFILE unless 'oflag=append' or SEEK is given.
145 of2=OFILE2
147 write output to OFILE2. The default action is not to do this
148 additional write (i.e. when this option is not given). OFILE2 is
149 assumed to be a normal file or a fifo (i.e. a named pipe).
150 OFILE2 is opened for writing, created if necessary, and closed
151 at the end of the transfer. If OFILE2 is a fifo (named pipe)
152 then some other command should be consuming that data (e.g.
153 'md5sum OFILE2'), otherwise this utility will block.
154 oflag=FLAGS
156 where FLAGS is a comma separated list of one or more flags out‐
157 lined below. These flags are associated with OFILE and are
158 ignored when OFILE is /dev/null, '.' (period), or stdout.
159 retries=RETR
161 sometimes retries at the host are useful, for example when there
162 is a transport error. When RETR is greater than zero then SCSI
163 READs and WRITEs are retried on error, RETR times. Default value
164 is zero.
165 seek=SEEK
167 start writing SEEK bs-sized blocks from the start of OFILE.
168 Default is block 0 (i.e. start of file).
169 skip=SKIP
171 start reading SKIP bs-sized blocks from the start of IFILE.
172 Default is block 0 (i.e. start of file).
173 sync={0|1}
175 when 1, does SYNCHRONIZE CACHE command on OFILE at the end of
176 the transfer. Only active when OFILE is a sg device file name or
177 a block device and 'blk_sgio=1' is given.
178 time={0|1}
180 when 1, times transfer and does throughput calculation, out‐
181 putting the results (to stderr) at completion. When 0 (default)
182 doesn't perform timing.
183 verbose=VERB
185 as VERB increases so does the amount of debug output sent to
186 stderr. Default value is zero which yields the minimum amount
187 of debug output. A value of 1 reports extra information that is
188 not repetitive. A value 2 reports cdbs and responses for SCSI
189 commands that are not repetitive (i.e. other that READ and
190 WRITE). Error processing is not considered repetitive. Values of
191 3 and 4 yield output for all SCSI commands (and Unix read() and
192 write() calls) so there can be a lot of output. This only
193 occurs for scsi generic (sg) devices and block devices when the
194 'blk_sgio=1' option is set.
195 --help outputs usage message and exits.
197 --version
199 outputs version number information and exits.
200 -V outputs version number information and exits.
202
204 One or more conversions can be given to the "conv=" option. If more
205 than one is given, they should be comma separated. sg_dd does not per‐
206 form the traditional dd conversions (e.g. ASCII to EBCDIC). Recently
207 added conversions overlap somewhat with the flags so some conversions
208 are now supported by sg_dd.
209 noerror
211 this conversion is very close to "iflag=coe" and is treated as
212 such. See the "coe" flag. Note that an error on OFILE will stop
213 the copy.
214 notrunc
216 this conversion is accepted for compatibilty with dd and ignored
217 since the default action of this utility is not to truncate
218 OFILE.
219 null has no affect, just a placeholder.
221 sparse FreeBSD supports "conv=sparse" so the same syntax is supported
223 in sg_dd. See "sparse" in the FLAGS sections for more informa‐
224 tion.
225 sync is ignored by sg_dd. With dd it means supply zero fill (rather
227 than skip) and is typically used like this "conv=noerror,sync"
228 to have the same functionality as sg_dd's "iflag=coe".
229
231 Here is a list of flags and their meanings:
232 append causes the O_APPEND flag to be added to the open of OFILE. For
234 regular files this will lead to data appended to the end of any
235 existing data. Cannot be used together with the seek=SEEK
236 option as they conflict. The default action of this utility is
237 to overwrite any existing data from the beginning of the file
238 or, if SEEK is given, starting at block SEEK. Note that attempt‐
239 ing to 'append' to a device file (e.g. a disk) will usually be
240 ignored or may cause an error to be reported.
241 coe continue on error. Only active for sg devices and block devices
243 that have the 'sgio' flag set. 'iflag=coe oflag=coe' and 'coe=1'
244 are equivalent. Use this flag twice (e.g. 'iflag=coe,coe') to
245 have the same action as the 'coe=2'. A medium, hardware or blank
246 check error while reading will re-read blocks prior to the bad
247 block, then try to recover the bad block, supplying zeros if
248 that fails, and finally reread the blocks after the bad block. A
249 medium, hardware or blank check error while writing is noted and
250 ignored. The recovery of the bad block when reading uses the
251 SCSI READ LONG command if 'coe' given twice or more (also with
252 the command line option 'coe=2'). Further, the READ LONG will
253 set its CORRCT bit if 'coe' given thrice. SCSI disks may auto‐
254 matically try and remap faulty sectors (see the AWRE and ARRE in
255 the read write error recovery mode page (the sdparm utility can
256 access and possibly change these attributes)). Errors occurring
257 on other files types will stop sg_dd. Error messages are sent
258 to stderr. This flag is similar
259 o 'conv=noerror,sync' in the dd(1) utility. See note about READ
260 LONG below.
261 dio request the sg device node associated with this flag does direct
263 IO. If direct IO is not available, falls back to indirect IO
264 and notes this at completion. If direct IO is selected and
265 /proc/scsi/sg/allow_dio has the value of 0 then a warning is
266 issued (and indirect IO is performed).
267 direct causes the O_DIRECT flag to be added to the open of IFILE and/or
269 OFILE. This flag requires some memory alignment on IO. Hence
270 user memory buffers are aligned to the page size. Has no effect
271 on sg, normal or raw files. If 'iflag=sgio' and/or 'oflag=sgio'
272 is also set then both are honoured: block devices are opened
273 with the O_DIRECT flag and SCSI commands are issued via the
274 SG_IO ioctl.
275 dpo set the DPO bit (disable page out) in SCSI READ and WRITE com‐
277 mands. Not supported for 6 byte cdb variants of READ and WRITE.
278 Indicates that data is unlikely to be required to stay in device
279 (e.g. disk) cache. May speed media copy and/or cause a media
280 copy to have less impact on other device users.
281 dsync causes the O_SYNC flag to be added to the open of IFILE and/or
283 OFILE. The 'd' is prepended to lower confusion with the
284 'sync=0|1' option which has another action (i.e. a synchronisa‐
285 tion to media at the end of the transfer).
286 excl causes the O_EXCL flag to be added to the open of IFILE and/or
288 OFILE.
289 flock after opening the associated file (i.e. IFILE and/or OFILE) an
291 attempt is made to get an advisory exclusive lock with the
292 flock() system call. The flock arguments are "FLOCK_EX |
293 FLOCK_NB" which will cause the lock to be taken if available
294 else a "temporarily unavailable" error is generated. An exit
295 status of 90 is produced in the latter case and no copy is done.
296 fua causes the FUA (force unit access) bit to be set in SCSI READ
298 and/or WRITE commands. This only has an effect with sg devices
299 or block devices that have the 'sgio' flag set. The 6 byte vari‐
300 ants of the SCSI READ and WRITE commands do not support the FUA
301 bit.
302 nocache
304 use posix_fadvise() to advise corresponding file there is no
305 need to fill the file buffer with recently read or written
306 blocks.
307 null has no affect, just a placeholder.
309 sgio causes block devices to be accessed via the SG_IO ioctl rather
311 than standard UNIX read() and write() commands. When the SG_IO
312 ioctl is used the SCSI READ and WRITE commands are used directly
313 to move data. sg devices always use the SG_IO ioctl. This flag
314 offers finer grain control compared to the otherwise identical
315 'blk_sgio=1' option.
316 sparse after each BS * BPT byte segment is read from the input, it is
318 checked for being all zeros. If so, nothing is written to the
319 output file unless this is the last segment of the transfer.
320 This flag is only active with the oflag option. It cannot be
321 used when the output is not seekable (e.g. stdout). It is
322 ignored if the output file is /dev/null . Note that this util‐
323 ity does not remove the OFILE prior to starting to write to it.
324 Hence it may be advantageous to manually remove the OFILE if it
325 is large prior to using oflag=sparse. The last segment is always
326 written so regular files will show the same length and so pro‐
327 grams like md5sum and sha1sum will generate the same value
328 regardless of whether oflag=sparse is given or not. This option
329 may be used when the OFILE is a raw device but is probably only
330 useful if the device is known to contain zeros (e.g. a SCSI disk
331 after a FORMAT command).
332
334 Here are some retired options that are still present:
335 append=0 | 1
337 when set, equivalent to 'oflag=append'. When clear the action is
338 to overwrite the existing file (if it exists); this is the
339 default. See the 'append' flag.
340 fua=0 | 1 | 2 | 3
342 force unit access bit. When 3, fua is set on both IFILE and
343 OFILE; when 2, fua is set on IFILE;, when 1, fua is set on
344 OFILE; when 0 (default), fua is cleared on both. See the 'fua'
345 flag.
346
348 Block devices (e.g. /dev/sda and /dev/hda) can be given for IFILE. If
349 neither '-iflag=direct', 'iflag=sgio' nor 'blk_sgio=1' is given then
350 normal block IO involving buffering and caching is performed. If only
351 '-iflag=direct' is given then the buffering and caching is bypassed
352 (this is applicable to both SCSI devices and ATA disks). If
353 'iflag=sgio' or 'blk_sgio=1' is given then the SG_IO ioctl is used on
354 the given file causing SCSI commands to be sent to the device and that
355 also bypasses most of the actions performed by the block layer (this is
356 only applicable to SCSI devices, not ATA disks). The same applies for
357 block devices given for OFILE.
358 Various numeric arguments (e.g. SKIP) may include multiplicative suf‐
360 fixes or be given in hexadecimal. See the "NUMERIC ARGUMENTS" section
361 in the sg3_utils(8) man page.
362 The COUNT, SKIP and SEEK arguments can take 64 bit values (i.e. very
364 big numbers). Other values are limited to what can fit in a signed 32
365 bit number.
366 Data usually gets to the user space in a 2 stage process: first the
368 SCSI adapter DMAs into kernel buffers and then the sg driver copies
369 this data into user memory (write operations reverse this sequence).
370 This is called "indirect IO" and there is a 'dio' option to select
371 "direct IO" which will DMA directly into user memory. Due to some
372 issues "direct IO" is disabled in the sg driver and needs a configura‐
373 tion change to activate it. This is typically done with 'echo 1 >
374 /proc/scsi/sg/allow_dio'.
375 All informative, warning and error output is sent to stderr so that
377 dd's output file can be stdout and remain unpolluted. If no options are
378 given, then the usage message is output and nothing else happens.
379 Even if READ LONG succeeds on a "bad" block when 'coe=2' (or 'coe=3')
381 is given, the recovered data may not be useful. There are no guarantees
382 that the user data will appear "as is" in the first 512 bytes.
383 A raw device must be bound to a block device prior to using sg_dd. See
385 raw(8) for more information about binding raw devices. To be safe, the
386 sg device mapping to SCSI block devices should be checked with 'cat
387 /proc/scsi/scsi', or sg_map before use.
388 Disk partition information can often be found with fdisk(8) [the "-ul"
390 argument is useful in this respect].
391 For sg devices (and block devices when blk_sgio=1 is given) this util‐
393 ity issues SCSI READ and WRITE (SBC) commands which are appropriate for
394 disks and reading from CD/DVD/HD-DVD/BD drives. Those commands are not
395 formatted correctly for tape devices so sg_dd should not be used on
396 tape devices. If the largest block address of the requested transfer
397 exceeds a 32 bit block number (i.e 0xffff) then a warning is issued and
398 the sg device is accessed via SCSI READ(16) and WRITE(16) commands.
399 The attributes of a block device (partition) are ignored when
401 'blk_sgio=1' is used. Hence the whole device is read (rather than just
402 the second partition) by this invocation:
403 sg_dd if=/dev/sdb2 blk_sgio=1 of=t bs=512
405
407 Looks quite similar in usage to dd:
408 sg_dd if=/dev/sg0 of=t bs=512 count=1MB
410 This will copy 1 million 512 byte blocks from the device associated
412 with /dev/sg0 (which should have 512 byte blocks) to a file called t.
413 Assuming /dev/sda and /dev/sg0 are the same device then the above is
414 equivalent to:
415 dd if=/dev/sda iflag=direct of=t bs=512 count=1000000
417 although dd's speed may improve if bs was larger and count was suitably
419 reduced. The use of the 'iflag=direct' option bypasses the buffering
420 and caching that is usually done on a block device.
421 Using a raw device to do something similar on a ATA disk:
423 raw /dev/raw/raw1 /dev/hda
425 sg_dd if=/dev/raw/raw1 of=t bs=512 count=1MB
426 To copy a SCSI disk partition to an ATA disk partition:
428 raw /dev/raw/raw2 /dev/hda3
430 sg_dd if=/dev/sg0 skip=10123456 of=/dev/raw/raw2 bs=512
431 This assumes a valid partition is found on the SCSI disk at the given
433 skip block address (past the 5 GB point of that disk) and that the par‐
434 tition goes to the end of the SCSI disk. An explicit count is probably
435 a safer option. The partition is copied to /dev/hda3 which is an offset
436 into the ATA disk /dev/hda . The exact number of blocks read from
437 /dev/sg0 are written to /dev/hda (i.e. no padding).
438 To time a streaming read of the first 1 GB (2 ** 30 bytes) on a disk
440 this utility could be used:
441 sg_dd if=/dev/sg0 of=/dev/null bs=512 count=2m time=1
443 On completion this will output a line like: "time to transfer data was
445 18.779506 secs, 57.18 MB/sec". The "MB/sec" in this case is 1,000,000
446 bytes per second.
447 The 'of2=' option can be used to copy data and take a md5sum of it
449 without needing to re-read the data:
450 mkfifo fif
452 md5sum fif &
453 sg_dd if=/dev/sg3 iflag=coe of=sg3.img oflag=sparse of2=fif bs=512
454 This will image /dev/sg3 (e.g. an unmounted disk) and place the con‐
456 tents in the (sparse) file sg3.img . Without re-reading the data it
457 will also perform a md5sum calculation on the image.
458
460 The signal handling has been borrowed from dd: SIGINT, SIGQUIT and SIG‐
461 PIPE output the number of remaining blocks to be transferred and the
462 records in + out counts; then they have their default action. SIGUSR1
463 causes the same information to be output yet the copy continues. All
464 output caused by signals is sent to stderr.
465
467 The exit status of sg_dd is 0 when it is successful. Otherwise see the
468 sg3_utils(8) man page. Since this utility works at a higher level than
469 individual commands, and there are 'coe' and 'retries' flags, individ‐
470 ual SCSI command failures do not necessary cause the process to exit.
471 An additional exit status of 90 is generated if the flock flag is given
473 and some other process holds the advisory exclusive lock.
474
476 Written by Douglas Gilbert and Peter Allworth.
477
479 Report bugs to <dgilbert at interlog dot com>.
480
482 Copyright © 2000-2013 Douglas Gilbert
483 This software is distributed under the GPL version 2. There is NO war‐
484 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
485 POSE.
486
488 There is a web page discussing sg_dd at
489 http://sg.danny.cz/sg/sg_dd.html
490 A POSIX threads version of this utility called sgp_dd is in the
492 sg3_utils package. Another version from that package is called sgm_dd
493 and it uses memory mapped IO to speed transfers from sg devices.
494 The lmbench package contains lmdd which is also interesting. For moving
496 data to and from tapes see dt which is found at http://www.scsi‐
497 faq.org/RMiller_Tools/index.html
498 To change mode parameters that effect a SCSI device's caching and error
500 recovery see sdparm(sdparm)
501 To verify the data on the media or to verify it against some other copy
503 of the data see sg_verify(sg3_utils)
504 See also raw(8), dd(1), ddrescue(GNU), ddpt
506sg3_utils-1.37 June 2013 SG_DD(8)