1SGM_DD(8) SG3_UTILS SGM_DD(8)
2
6 sgm_dd - copy data to and from files and devices, especially SCSI
7 devices
8
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 [bpt=BPT] [cdbsz=6|10|12|16] [dio=0|1] [sync=0|1] [time=0|1] [ver‐
14 bose=VERB]
15
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 Will only perform memory mapped transfers when IFILE or OFILE are SCSI
23 generic (sg) devices.
24 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 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
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 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 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 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 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 ibs=BS if given must be the same as BS given to 'bs=' option.
82 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 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 obs=BS if given must be the same as BS given to 'bs=' option.
94 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 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 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 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 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 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 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 --help outputs usage message and exits.
136 --version
138 outputs version number information and exits.
139
141 Here is a list of flags and their meanings:
142 append causes the O_APPEND flag to be added to the open of OFILE. For
144 normal files this will lead to data appended to the end of any
145 existing data. Cannot be used together with the seek=SEEK
146 option as they conflict. The default action of this utility is
147 to overwrite any existing data from the beginning of the file
148 or, if SEEK is given, starting at block SEEK. Note that attempt‐
149 ing to 'append' to a device file (e.g. a disk) will usually be
150 ignored or may cause an error to be reported.
151 dio is only active with oflag (i.e. 'oflag=dio'). Its action is
153 described in the 'dio=1' option description above.
154 direct causes the O_DIRECT flag to be added to the open of IFILE and/or
156 OFILE. This flag requires some memory alignment on IO. Hence
157 user memory buffers are aligned to the page size. Has no effect
158 on sg, normal or raw files.
159 dpo set the DPO bit (disable page out) in SCSI READ and WRITE com‐
161 mands. Not supported for 6 byte cdb variants of READ and WRITE.
162 Indicates that data is unlikely to be required to stay in device
163 (e.g. disk) cache. May speed media copy and/or cause a media
164 copy to have less impact on other device users.
165 dsync causes the O_SYNC flag to be added to the open of IFILE and/or
167 OFILE. The "d" is prepended to lower confusion with the
168 'sync=0|1' option which has another action (i.e. a synchronisa‐
169 tion to media at the end of the transfer).
170 excl causes the O_EXCL flag to be added to the open of IFILE and/or
172 OFILE.
173 fua causes the FUA (force unit access) bit to be set in SCSI READ
175 and/or WRITE commands. This only has effect with sg devices. The
176 6 byte variants of the SCSI READ and WRITE commands do not sup‐
177 port the FUA bit. Only active for sg device file names.
178 null has no affect, just a placeholder.
180
182 Here are some retired options that are still present:
183 fua=0 | 1 | 2 | 3
185 force unit access bit. When 3, fua is set on both IFILE and
186 OFILE; when 2, fua is set on IFILE; when 1, fua is set on OFILE;
187 when 0 (default), fua is cleared on both. See the 'fua' flag.
188
190 A raw device must be bound to a block device prior to using sgm_dd.
191 See raw(8) for more information about binding raw devices. To be safe,
192 the sg device mapping to SCSI block devices should be checked with the
193 lsscsi utility before use.
194 Raw device partition information can often be found with fdisk(8) [the
196 "-ul" argument is useful in this respect].
197 Various numeric arguments (e.g. SKIP) may include multiplicative suf‐
199 fixes or be given in hexadecimal. See the "NUMERIC ARGUMENTS" section
200 in the sg3_utils(8) man page.
201 The count, skip and seek parameters can take 64 bit values (i.e. very
203 big numbers). Other values are limited to what can fit in a signed 32
204 bit number.
205 Data usually gets to the user space in a 2 stage process: first the
207 SCSI adapter DMAs into kernel buffers and then the sg driver copies
208 this data into user memory (write operations reverse this sequence).
209 With memory mapped transfers a kernel buffer reserved by sg is memory
210 mapped (see the mmap(2) system call) into the user space. When this is
211 done the second (redundant) copy from kernel buffers to user space is
212 not needed. Hence the transfer is faster and requires less "grunt" from
213 the CPU.
214 All informative, warning and error output is sent to stderr so that
216 dd's output file can be stdout and remain unpolluted. If no options are
217 given, then the usage message is output and nothing else happens.
218 For sg devices this utility issues SCSI READ and WRITE (SBC) commands
220 which are appropriate for disks and reading from CD/DVD/BD drives.
221 Those commands are not formatted correctly for tape devices so sgm_dd
222 should not be used on tape devices.
223 This utility stops the copy if any error is encountered. For more
225 advanced "copy on error" logic see the sg_dd utility (and its 'coe'
226 flag).
227
229 See the examples given in the man page for sg_dd(8).
230
232 The signal handling has been borrowed from dd: SIGINT, SIGQUIT and SIG‐
233 PIPE output the number of remaining blocks to be transferred and the
234 records in + out counts; then they have their default action. SIGUSR1
235 causes the same information to be output yet the copy continues. All
236 output caused by signals is sent to stderr.
237
239 The exit status of sgm_dd is 0 when it is successful. Otherwise see the
240 sg3_utils(8) man page. Since this utility works at a higher level than
241 individual commands, and there are 'coe' and 'retries' flags, individ‐
242 ual SCSI command failures do not necessary cause the process to exit.
243
245 Written by Douglas Gilbert and Peter Allworth.
246
248 Report bugs to <dgilbert at interlog dot com>.
249
251 Copyright © 2000-2015 Douglas Gilbert
252 This software is distributed under the GPL version 2. There is NO war‐
253 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
254 POSE.
255
257 The simplest variant of this utility is called sg_dd. A POSIX threads
258 version of this utility called sgp_dd is in the sg3_utils package. The
259 lmbench package contains lmdd which is also interesting. dd(1),
260 ddpt(ddpt), raw(8)
261sg3_utils-1.41 February 2015 SGM_DD(8)