1SGM_DD(8) SG3_UTILS SGM_DD(8)
2
6 sgm_dd - copies data to and from files and devices. Specialized for
7 devices that understand the SCSI command set and does memory mapped
8 transfers from sg devices.
9
11 sgm_dd [bs=BS] [count=COUNT] [ibs=BS] [if=IFILE] [iflag=FLAGS] [obs=BS]
12 [of=OFILE] [oflag=FLAGS] [seek=SEEK] [skip=SKIP] [--help] [--version]
13 [bpt=BPT] [cdbsz=6|10|12|16] [dio=0|1] [sync=0|1] [time=0|1] [ver‐
15 bose=VERB]
16
18 Copy data to and from any files. Specialized for "files" that are Linux
19 SCSI generic (sg) devices and raw devices. Uses memory mapped transfers
20 on sg devices. Similar syntax and semantics to dd(1) but does not per‐
21 form any conversions.
22 Will only perform memory mapped transfers when IFILE or OFILE are SCSI
24 generic (sg) devices. If both IFILE and OFILE are sg devices then mem‐
25 ory mapped transfers are only performed on IFILE.
26 The first group in the synopsis above are "standard" Unix dd(1) oper‐
28 ands. The second group are extra options added by this utility. Both
29 groups are defined below.
30
32 bpt=BPT
33 each IO transaction will be made using BPT blocks (or less if
34 near the end of the copy). Default is 128 for block sizes less
35 that 2048 bytes, otherwise the default is 32. So for bs=512 the
36 reads and writes will each convey 64 KiB of data by default
37 (less if near the end of the transfer or memory restrictions).
38 When cd/dvd drives are accessed, the block size is typically
39 2048 bytes and bpt defaults to 32 which again implies 64 KiB
40 transfers.
41 bs=BS where BS must be the block size of the physical device. Note
43 that this differs from dd(1) which permits BS to be an integral
44 multiple. Default is 512 which is usually correct for disks but
45 incorrect for cdroms (which normally have 2048 byte blocks). For
46 this utility the maximum size of each individual IO operation is
47 BS * BPT bytes.
48 cdbsz=6 | 10 | 12 | 16
50 size of SCSI READ and/or WRITE commands issued on sg device
51 names. Default is 10 byte SCSI command blocks (unless calcula‐
52 tions indicate that a 4 byte block number may be exceeded, in
53 which case it defaults to 16 byte SCSI commands).
54 count=COUNT
56 copy COUNT blocks from IFILE to OFILE. Default is the minimum
57 (of IFILE and OFILE) number of blocks that sg devices report
58 from SCSI READ CAPACITY commands or that block devices (or their
59 partitions) report. Normal files are not probed for their size.
60 If skip=SKIP or skip=SEEK are given and the count is derived
61 (i.e. not explicitly given) then the derived count is scaled
62 back so that the copy will not overrun the device. If the file
63 name is a block device partition and COUNT is not given then the
64 size of the partition rather than the size of the whole device
65 is used. If COUNT is not given and cannot be derived then an
66 error message is issued and no copy takes place.
67 dio=0 | 1
69 permits direct IO to be selected on the write-side (i.e. on
70 OFILE). Only allowed when the read-side (i.e. IFILE) is a sg
71 device. When 1 there may be a "zero copy" copy (i.e. mmap-ed
72 transfer on the read into the user space and direct IO from
73 there on the write, potentially two DMAs and no data copying
74 from the CPU). Default is 0.
75 ibs=BS if given must be the same as BS given to 'bs=' option.
77 if=IFILE
79 read from IFILE instead of stdin. If IFILE is '-' then stdin is
80 read. Starts reading at the beginning of IFILE unless SKIP is
81 given.
82 iflag=FLAGS
84 where FLAGS is a comma separated list of one or more flags out‐
85 lined below. These flags are associated with IFILE and are
86 ignored when IFILE is stdin.
87 obs=BS if given must be the same as BS given to 'bs=' option.
89 of=OFILE
91 write to OFILE instead of stdout. If OFILE is '-' then writes to
92 stdout. If OFILE is /dev/null then no actual writes are per‐
93 formed. If OFILE is '.' (period) then it is treated the same
94 way as /dev/null (this is a shorthand notation). If OFILE exists
95 then it is _not_ truncated; it is overwritten from the start of
96 OFILE unless 'oflag=append' or SEEK is given.
97 oflag=FLAGS
99 where FLAGS is a comma separated list of one or more flags out‐
100 lined below. These flags are associated with OFILE and are
101 ignored when OFILE is /dev/null, '.' (period), or stdout.
102 seek=SEEK
104 start writing SEEK bs-sized blocks from the start of OFILE.
105 Default is block 0 (i.e. start of file).
106 skip=SKIP
108 start reading SKIP bs-sized blocks from the start of IFILE.
109 Default is block 0 (i.e. start of file).
110 sync=0 | 1
112 when 1, does SYNCHRONIZE CACHE command on OFILE at the end of
113 the transfer. Only active when OFILE is a sg device file name.
114 time=0 | 1
116 when 1, times transfer and does throughput calculation, out‐
117 putting the results (to stderr) at completion. When 0 (default)
118 doesn't perform timing.
119 verbose=VERB
121 as VERB increases so does the amount of debug output sent to
122 stderr. Default value is zero which yields the minimum amount
123 of debug output. A value of 1 reports extra information that is
124 not repetitive. A value 2 reports cdbs and responses for SCSI
125 commands that are not repetitive (i.e. other that READ and
126 WRITE). Error processing is not considered repetitive. Values of
127 3 and 4 yield output for all SCSI commands (and Unix read() and
128 write() calls) so there can be a lot of output.
129 --help outputs usage message and exits.
131 --version
133 outputs version number information and exits.
134
136 Here is a list of flags and their meanings:
137 append causes the O_APPEND flag to be added to the open of OFILE. For
139 normal files this will lead to data appended to the end of any
140 existing data. Cannot be used together with the seek=SEEK
141 option as they conflict. The default action of this utility is
142 to overwrite any existing data from the beginning of the file
143 or, if SEEK is given, starting at block SEEK. Note that attempt‐
144 ing to 'append' to a device file (e.g. a disk) will usually be
145 ignored or may cause an error to be reported.
146 direct causes the O_DIRECT flag to be added to the open of IFILE and/or
148 OFILE. This flag requires some memory alignment on IO. Hence
149 user memory buffers are aligned to the page size. Has no effect
150 on sg, normal or raw files.
151 dpo set the DPO bit (disable page out) in SCSI READ and WRITE com‐
153 mands. Not supported for 6 byte cdb variants of READ and WRITE.
154 Indicates that data is unlikely to be required to stay in device
155 (e.g. disk) cache. May speed media copy and/or cause a media
156 copy to have less impact on other device users.
157 dsync causes the O_SYNC flag to be added to the open of IFILE and/or
159 OFILE. The "d" is prepended to lower confusion with the
160 'sync=0|1' option which has another action (i.e. a synchronisa‐
161 tion to media at the end of the transfer).
162 excl causes the O_EXCL flag to be added to the open of IFILE and/or
164 OFILE.
165 fua causes the FUA (force unit access) bit to be set in SCSI READ
167 and/or WRITE commands. This only has effect with sg devices. The
168 6 byte variants of the SCSI READ and WRITE commands do not sup‐
169 port the FUA bit. Only active for sg device file names.
170
172 Here are some retired options that are still present:
173 fua=0 | 1 | 2 | 3
175 force unit access bit. When 3, fua is set on both IFILE and
176 OFILE; when 2, fua is set on IFILE; when 1, fua is set on OFILE;
177 when 0 (default), fua is cleared on both. See the 'fua' flag.
178
180 A raw device must be bound to a block device prior to using sgm_dd.
181 See raw(8) for more information about binding raw devices. To be safe,
182 the sg device mapping to SCSI block devices should be checked with 'cat
183 /proc/scsi/scsi' before use.
184 Raw device partition information can often be found with fdisk(8) [the
186 "-ul" argument is useful in this respect].
187 COUNT, SKIP, SEEK, BPT and BS may include one of these multiplicative
189 suffixes: c C *1; w W *2; b B *512; k K KiB *1,024; KB *1,000; m M MiB
190 *1,048,576; MB *1,000,000 . This pattern continues for "G", "T" and
191 "P". The latter two suffixes can only be used for COUNT, SKIP and SEEK.
192 Also a suffix of the form "x<n>" multiplies the leading number by <n>.
193 These multiplicative suffixes are compatible with GNU's dd command
194 (since 2002) which claims compliance with SI and with IEC 60027-2.
195 Alternatively numerical values can be given in hexadecimal preceded by
197 either "0x" or "0X" (or with a trailing "h" or "H"). When hex numbers
198 are given, multipliers cannot be used.
199 The count, skip and seek parameters can take 64 bit values (i.e. very
201 big numbers). Other values are limited to what can fit in a signed 32
202 bit number.
203 Data usually gets to the user space in a 2 stage process: first the
205 SCSI adapter DMAs into kernel buffers and then the sg driver copies
206 this data into user memory (write operations reverse this sequence).
207 With memory mapped transfers a kernel buffer reserved by sg is memory
208 mapped (see the mmap(2) system call) into the user space. When this is
209 done the second (redundant) copy from kernel buffers to user space is
210 not needed. Hence the transfer is faster and requires less "grunt" from
211 the CPU.
212 All informative, warning and error output is sent to stderr so that
214 dd's output file can be stdout and remain unpolluted. If no options are
215 given, then the usage message is output and nothing else happens.
216 For sg devices this utility issues SCSI READ and WRITE (SBC) commands
218 which are appropriate for disks and reading from CD/DVD drives. Those
219 commands are not formatted correctly for tape devices so sgm_dd should
220 not be used on tape devices.
221 This utility stops the copy if any error is encountered. For more
223 advanced "copy on error" logic see the sg_dd utility (and its 'coe'
224 flag).
225
227 See the examples given in the man page for sg_dd(8).
228
230 The signal handling has been borrowed from dd: SIGINT, SIGQUIT and SIG‐
231 PIPE output the number of remaining blocks to be transferred and the
232 records in + out counts; then they have their default action. SIGUSR1
233 causes the same information to be output yet the copy continues. All
234 output caused by signals is sent to stderr.
235
237 The exit status of sgm_dd is 0 when it is successful. Otherwise see the
238 sg3_utils(8) man page. Since this utility works at a higher level than
239 individual commands, and there are 'coe' and 'retries' flags, individ‐
240 ual SCSI command failures do not necessary cause the process to exit.
241
243 Written by Doug Gilbert and Peter Allworth.
244
246 Report bugs to <dgilbert at interlog dot com>.
247
249 Copyright © 2000-2007 Douglas Gilbert
250 This software is distributed under the GPL version 2. There is NO war‐
251 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
252 POSE.
253
255 The simplest variant of this utility is called sg_dd. A POSIX threads
256 version of this utility called sgp_dd is in the sg3_utils package. The
257 lmbench package contains lmdd which is also interesting. raw(8), dd(1)
258sg3_utils-1.23 January 2007 SGM_DD(8)