1SG_READCAP(8) SG3_UTILS SG_READCAP(8)
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6 sg_readcap - send SCSI READ CAPACITY command
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9 sg_readcap [--16] [--brief] [--help] [--hex] [--lba=LBA] [--long]
10 [--pmi] [--raw] [--readonly] [--verbose] [--version] DEVICE
11 sg_readcap [-16] [-b] [-h] [-H] [-lba=LBA] [-pmi] [-r] [-R] [-v] [-V]
13 DEVICE
14
16 The normal action of the SCSI READ CAPACITY command is to fetch the
17 number of blocks (and block size) from the DEVICE.
18 The SCSI READ CAPACITY command (both 10 and 16 byte cdbs) actually
20 yield the block address of the last block and the block size. The num‐
21 ber of blocks is thus one plus the block address of the last block (as
22 blocks are counted origin zero (i.e. starting at block zero)). This is
23 the source of many "off by one" errors.
24 The READ CAPACITY(16) response provides additional information not
26 found in the READ CAPACITY(10) response. This includes protection and
27 logical block provisioning information, plus the number of logical
28 blocks per physical block. So even though the media size may not exceed
29 what READ CAPACITY(10) can show, it may still be useful to examine the
30 response to READ CAPACITY(16). Sadly there are horrible SCSI command
31 set implementations in the wild that crash when the READ CAPACITY(16)
32 command is sent to them.
33 Device capacity is the product of the number of blocks by the block
35 size. This utility outputs this figure in bytes, MiB (1048576 bytes
36 per MiB) and GB (1000000000 bytes per GB).
37 If sg_readcap is called without the --long option then the 10 byte cdb
39 version (i.e. READ CAPACITY (10)) is sent to the DEVICE. If the number
40 of blocks in the response is reported as 0xffffffff (i.e. (2**32 - 1) )
41 and the --hex option has not been given, then READ CAPACITY (16) is
42 called and its response is output.
43 This utility supports two command line syntaxes, the preferred one is
45 shown first in the synopsis and explained in this section. A later sec‐
46 tion on the old command line syntax outlines the second group of
47 options.
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50 Arguments to long options are mandatory for short options as well.
51 --16 Use the 16 byte cdb variant of the READ CAPACITY command.
54 See the '--long' option. -b, --brief outputs two hex
55 numbers (prefixed with '0x' and space separated) to std‐
56 out. The first number is the maximum number of blocks on
57 the device (which is one plus the lba of the last acces‐
58 sible block). The second number is the size in bytes of
59 each block. If the operation fails then "0x0 0x0" is
60 written to stdout.
61 -h, --help
63 print out the usage message then exit.
64 -H, --hex
66 output the response to the READ CAPACITY command (either
67 the 10 or 16 byte cdb variant) in ASCII hexadecimal on
68 stdout.
69 -L, --lba=LBA
71 used in conjunction with --pmi option. This variant of
72 READ CAPACITY will yield the last block address after LBA
73 prior to a delay. For a disk, given a LBA it yields the
74 highest numbered block on the same cylinder (i.e. before
75 the heads need to move). LBA is assumed to be decimal
76 unless prefixed by "0x" or it has a trailing "h".
77 Defaults to 0. This option was made obsolete in SBC-3
78 revision 26.
79 -l, --long
81 Use the 16 byte cdb variant of the READ CAPACITY command.
82 The default action is to use the 10 byte cdb variant
83 which limits the maximum block address to (2**32 - 2).
84 When a 10 byte cdb READ CAPACITY command is used on a
85 device whose size is too large then a last block address
86 of 0xffffffff is returned (if the device complies with
87 SBC-2 or later).
88 -O, --old
90 switch to older style options.
91 -p, --pmi
93 partial medium indicator: for finding the next block
94 address prior to some delay (e.g. head movement). In the
95 absence of this option, the total number of blocks and
96 the block size of the device are output. Used in con‐
97 junction with the --lba=LBA option. This option was made
98 obsolete in SBC-3 revision 26.
99 -r, --raw
101 output response in binary to stdout.
102 -R, --readonly
104 open the DEVICE read-only (e.g. in Unix with the O_RDONLY
105 flag). The default for READ CAPACITY(16) is to open it
106 read-write. The default for READ CAPACITY(10) is to open
107 it read-only so this option does not change anything for
108 this case.
109 -v, --verbose
111 increase level of verbosity. Can be used multiple times.
112 -V, --version
114 outputs version string then exits.
115
117 In the 2.4 series of Linux kernels the DEVICE must be a SCSI
118 generic (sg) device. In the 2.6 series block devices (e.g. SCSI
119 disks and DVD drives) can also be specified. For example
120 "sg_readcap /dev/sda" and "sg_readcap /dev/hdd" (if /dev/hdd is
121 a ATAPI CD/DVD device) will work in the 2.6 series kernels.
122
124 The exit status of sg_readcap is 0 when it is successful. Other‐
125 wise see the sg3_utils(8) man page.
126
128 The options in this section were the only ones available prior
129 to sg3_utils version 1.23 . In sg3_utils version 1.23 and later
130 these older options can be selected by either setting the
131 SG3_UTILS_OLD_OPTS environment variable or using '--old' (or
132 '-O) as the first option.
133 -16 Use the 16 byte cdb variant of the READ CAPACITY command.
135 Equivalent to --long in the main description.
136 -b utility outputs two hex numbers (prefixed with '0x' and
138 space separated) to stdout. The first number is the maxi‐
139 mum number of blocks on the device (which is one plus the
140 lba of the last accessible block). The second number is
141 the size of each block. If the operation fails then "0x0
142 0x0" is written to stdout. Equivalent to --brief in the
143 main description.
144 -h output the usage message then exit. Giving the -? option
146 also outputs the usage message then exits.
147 -H output the response to the READ CAPACITY command (either
149 the 10 or 16 byte cdb variant) in ASCII hexadecimal on
150 stdout.
151 -lba=LBA
153 used in conjunction with -pmi option. This variant of
154 READ CAPACITY will yield the last block address after LBA
155 prior to a delay. Equivalent to --lba=LBA in the main
156 description.
157 -N switch to the newer style options.
159 -pmi partial medium indicator: for finding the next block
161 address prior to some delay (e.g. head movement). In the
162 absence of this switch, the total number of blocks and
163 the block size of the device are output. Equivalent to
164 --pmi in the main description.
165 -r output response in binary (to stdout).
167 -R Equivalent to --readonly in the main description.
169 -v verbose: print out cdb of issued commands prior to execu‐
171 tion. '-vv' and '-vvv' are also accepted yielding greater
172 verbosity.
173 -V outputs version string then exits.
175
177 Written by Douglas Gilbert
178
180 Copyright © 1999-2014 Douglas Gilbert
181 This software is distributed under the GPL version 2. There is
182 NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PAR‐
183 TICULAR PURPOSE.
184
186 sg_inq(sg3_utils)
187sg3_utils-1.39 May 2014 SG_READCAP(8)