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] [--verbose] [--version] DEVICE
11 sg_readcap [-16] [-b] [-h] [-H] [-lba=LBA] [-pmi] [-r] [-v] [-V] DEVICE
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15 The normal action of the SCSI READ CAPACITY command is to fetch the
16 number of blocks (and block size) from the DEVICE.
17 The SCSI READ CAPACITY command (both 10 and 16 byte cdbs) actually
19 yield the block address of the last block and the block size. The num‐
20 ber of blocks is thus one plus the block address of the last block (as
21 blocks are counted origin zero (i.e. starting at block zero)). This is
22 the source of many "off by one" errors.
23 The READ CAPACITY(16) response provides additional information not
25 found in the READ CAPACITY(10) response. This includes protection and
26 logical block provisioning information, plus the number of logical
27 blocks per physical block. So even though the media size may not exceed
28 what READ CAPACITY(10) can show, it may still be useful to examine the
29 response to READ CAPACITY(16). Sadly there are horrible SCSI command
30 set implementations in the wild that crash when the READ CAPACITY(16)
31 command is sent to them.
32 Device capacity is the product of the number of blocks by the block
34 size. This utility outputs this figure in bytes, MiB (1048576 bytes
35 per MiB) and GB (1000000000 bytes per GB).
36 If sg_readcap is called without the --long option then the 10 byte cdb
38 version (i.e. READ CAPACITY (10)) is sent to the DEVICE. If the number
39 of blocks in the response is reported as 0xffffffff (i.e. (2**32 - 1) )
40 and the --hex option has not been given, then READ CAPACITY (16) is
41 called and its response is output.
42 This utility supports two command line syntaxes, the preferred one is
44 shown first in the synopsis and explained in this section. A later sec‐
45 tion on the old command line syntax outlines the second group of
46 options.
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49 Arguments to long options are mandatory for short options as well.
50 --16 Use the 16 byte cdb variant of the READ CAPACITY command.
53 See the '--long' option. -b, --brief outputs two hex
54 numbers (prefixed with '0x' and space separated) to std‐
55 out. The first number is the maximum number of blocks on
56 the device (which is one plus the lba of the last acces‐
57 sible block). The second number is the size in bytes of
58 each block. If the operation fails then "0x0 0x0" is
59 written to stdout.
60 -h, --help
62 print out the usage message then exit.
63 -H, --hex
65 output the response to the READ CAPACITY command (either
66 the 10 or 16 byte cdb variant) in ASCII hexadecimal on
67 stdout.
68 -L, --lba=LBA
70 used in conjunction with --pmi option. This variant of
71 READ CAPACITY will yield the last block address after LBA
72 prior to a delay. For a disk, given a LBA it yields the
73 highest numbered block on the same cylinder (i.e. before
74 the heads need to move). LBA is assumed to be decimal
75 unless prefixed by "0x" or it has a trailing "h".
76 Defaults to 0. This option was made obsolete in SBC-3
77 revision 26.
78 -l, --long
80 Use the 16 byte cdb variant of the READ CAPACITY command.
81 The default action is to use the 10 byte cdb variant
82 which limits the maximum block address to (2**32 - 2).
83 When a 10 byte cdb READ CAPACITY command is used on a
84 device whose size is too large then a last block address
85 of 0xffffffff is returned (if the device complies with
86 SBC-2 or later).
87 -O, --old
89 Switch to older style options. Please use as first
90 option.
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 -v, --verbose
104 increase level of verbosity. Can be used multiple times.
105 -V, --version
107 outputs version string then exits.
108
110 In the 2.4 series of Linux kernels the DEVICE must be a SCSI
111 generic (sg) device. In the 2.6 series block devices (e.g. SCSI
112 disks and DVD drives) can also be specified. For example
113 "sg_readcap /dev/sda" and "sg_readcap /dev/hdd" (if /dev/hdd is
114 a ATAPI CD/DVD device) will work in the 2.6 series kernels.
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117 The exit status of sg_readcap is 0 when it is successful. Other‐
118 wise see the sg3_utils(8) man page.
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121 The options in this section were the only ones available prior
122 to sg3_utils version 1.23 . In sg3_utils version 1.23 and later
123 these older options can be selected by either setting the
124 SG3_UTILS_OLD_OPTS environment variable or using '--old' (or
125 '-O) as the first option.
126 -16 Use the 16 byte cdb variant of the READ CAPACITY command.
128 Equivalent to --long in the main description.
129 -b utility outputs two hex numbers (prefixed with '0x' and
131 space separated) to stdout. The first number is the maxi‐
132 mum number of blocks on the device (which is one plus the
133 lba of the last accessible block). The second number is
134 the size of each block. If the operation fails then "0x0
135 0x0" is written to stdout. Equivalent to --brief in the
136 main description.
137 -h output the usage message then exit. Giving the -? option
139 also outputs the usage message then exits.
140 -H output the response to the READ CAPACITY command (either
142 the 10 or 16 byte cdb variant) in ASCII hexadecimal on
143 stdout.
144 -lba=LBA
146 used in conjunction with -pmi option. This variant of
147 READ CAPACITY will yield the last block address after LBA
148 prior to a delay. Equivalent to --lba=LBA in the main
149 description.
150 -N, --new
152 Switch to the newer style options.
153 -pmi partial medium indicator: for finding the next block
155 address prior to some delay (e.g. head movement). In the
156 absence of this switch, the total number of blocks and
157 the block size of the device are output. Equivalent to
158 --pmi in the main description.
159 -r output response in binary (to stdout).
161 -v verbose: print out cdb of issued commands prior to execu‐
163 tion. '-vv' and '-vvv' are also accepted yielding greater
164 verbosity.
165 -V outputs version string then exits.
167
169 Written by Douglas Gilbert
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172 Copyright © 1999-2013 Douglas Gilbert
173 This software is distributed under the GPL version 2. There is
174 NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PAR‐
175 TICULAR PURPOSE.
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178 sg_inq(sg3_utils)
179sg3_utils-1.36 May 2012 SG_READCAP(8)