1SG_READCAP(8) SG3_UTILS SG_READCAP(8)
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6 sg_readcap - sends a SCSI READ CAPACITY command
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9 sg_readcap [--brief] [--help] [--hex] [--lba=LBA] [--long] [--pmi]
10 [--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 Device capacity is the product of the number of blocks by the block
25 size. This utility outputs this figure in bytes, MiB (1048576 bytes
26 per MiB) and GB (1000000000 bytes per GB).
27 This utility supports two command line syntaxes, the preferred one is
29 shown first in the synopsis and explained in this section. A later sec‐
30 tion on the old command line syntax outlines the second group of
31 options.
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34 Arguments to long options are mandatory for short options as well.
35 -b, --brief
37 outputs two hex numbers (prefixed with '0x' and space separated)
38 to stdout. The first number is the maximum number of blocks on
39 the device (which is one plus the lba of the last accessible
40 block). The second number is the size of each block. If the
41 operation fails then "0x0 0x0" is written to stdout.
42 -h, --help
44 print out the usage message then exit.
45 -H, --hex
47 output the response to the READ CAPACITY command (either the 10
48 or 16 byte cdb variant) in ASCII hexadecimal on stdout.
49 -L, --lba=LBA
51 used in conjunction with --pmi option. This variant of READ
52 CAPACITY will yield the last block address after LBA prior to a
53 delay. For a disk, given a LBA it yields the highest numbered
54 block on the same cylinder (i.e. before the heads need to move).
55 LBA is assumed to be decimal unless prefixed by "0x" or it has a
56 trailing "h". Defaults to 0.
57 -l, --long
59 Use the 16 byte cdb variant of the READ CAPACITY command. The
60 default action is to use the 10 byte cdb variant which limits
61 the maximum block address to (2**32 - 2). When a 10 byte cdb
62 READ CAPACITY command is used on a device whose size is too
63 large then a last block address of 0xffffffff is returned (if
64 the device complies with SBC-2).
65 -O, --old
67 switch to older style options.
68 -p, --pmi
70 partial medium indicator: for finding the next block address
71 prior to some delay (e.g. head movement). In the absence of this
72 option, the total number of blocks and the block size of the
73 device are output. Used in conjunction with the --lba=LBA
74 option.
75 -r, --raw
77 output response in binary to stdout.
78 -v, --verbose
80 increase level of verbosity. Can be used multiple times.
81 -V, --version
83 outputs version string then exits.
84
86 If sg_readcap is called without the --long option then the 10 byte cdb
87 version (i.e. READ CAPACITY (10)) is sent to the DEVICE. If the number
88 of blocks in the response is reported as 0xffffffff (i.e. (2**32 - 1) )
89 and the --hex option has not been given, then READ CAPACITY (16) is
90 called and its response is output.
91 The read capacity(16) response shows additional information not found
93 in the read capacity(10) response. This includes protection information
94 and the number of logical blocks per physical block. So even though the
95 media size may not exceed what READ CAPACITY(10) can show, it may still
96 be useful to examine the response to READ CAPACITY(16).
97 In the 2.4 series of Linux kernels the DEVICE must be a SCSI generic
99 (sg) device. In the 2.6 series block devices (e.g. SCSI disks and DVD
100 drives) can also be specified. For example "sg_readcap /dev/sda" and
101 "sg_readcap /dev/hdd" (if /dev/hdd is a ATAPI CD/DVD device) will work
102 in the 2.6 series kernels.
103
105 The exit status of sg_readcap is 0 when it is successful. Otherwise see
106 the sg3_utils(8) man page.
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109 The options in this section were the only ones available prior to
110 sg3_utils version 1.23 . In sg3_utils version 1.23 and later these
111 older options can be selected by either setting the SG3_UTILS_OLD_OPTS
112 environment variable or using '--old' (or '-O) as the first option.
113 -16 Use the 16 byte cdb variant of the READ CAPACITY command.
115 Equivalent to --long in the main description.
116 -b utility outputs two hex numbers (prefixed with '0x' and space
118 separated) to stdout. The first number is the maximum number of
119 blocks on the device (which is one plus the lba of the last
120 accessible block). The second number is the size of each block.
121 If the operation fails then "0x0 0x0" is written to stdout.
122 Equivalent to --brief in the main description.
123 -h output the usage message then exit. Giving the -? option also
125 outputs the usage message then exits.
126 -H output the response to the READ CAPACITY command (either the 10
128 or 16 byte cdb variant) in ASCII hexadecimal on stdout.
129 -lba=LBA
131 used in conjunction with -pmi option. This variant of READ
132 CAPACITY will yield the last block address after LBA prior to a
133 delay. Equivalent to --lba=LBA in the main description.
134 -N switch to the newer style options.
136 -pmi partial medium indicator: for finding the next block address
138 prior to some delay (e.g. head movement). In the absence of this
139 switch, the total number of blocks and the block size of the
140 device are output. Equivalent to --pmi in the main description.
141 -r output response in binary (to stdout).
143 -v verbose: print out cdb of issued commands prior to execution.
145 '-vv' and '-vvv' are also accepted yielding greater verbosity.
146 -V outputs version string then exits.
148
150 Written by Douglas Gilbert
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153 Copyright © 1999-2007 Douglas Gilbert
154 This software is distributed under the GPL version 2. There is NO war‐
155 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
156 POSE.
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159 sg_inq(sg3_utils)
160sg3_utils-1.23 January 2007 SG_READCAP(8)