.TH SG_READCAP "8" "May 2014" "sg3_utils\-1.39" SG3_UTILS
.SH NAME
sg_readcap \- send SCSI READ CAPACITY command
.SH SYNOPSIS
.B sg_readcap
[\fI\-\-16\fR] [\fI\-\-brief\fR] [\fI\-\-help\fR] [\fI\-\-hex\fR]
[\fI\-\-lba=LBA\fR] [\fI\-\-long\fR] [\fI\-\-pmi\fR] [\fI\-\-raw\fR]
[\fI\-\-readonly\fR] [\fI\-\-verbose\fR] [\fI\-\-version\fR] \fIDEVICE\fR
.PP
.B sg_readcap
[\fI\-16\fR] [\fI\-b\fR] [\fI\-h\fR] [\fI\-H\fR] [\fI\-lba=LBA\fR]
[\fI\-pmi\fR] [\fI\-r\fR] [\fI\-R\fR] [\fI\-v\fR] [\fI\-V\fR] \fIDEVICE\fR
.SH DESCRIPTION
.\" Add any additional description here
.PP
The normal action of the SCSI READ CAPACITY command is to fetch the number
of blocks (and block size) from the \fIDEVICE\fR.
.PP
The SCSI READ CAPACITY command (both 10 and 16 byte cdbs) actually yield
the block address of the last block and the block size. The number of
blocks is thus one plus the block address of the last block (as blocks
are counted origin zero (i.e. starting at block zero)). This is the source
of many "off by one" errors.
.PP
The READ CAPACITY(16) response provides additional information not found in
the READ CAPACITY(10) response. This includes protection and logical block
provisioning information, plus the number of logical blocks per physical
block. So even though the media size may not exceed what READ CAPACITY(10)
can show, it may still be useful to examine the response to READ
CAPACITY(16). Sadly there are horrible SCSI command set implementations in
the wild that crash when the READ CAPACITY(16) command is sent to them.
.PP
Device capacity is the product of the number of blocks by the block size.
This utility outputs this figure in bytes, MiB (1048576 bytes per MiB)
and GB (1000000000 bytes per GB).
.PP
If sg_readcap is called without the \fI\-\-long\fR option then the 10 byte
cdb version (i.e. READ CAPACITY (10)) is sent to the \fIDEVICE\fR. If the
number of blocks in the response is reported as
0xffffffff (i.e. (2**32 \- 1) ) and the \fI\-\-hex\fR option has not been
given, then READ CAPACITY (16) is called and its response is output.
.PP
This utility supports two command line syntaxes, the preferred one is
shown first in the synopsis and explained in this section. A later section
on the old command line syntax outlines the second group of options.
.SH OPTIONS
Arguments to long options are mandatory for short options as well.
.TP
.TP
\fB\-\-16\fR
Use the 16 byte cdb variant of the READ CAPACITY command. See the '\-\-long'
option.
\fB\-b\fR, \fB\-\-brief\fR
outputs two hex numbers (prefixed with '0x' and space separated)
to stdout. The first number is the maximum number of blocks on the
device (which is one plus the lba of the last accessible block). The
second number is the size in bytes of each block. If the operation fails
then "0x0 0x0" is written to stdout.
.TP
\fB\-h\fR, \fB\-\-help\fR
print out the usage message then exit.
.TP
\fB\-H\fR, \fB\-\-hex\fR
output the response to the READ CAPACITY command (either the 10 or 16
byte cdb variant) in ASCII hexadecimal on stdout.
.TP
\fB\-L\fR, \fB\-\-lba\fR=\fILBA\fR
used in conjunction with \fI\-\-pmi\fR option. This variant of READ CAPACITY
will yield the last block address after \fILBA\fR prior to a delay. For a
disk, given a \fILBA\fR it yields the highest numbered block on the same
cylinder (i.e. before the heads need to move). \fILBA\fR is assumed to be
decimal unless prefixed by "0x" or it has a trailing "h". Defaults to 0.
This option was made obsolete in SBC\-3 revision 26.
.TP
\fB\-l\fR, \fB\-\-long\fR
Use the 16 byte cdb variant of the READ CAPACITY command. The default
action is to use the 10 byte cdb variant which limits the maximum
block address to (2**32 \- 2). When a 10 byte cdb READ CAPACITY command
is used on a device whose size is too large then a last block address
of 0xffffffff is returned (if the device complies with SBC\-2 or later).
.TP
\fB\-O\fR, \fB\-\-old\fR
switch to older style options.
.TP
\fB\-p\fR, \fB\-\-pmi\fR
partial medium indicator: for finding the next block address prior to
some delay (e.g. head movement). In the absence of this option, the
total number of blocks and the block size of the device are output.
Used in conjunction with the \fI\-\-lba=LBA\fR option. This option was
made obsolete in SBC\-3 revision 26.
.TP
\fB\-r\fR, \fB\-\-raw\fR
output response in binary to stdout.
.TP
\fB\-R\fR, \fB\-\-readonly\fR
open the \fIDEVICE\fR read\-only (e.g. in Unix with the O_RDONLY flag).
The default for READ CAPACITY(16) is to open it read\-write. The default
for READ CAPACITY(10) is to open it read\-only so this option does not
change anything for this case.
.TP
\fB\-v\fR, \fB\-\-verbose\fR
increase level of verbosity. Can be used multiple times.
.TP
\fB\-V\fR, \fB\-\-version\fR
outputs version string then exits.
.SH NOTES
In the 2.4 series of Linux kernels the \fIDEVICE\fR must be a SCSI
generic (sg) device. In the 2.6 series block devices (e.g. SCSI disks
and DVD drives) can also be specified. For example "sg_readcap /dev/sda"
and "sg_readcap /dev/hdd" (if /dev/hdd is a ATAPI CD/DVD device) will
work in the 2.6 series kernels.
.SH EXIT STATUS
The exit status of sg_readcap is 0 when it is successful. Otherwise see
the sg3_utils(8) man page.
.SH OLDER COMMAND LINE OPTIONS
The options in this section were the only ones available prior to sg3_utils
version 1.23 . In sg3_utils version 1.23 and later these older options can
be selected by either setting the SG3_UTILS_OLD_OPTS environment variable
or using '\-\-old' (or '\-O) as the first option.
.TP
\fB\-16\fR
Use the 16 byte cdb variant of the READ CAPACITY command.
Equivalent to \fI\-\-long\fR in the main description.
.TP
\fB\-b\fR
utility outputs two hex numbers (prefixed with '0x' and space separated) to
stdout. The first number is the maximum number of blocks on the device (which
is one plus the lba of the last accessible block). The second number is the
size of each block. If the operation fails then "0x0 0x0" is written to
stdout.  Equivalent to \fI\-\-brief\fR in the main description.
.TP
\fB\-h\fR
output the usage message then exit. Giving the \fI\-?\fR option also outputs
the usage message then exits.
.TP
\fB\-H\fR
output the response to the READ CAPACITY command (either the 10 or 16
byte cdb variant) in ASCII hexadecimal on stdout.
.TP
\fB\-lba\fR=\fILBA\fR
used in conjunction with \fI\-pmi\fR option. This variant of READ CAPACITY
will yield the last block address after \fILBA\fR prior to a delay.
Equivalent to \fI\-\-lba=LBA\fR in the main description.
.TP
\fB\-N\fR
switch to the newer style options.
.TP
\fB\-pmi\fR
partial medium indicator: for finding the next block address prior to
some delay (e.g. head movement). In the absence of this switch, the
total number of blocks and the block size of the device are output.
Equivalent to \fI\-\-pmi\fR in the main description.
.TP
\fB\-r\fR
output response in binary (to stdout).
.TP
\fB\-R\fR
Equivalent to \fI\-\-readonly\fR in the main description.
.TP
\fB\-v\fR
verbose: print out cdb of issued commands prior to execution. '\-vv'
and '\-vvv' are also accepted yielding greater verbosity.
.TP
\fB\-V\fR
outputs version string then exits.
.SH AUTHORS
Written by Douglas Gilbert
.SH COPYRIGHT
Copyright \(co 1999\-2014 Douglas Gilbert
.br
This software is distributed under the GPL version 2. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
.SH "SEE ALSO"
.B sg_inq(sg3_utils)