NAME

       sg_readcap - send SCSI READ CAPACITY command

SYNOPSIS

       sg_readcap   [--16]   [--brief]  [--help]  [--hex]  [--lba=LBA]  [--long]  [--pmi]  [--raw]  [--readonly]
       [--verbose] [--version] DEVICE

       sg_readcap [-16] [-b] [-h] [-H] [-lba=LBA] [-pmi] [-r] [-R] [-v] [-V] DEVICE

DESCRIPTION

       The normal action of the SCSI READ CAPACITY command is to fetch the number of  blocks  (and  block  size)
       from the DEVICE.

       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.

       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.

       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).

       If sg_readcap is called without the --long option then the 10 byte cdb version (i.e. READ CAPACITY  (10))
       is  sent  to the DEVICE. If the number of blocks in the response is reported as 0xffffffff (i.e. (2**32 -
       1) ) and the --hex option has not been given, then READ CAPACITY (16)  is  called  and  its  response  is
       output.

       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.

OPTIONS

       Arguments to long options are mandatory for short options as well.

       --16   Use  the  16  byte cdb variant of the READ CAPACITY command. See the '--long' option.  -b, --brief
              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.

       -h, --help
              print out the usage message then exit.

       -H, --hex
              output  the  response to the READ CAPACITY command (either the 10 or 16 byte cdb variant) in ASCII
              hexadecimal on stdout.

       -L, --lba=LBA
              used in conjunction with --pmi option. This variant of READ CAPACITY will  yield  the  last  block
              address  after  LBA prior to a delay. For a disk, given a LBA it yields the highest numbered block
              on the same cylinder (i.e. before the heads need to move). LBA 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.

       -l, --long
              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).

       -O, --old
              switch to older style options.

       -p, --pmi
              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 --lba=LBA option. This option was  made  obsolete
              in SBC-3 revision 26.

       -r, --raw
              output response in binary to stdout.

       -R, --readonly
              open  the  DEVICE  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.

       -v, --verbose
              increase level of verbosity. Can be used multiple times.

       -V, --version
              outputs version string then exits.

NOTES

       In the 2.4 series of Linux kernels the DEVICE 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.

EXIT STATUS

       The exit status of sg_readcap is 0 when it is successful. Otherwise see the sg3_utils(8) man page.

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.

       -16    Use the 16 byte cdb variant of the READ CAPACITY  command.   Equivalent  to  --long  in  the  main
              description.

       -b     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 --brief in the main description.

       -h     output the usage message then exit. Giving the -? option  also  outputs  the  usage  message  then
              exits.

       -H     output  the  response to the READ CAPACITY command (either the 10 or 16 byte cdb variant) in ASCII
              hexadecimal on stdout.

       -lba=LBA
              used in conjunction with -pmi option. This variant of READ CAPACITY  will  yield  the  last  block
              address after LBA prior to a delay.  Equivalent to --lba=LBA in the main description.

       -N     switch to the newer style options.

       -pmi   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 --pmi in the main description.

       -r     output response in binary (to stdout).

       -R     Equivalent to --readonly in the main description.

       -v     verbose:  print  out cdb of issued commands prior to execution. '-vv' and '-vvv' are also accepted
              yielding greater verbosity.

       -V     outputs version string then exits.

AUTHORS

       Written by Douglas Gilbert

COPYRIGHT

       Copyright © 1999-2014 Douglas Gilbert
       This software is distributed under the GPL version 2. There is NO warranty; not even for  MERCHANTABILITY
       or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO

       sg_inq(sg3_utils)

sg3_utils-1.39                                      May 2014                                       SG_READCAP(8)