Ubuntu Manpage: sg_requests - send one or more SCSI REQUEST SENSE commands

Provided by: sg3-utils_1.46-3ubuntu2.1_amd64

NAME

       sg_requests - send one or more SCSI REQUEST SENSE commands

SYNOPSIS

       sg_requests  [--desc] [--error] [--help] [--hex] [--maxlen=LEN] [--num=NUM] [--number=NUM]
       [--progress] [--raw] [--status] [--time] [--verbose] [--version] DEVICE

DESCRIPTION

       Send SCSI REQUEST SENSE command to DEVICE and output the parameter data response which  is
       expected  to  be  in  sense  data format. Both fixed and descriptor sense data formats are
       supported.

       Multiple REQUEST SENSE commands can be sent with the --num=NUM option. This  can  be  used
       for timing purposes or monitoring the progress indication.

OPTIONS

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

-d, --desc
sets the DESC bit in the REQUEST SENSE SCSI cdb. The DEVICE should return sense
data in descriptor (rather than fixed) format. This will only occur if the DEVICE
recognizes descriptor format (SPC-3 and later). If the device is pre SPC-3 then
setting a bit in a reserved field may cause a check condition status with an
illegal request sense key, but will most likely be ignored.

-e, --error
when used once it changes the REQUEST SENSE opcode from 0x3 to 0xff which should be
rejected by the DEVICE. There is a small chance that the device vendor has
implemented a vendor specific command at that opcode (0xff). When used twice the
pass-through call to send the SCSI command is bypassed. The idea here is to
measure the user space overhead of this package's library to set up and process the
response of a SCSI command. This option will be typically used with the --num=NUM
and --time options where NUM is a large number (e.g. 1000000).

-h, --help
output the usage message then exit.

-H, --hex
output response in ASCII hexadecimal.

-m, --maxlen=LEN
where LEN is the (maximum) response length in bytes. It is placed in the cdb's
"allocation length" field. If not given (or LEN is zero) then 252 is used. The
maximum value of LEN is 255 (but SPC-4 recommends 252).

-n, --num=NUM
perform NUM SCSI REQUEST SENSE commands, stopping when either NUM is reached or an
error occurs. The default value for NUM is 1 .

--number=NUM
same action as --num=NUM. Added for compatibility with sg_turs.

-p, --progress
show progress indication (a percentage) if available. If --num=NUM is given, NUM is
greater than 1 and an initial progress indication was detected then this utility
waits 30 seconds before subsequent checks. Exits when NUM is reached or there are
no more progress indications. Ignores --hex, --raw and --time options. See NOTES
section below.

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

-s, --status
if the REQUEST SENSE command finished without error (as indicated by its SCSI
status) then the contents of the parameter data are analysed as sense data and the
exit status is set accordingly. The default action (i.e. when this option is not
given) is to ignore the contents of the parameter data for the purposes of setting
the exit status. Some types of error set a sense key of "NO SENSE" with non-zero
information in the additional sense code (e.g. the FAILURE PREDICTION THRESHOLD
EXCEEDED group of codes); this results in an exit status value of 10. If the sense
key is "NO SENSE" and both asc and ascq are zero then the exit status is set to 0 .
See the sg3_utils(8) man page for exit status values.

-t, --time
time the SCSI REQUEST SENSE command(s) and calculate the average number of
operations per second.

-v, --verbose
increase the level of verbosity, (i.e. debug output). Additionally the response
(if received) is output in ASCII-HEX. Use this option multiple times for greater
verbosity.

-V, --version
print the version string and then exit.

NOTES

In SCSI 1 and 2 the REQUEST SENSE command was very important for error and warning
processing in SCSI. The autosense capability rendered this command almost superfluous.

However recent SCSI drafts (e.g. SPC-4 rev 14 and SBC-3 rev 14) increase the utility of
the REQUEST SENSE command. Idle and standby (low) power conditions can be detected with
this command.

The REQUEST SENSE command is not marked as mandatory in SPC-3 (i.e. for all SCSI devices)
but is marked as mandatory in SBC-2 (i.e. for disks), SSC-3 (i.e. for tapes) and MMC-4
(i.e. for CD/DVD/HD-DVD/BD drives).

The progress indication is optionally part of the sense data. When a prior command that
takes a long time to complete (and typically precludes other media access commands) is
still underway, the progress indication can be used to determine how long before the
device returns to its normal state.

The SCSI FORMAT command for disks used with the IMMED bit set is an example of an
operation that takes a significant amount of time and precludes other media access during
that time. The IMMED bit set instructs the FORMAT command to return control to the
application client once the format has commenced (see SBC-3). Several long duration SCSI
commands associated with tape drives also use the progress indication (see SSC-3).

Early standards suggested that the SCSI TEST UNIT READY command be used for polling the
progress indication (see the sg_turs utility). Since SPC-3 the standards suggest that the
SCSI REQUEST SENSE command should be used instead.

The DEVICE is opened with a read-only flag (e.g. in Unix with the O_RDONLY flag).

EXIT STATUS

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

AUTHORS

       Written by Douglas Gilbert.

REPORTING BUGS

       Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT

       Copyright © 2004-2017 Douglas Gilbert
       This software is distributed under a FreeBSD license. There is NO warranty; not  even  for
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.