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SG_REQUESTS(8) SG3_UTILS SG_REQUESTS(8)
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 sup-
ported.
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 ille-
gal 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 imple-
mented 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 "al-
location 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 sta-
tus) 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 EX-
CEEDED 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 opera-
tions 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 pro-
cessing 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 de-
vice returns to its normal state.
The SCSI FORMAT command for disks used with the IMMED bit set is an example of an opera-
tion 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 as-
sociated 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 (C) 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.
SEE ALSO
sg_turs (sg3_utils)
sg3_utils-1.45 July 2018 SG_REQUESTS(8)
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