sg_requests (8)

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

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.

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.

-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 .

-p, --progress

show progress indication (a percentage) if available. If --number=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.

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. More recent standards seem to suggest 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).

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

Written by Douglas Gilbert.

Report bugs to <dgilbert at interlog dot com>.

Copyright © 2004-2014 Douglas Gilbert

This software is distributed under a FreeBSD license. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

sg3_utils