sg3_utils - a package of utilities for sending SCSI commands


sg_* [--help] [--hex] [--maxlen=LEN] [--raw] [--verbose] [--version] [OTHER_OPTIONS] DEVICE


sg3_utils is a package of utilities that send SCSI commands to the given DEVICE via a SCSI pass through interface provided by the host operating system.

The names of all utilities start with "sg" and most start with "sg_" often followed by the name, or a shortening of the name, of the SCSI command that they send. For example the "sg_verify" utility sends the SCSI VERIFY command. A mapping between SCSI commands and the sg3_utils utilities that issue them is shown in the COVERAGE file.

SCSI draft standards can be found at . The standards themselves can be purchased from ANSI and other standards organizations. A good overview of various SCSI standards can be seen in with the SCSI command sets in the upper part of the diagram. SCSI commands in common with all device types can be found in SPC of which SPC-4 is the latest major version. Block device specific commands (e.g. as used by disks) are in SBC, those for tape drives in SSC and those for CD/DVD/HD_DVD/BD drives in MMC.

There are two generations of command line option usage. The newer utilities (written since July 2004) use the getopt_long() function to parse command line options. With that function, each option has two representations: a short form (e.g. ’-v’) and a longer form (e.g. ’--verbose’). If an argument is required then it follows a space (optionally) in the short form and a "=" in the longer form (e.g. in the sg_verify utility ’-l 2a6h’ and ’--lba=2a6h’ are equivalent). Note that with getopt_long(), short form options can be elided, for example: ’-all’ is equivalent to ’-a -l -l’. The DEVICE argument may appear after, between or prior to any options.

The older utilities, such as sg_inq, had individual command line processing code (often found at the top of the main() function) based on a single "-" followed by one or more characters. If an argument is needed then it follows a "=" (e.g. ’-p=1f’ in sg_modes with its older interface). Various options can be elided as long as it is not ambiguous (e.g. ’-vv’ to increase the verbosity).

Over time the command line interface of these older utilities became messy and overloaded with options. So in sg3_utils version 1.23 the command line interface of these older utilities was altered to have both a cleaner getopt_long() interface and their older interface for backward compatibility. By default these older utilities use their getopt_long() based interface. That can be overridden by defining the SG3_UTILS_OLD_OPTS environment variable or using ’-O’ or ’--old’ as the first command line option. The man pages of the older utilities documents the details.

Several sg3_utils utilities are based on the Unix dd command (e.g. sg_dd) and share dd’s rather quirky command line interface.


To aid scripts that call these utilities, the exit status is set to indicate success (0) or failure (1 or more). Note that some of the lower values correspond to the SCSI sense key values. The exit status values are:
0 success
1 syntax error. Either illegal command line options, options with bad arguments or a combination of options that is not permitted.
2 the DEVICE reports that it is not ready for the operation requested. The device may be in the process of becoming ready (e.g. spinning up but not at speed) so the utility may work after a wait.
3 the DEVICE reports a medium or hardware error (or a blank check). For example an attempt to read a corrupted block on a disk will yield this value.
5 the DEVICE reports an "illegal request" with an additional sense code other than "invalid command operation code". This is often a supported command with a field set requesting an unsupported capability. For commands that require a "service action" field this value can indicate that the command with that service action value is not supported.
6 the DEVICE reports a "unit attention" condition. This usually indicates that something unrelated to the requested command has occurred (e.g. a device reset) potentially before the current SCSI command was sent. The requested command has not been executed by the device. Note that unit attention conditions are usually only reported once by a device.
9 the DEVICE reports an illegal request with an additional sense code of "invalid command operation code" which means that it doesn’t support the requested command.
11 the DEVICE reports an aborted command. In some cases aborted commands can be retried immediately (e.g. if the transport aborted the command due to congestion).
15 the utility is unable to open, close or use the given DEVICE. The given file name could be incorrect or there may be permission problems. Adding the ’-v’ option may give more information.
20 the DEVICE reports it has a check condition but "no sense" and non-zero information in its additional sense codes. Some polling commands (e.g. REQUEST SENSE) can receive this response.
21 the DEVICE reports a "recovered error". The requested command was successful. Most likely a utility will report a recovered error to stderr and continue, probably leaving the utility with an exit status of 0 .
33 the command sent to DEVICE has timed out.
97 the response to a SCSI command failed sanity checks.
98 the DEVICE reports it has a check condition but the error doesn’t fit into any of the above categories.
99 any errors that can’t be categorized into values 1 to 98 may yield this value. This includes transport and operating system errors after the command has been sent to the device.
Most of the error conditions reported above will be repeatable (an example of one that is not is "unit attention") so the utility can be run again with the ’-v’ option (or several) to obtain more information.


Arguments to long options are mandatory for short options as well. In the short form an argument to an option uses zero or more spaces as a separator (i.e. the short form does not use "=" as a separator).

If an option takes a numeric argument then that argument is assumed to be decimal unless otherwise indicated (e.g. with a leading "0x", a trailing "h" or as noted in the usage message).
-h, -?, --help
 output the usage message then exit. In a few older utilities the ’-h’ option requests hexadecimal output. In these cases the ’-?’ option will output the usage message then exit.
-H, --hex for SCSI commands that yield a non-trivial response, print out that response in ASCII hexadecimal.
-m, --maxlen=LEN
 several important SCSI commands (e.g. INQUIRY and MODE SENSE) have response lengths that vary depending on many factors, only some of which these utilities take into account. The maximum response length is typically specified in the ’allocation length’ field of the cdb. In the absence of this option, several utilities use a default allocation length (sometimes recommended in the SCSI draft standards) or a "double fetch" strategy. See sg_logs(8) for its description of a "double fetch" strategy. These techniques are imperfect and in the presence of faulty SCSI targets can cause problems (e.g. some USB mass storage devices freeze if they receive an INQUIRY allocation length other than 36). Also use of this option disables any "double fetch" strategy that may have otherwise been used.
-r, --raw for SCSI commands that yield a non-trivial response, output that response in binary to stdout. If any error messages or warning are produced they are usually sent to stderr. Some utilities that consume data to send to the device along with the SCSI command, use this option to provide that data or indicate that it can be read from stdin.
-v, --verbose
 increase the level of verbosity, (i.e. debug output). Can be used multiple times to further increase verbosity. The additional output is usually sent to stderr.
-V, --version
 print the version string and then exit. Each utility has its own version number and date of last code change.


Written by Douglas Gilbert.


Report bugs to <dgilbert at interlog dot com>.


Copyright © 1999-2008 Douglas Gilbert Some utilities are distributed under a GPL version 2 license while others, usually more recent ones, are under a FreeBSD license. The files that are common to almost all utilities and thus contain the most reusable code, namely sg_lib.[hc], sg_cmds_basic.[hc] and sg_cmds_extra.[hc] are under a FreeBSD license. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.



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