sg3_utils - a package of utilities for sending SCSI commands
sg_* [--help] [--hex] [--maxlen=LEN] [--raw] [--verbose] [--version]
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
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 http://www.t10.org . The standards
themselves can be purchased from ANSI and other standards
organizations. A good overview of various SCSI standards can be seen
in http://www.t10.org/scsi-3.htm 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
It is becoming more common to control ATA disks with the SCSI command
set. This involves the translation of SCSI commands to their
corresponding ATA equivalents (and that is an imperfect mapping in some
cases). The relevant standard is called SCSI to ATA Translation (SAT
and SAT-2 are now standards at INCITS(ANSI) and ISO while SAT-3 is at
the draft stage). The logic to perform the command translation is often
called a SAT Layer or SATL and may be within an operating system, in
host bus adapter firmware or in an external device (e.g. associated
with a SAS expander). See http://www.t10.org for more information.
There is some support for SCSI tape devices but not for their basic
commands. The reader is referred to the "mt" utility.
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 typically 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
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 permit copying data at the level of SCSI READ and WRITE
commands. sg_dd is tightly bound to Linux and hence is not ported to
other OSes. A more generic utility (than sg_dd) called ddpt in a
package of the same name has been ported to other OSes.
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
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
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.
for SCSI commands that yield a non-trivial response, print out
that response in ASCII hexadecimal.
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.
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.
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.
print the version string and then exit. Each utility has its own
version number and date of last code change.
Many utilities have command line options that take numeric arguments.
These numeric arguments can be large values (e.g. a logical block
address (LBA) on a disk) and can be inconvenient to enter in the
default decimal representation. So various other representations are
Multiplicative suffixes are accepted. They are one, two or three letter
strings appended directly after the number to which they apply:
c C *1
w W *2
b B *512
k K KiB *1024
m M MiB *1048576
g G GiB *(2^30)
t T TiB *(2^40)
p P PiB *(2^50)
An example is "2k" for 2048. The large tera and peta suffixes are only
available for numeric arguments that might require 64 bits to represent
A suffix of the form "x<n>" multiplies the leading number by <n>. An
example is "2x33" for "66". The leading number cannot be "0" (zero) as
that would be interpreted as a hexadecimal number (see below).
These multiplicative suffixes are compatible with GNU’s dd command
(since 2002) which claims compliance with SI and with IEC 60027-2.
Alternatively numerical arguments can be given in hexadecimal. There
are two syntaxes. The number can be preceded by either "0x" or "0X" as
found in the C programming language. The second hexadecimal
representation is a trailing "h" or "H" as found in (storage)
standards. When hex numbers are given, multipliers cannot be used. For
example the decimal value "256" can be given as "0x100" or "100h".
SCRIPTS, EXAMPLES and UTILS
There are several bourne shell scripts in the ’scripts’ subdirectory
that invoke compiled utilities (e.g. sg_readcap). The scripts start
with ’scsi_’ rather than ’sg_’. One purpose of these scripts is to call
the same utility (e.g. sg_readcap) on multiple disks. Most of the basic
compiled utilities only allow one device as an argument. Some
distributions install these scripts in a visible directory (e.g.
/usr/src/bin). Some of these scripts have man page entries. See the
README file in the ’scripts’ subdirectory.
There is some example C code plus examples of complex invocations in
the ’examples’ subdirectory. There is also a README file. The example C
may be a simpler example of how to use a SCSI pass-through in Linux
than the main utilities (found in the ’src’ subdirectory). This is due
to the fewer abstraction layers (e.g. they don’t worry the MinGW in
Windows may open a file in text rather than binary mode).
Some utilities that the author has found useful have been placed in the
There is a web page discussing this package at
Written by Douglas Gilbert. Some utilities have been contributed, see
the CREDITS file and individual source files (in the ’src’ directory).
Report bugs to <dgilbert at interlog dot com>.
Copyright © 1999-2010 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.
sdparm(sdparm), ddpt(ddpt), mt(1)