sg_luns man page on Slackware
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SG_LUNS(8) SG3_UTILS SG_LUNS(8)
NAME
sg_luns - send SCSI REPORT LUNS command or decode given LUN
SYNOPSIS
sg_luns [--decode] [--help] [--hex] [--linux] [--maxlen=LEN] [--quiet]
[--raw] [--select=SR] [--verbose] [--version] DEVICE
sg_luns --test=ALUN [--hex] [--verbose]
DESCRIPTION
In the first form shown in the SYNOPSIS this utility sends the SCSI
REPORT LUNS command to the DEVICE and outputs the response. The
response should be a list of LUNs ("a LUN inventory") for the I_T nexus
associated with the DEVICE. Roughly speaking that is all LUNs that
share the target device that the REPORT LUNS command is sent through.
In the SPC-3 and SPC-4 SCSI standards support for the REPORT LUNS com‐
mand is mandatory.
When the --test=ALUN option is given (the second form in the SYNOPSIS),
then the ALUN value is decoded as outlined in SAM-3, SAM-4 and SAM-5
(revision 13, section 4.7) .
Where required below the first form shown in the SYNOPSIS is called
"device mode" and the second form is called "test mode".
OPTIONS
Arguments to long options are mandatory for short options as well.
-d, --decode
decode LUNs into their component parts, as described in the LUN
section of SAM-3, SAM-4 and SAM-5.
-h, --help
output the usage message then exit.
-H, --hex
[device mode] when given once this utility will output the SCSI
response (i.e. the data-out buffer) to the REPORT LUNS command
in ASCII hex then exit. When given twice it causes --decode to
output component fields in hex rather than decimal.
-H, --hex
[test mode] when this option is given, then decoded component
fields of ALUN are output in hex.
-l, --linux
this option is only available in Linux. After the T10 represen‐
tation of each 64 bit LUN (in 16 hexadecimal digits), if this
option is given then to the right, in square brackets, is the
Linux LUN integer in decimal. If the --hex option is given
twice (e.g. -HH) as well then the Linux LUN integer is output in
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 8192 is used. The maximum allowed value of LEN
is 1048576.
-q, --quiet
output only the ASCII hex rendering of each report LUN, one per
line. Without the --quiet option, there is header information
printed before the LUN listing.
-r, --raw
output the SCSI response (i.e. the data-out buffer) in binary
(to stdout).
-s, --select=SR
this option sets the SELECT REPORT field (SR) in the SCSI REPORT
LUNS command. The default value is 0. For detailed information
see the REPORT LUNS command in SPC (most recent is SPC-4 revi‐
sion 36e in section 6.33). To simplify, for the I_T nexus asso‐
ciated with the DEVICE, the meanings of the SR values defined to
date for SPC-4 are:
0 : all LUNs excluding well known logical units
1 : well known logical units
2 : all LUNs
Values between 0xf8 and 0xff (inclusive) are vendor specific
(SPC-4 rev 36e), other values greater than 2 are reserved. This
utility will accept any value between 0 and 255 (0xff) for SR .
-t, --test=ALUN
ALUN is assumed to be a hexadecimal number in ASCII hex or the
letter 'L' followed by a decimal number (see below). The hexa‐
decimal number can be up to 64 bits in size (i.e. 16 hexadecimal
digits) and is padded to the right if less than 16 hexadecimal
digits are given (e.g. --test=0122003a represents T10 LUN
0122003a00000000). ALUN may be prefixed by '0x' or '0X' (e.g.
the previous example could have been --test=0x0122003a). ALUN
may also be given with spaces or tabs between each byte (or
other grouping) but then ALUN would need to be surrounded by
single or double quotes. In the decimal number case (i.e. fol‐
lowing a 'L') that number is assumed to be a Linux "word
flipped" LUN which is converted into a T10 LUN representation
and printed. In both cases the number is interpreted as a LUN
and decoded as if the --decode option had been given. Also when
ALUN is a hexadecimal number it can have a trailing 'L' in which
case the corresponding Linux "word flipped" LUN value is output.
The LUN is decoded in all cases.
-v, --verbose
increase the level of verbosity, (i.e. debug output).
-V, --version
print the version string and then exit.
NOTES
The SCSI REPORT LUNS command is important for Logical Unit (LU) discov‐
ery. After a target device is discovered (usually via some transport
specific mechanism), a REPORT LUNS command should either be sent to LUN
0 (which is Peripheral device addressing method with bus_id=0 and tar‐
get/lun=0) or to the REPORT LUNS well known LUN (i.e.
0xc101000000000000). SAM-5 requires that one of these responds with an
inventory of LUNS that are contained in this target device.
In test mode, if the --hex option is given once then in the decoded
output, some of the component fields are printed in hex with leading
zeros. The leading zeros are to indicate the size of the component
field. For example: in the Peripheral device addressing method (16 bits
overall), the bus ID is 6 bits wide and the target/LUN field is 8 bits
wide; so both are shown with two hex digits (e.g. bus_id=0x02, tar‐
get=0x3a).
EXAMPLES
Typically by the time user space programs get to run, SCSI LUs have
been discovered. In Linux the lsscsi utility lists the LUs that are
currently present. The LUN of a device (LU) is the fourth element in
the tuple at the beginning of each line. Below we see a target (or "I_T
Nexus": "6:0:0") has two LUNS: 1 and 49409. If 49409 is converted into
T10 LUN format it is 0xc101000000000000 which is the REPORT LUNS well
known LUN.
# lsscsi -g
[6:0:0:1] disk Linux scsi_debug 0004 /dev/sdb
/dev/sg1
[6:0:0:49409]wlun Linux scsi_debug 0004 -
/dev/sg2
We could send a REPORT LUNS command to either /dev/sdb, /dev/sg1 or
/dev/sg2 and get the same result. Below we use /dev/sg1 :
# sg_luns /dev/sg1
Lun list length = 8 which imples 1 lun entry
Report luns [select_report=0x0]:
0001000000000000
That is a bit noisy so cut down the clutter with --quiet:
# sg_luns -q /dev/sg1
0001000000000000
Now decode that LUN into its component parts:
# sg_luns -d -q /dev/sg1
0001000000000000
Peripheral device addressing: lun=1
Would like to see how wide that component LUN field is:
# sg_luns -d -q -HH /dev/sg1
0001000000000000
Peripheral device addressing: lun=0x01
So it is 8 bits wide (actually between 5 and 8 bits wide, inclusive).
Now use --select=1 to find out if there are any well known LUNs:
# sg_luns -q -s 1 /dev/sg1
c101000000000000
So how many LUNs do we have all together (associated with the current
I_T Nexus):
# sg_luns -q -s 2 /dev/sg1
0001000000000000
c101000000000000
# sg_luns -q -s 2 -d /dev/sg1
0001000000000000
Peripheral device addressing: lun=1
c101000000000000
REPORT LUNS well known logical unit
The following example uses the --linux option and is not available in
other operating systems. The extra number in square brackets is the
Linux version of T10 LUN shown at the start of the line.
# sg_luns -q -s 2 -l /dev/sg1
0001000000000000 [1]
c101000000000000 [49409]
Now we use the --test= option to decode LUNS input on the command line
(rather than send a REPORT LUNS command and act on the response):
# sg_luns --test=0001000000000000
Decoded LUN:
Peripheral device addressing: lun=1
# sg_luns --test="c1 01"
Decoded LUN:
REPORT LUNS well known logical unit
# sg_luns -t 0x023a004b -H
Decoded LUN:
Peripheral device addressing: bus_id=0x02, target=0x3a
>>Second level addressing:
Peripheral device addressing: lun=0x4b
The next example is Linux specific as we try to find out what the Linux
LUN 49409 translates to in the T10 world:
# sg_luns --test=L49409
64 bit LUN in T10 preferred (hex) format: c1 01 00 00 00 00 00 00
Decoded LUN:
REPORT LUNS well known logical unit
And the mapping between T10 and Linux LUN representations can be done
the other way:
# sg_luns -t c101L
Linux 'word flipped' integer LUN representation: 49409
Decoded LUN:
REPORT LUNS well known logical unit
EXIT STATUS
The exit status of sg_luns 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 © 2004-2013 Douglas Gilbert
This software is distributed under a FreeBSD license. There is NO war‐
ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
POSE.
SEE ALSO
sg_inq(8)
sg3_utils-1.36 May 2013 SG_LUNS(8)
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