# sg_luns - send SCSI REPORT LUNS command or decode given LUN - man(8) - [phpMan] [_SG_LUNS_(8)](https://www.chedong.com/phpMan.php/man/SGLUNS/8/markdown) SG3_UTILS [_SG_LUNS_(8)](https://www.chedong.com/phpMan.php/man/SGLUNS/8/markdown) ## NAME sg_luns - send SCSI REPORT LUNS command or decode given LUN ## SYNOPSIS **sg_luns **[_--decode_] [_--help_] [_--hex_] [_--linux_] [_--lu_cong_] [_--maxlen=LEN_] [_--quiet_] [_--raw_] [_--readonly_] [_--select=SR_] [_--verbose_] [_--version_] _DEVICE_ **sg_luns _**--test=ALUN_ [_--decode_] [_--hex_] [_--lu_cong_] [_--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 inven‐ tory") 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. This command is defined in the SPC-3 and SPC-4 SCSI standards and its support is mandatory. The most recent draft if SPC-6 revision 1. When the _--test=ALUN_ option is given (the second form in the SYNOPSIS), then the _ALUN_ value is decoded as outlined in various SCSI Architecture Model (SAM) standards and recent drafts (e.g. SAM-6 revision 2, 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. [test mode] _ALUN_ is decoded irrespective of whether this option is given or not. If this option is given once then the given _ALUN_ is output in T10 preferred format (which is 8 pairs of hex digits, each separated by a space). If given twice then the given _ALUN_ is output in an alternate T10 format made up of four quads of hex digits with each quad separated by a "-" (e.g. C101-0000-0000-0000). ### -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. [test mode] when this option is given, then decoded component fields of _ALUN_ are out‐ put in hex. ### -l --linux this option is only available in Linux. After the T10 representation 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. ### -L --lu_cong this option is only considered with _--decode_. When given once then the list of LUNs is decoded as if the LU_CONG bit was set in each LU's corresponding INQUIRY response. When given twice the list of LUNs is decoded as if the LU_CONG bit was clear in each LU's corresponding INQUIRY response. When this option is not given and _--decode_ is given then an INQUIRY is sent to the _DEVICE_ and the setting of its LU_CONG bit is used to decode the list of LUNs. [test mode] decode _ALUN_ as if the LU_CONG bit is set in its corresponding standard IN‐ QUIRY response. In other words treat _ALUN_ as if it is a conglomerate LUN. If not given (or given twice) then decode _ALUN_ as if the LU_CONG bit is clear. ### -m --maxlen where _LEN_ is the (maximum) response length in bytes. It is placed in the cdb's "allo‐ cation length" field. If not given (or _LEN_ is zero) then 8192 is used. The maximum al‐ lowed 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). ### -R --readonly open the _DEVICE_ read-only (e.g. in Unix with the O_RDONLY flag). The default is to open it read-write. ### -s --select _SR_ is placed in the SELECT REPORT field of the SCSI REPORT LUNS command. The default value is 0. Hexadecimal values may be given with a leading "0x" or a trailing "h". For detailed information see the REPORT LUNS command in SPC (most recent is SPC-4 revision 37 in section 6.33). To simplify, for the I_T nexus associated with the _DEVICE_, the meanings of the _SR_ values defined to date for SPC-4 are: **0 **: most luns excluding well known logical unit numbers **1 **: well known logical unit numbers **2 **: all luns accessible to this I_T nexus **0x10 **: only accessible administrative luns **0x11 **: administrative luns plus non-conglomerate luns (see SPC-4) **0x12 **: if _DEVICE_ is an administrative LU, then report its lun plus its subsidiary luns For _SR_ values 0x10 and 0x11, the _DEVICE_ must be either LUN 0 or the REPORT LUNS well known logical unit. Values between 0xf8 and 0xff (inclusive) are vendor specific, other values are reserved. This utility will accept any value between 0 and 255 (0xff) for _SR_ . ### -t --test _ALUN_ is assumed to be a hexadecimal number in ASCII hex or the letter 'L' followed by a decimal number (see below). The hexadecimal 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: 01 22 00 3a 00 00 00 00). _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, tabs, or a '-' between each byte (or other grouping (e.g. c101-0000-0000-0000)). However in the case of space or tab separators the _ALUN_ would need to be surrounded by single or double quotes. In the leading 'L' case the, following decimal number (hex if preceded by '0x') is as‐ sumed to be a Linux "word flipped" LUN which is converted into a T10 LUN representa‐ tion 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 out‐ put. The LUN is decoded in all cases. The action when used with _--decode_ is explained under that option. ### -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) discovery. After a target device is discovered (usually via some transport specific mechanism) and after sending an IN‐ QUIRY command (to determine the LU_CONG setting), a REPORT LUNS command should either be sent to LUN 0 (which is Peripheral device addressing method with bus_id=0 and target/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 com‐ ponent 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, target=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 [6:0:0:2] disk Linux scsi_debug 0004 /dev/sdc /dev/sg2 [6:0:0:49409]wlun Linux scsi_debug 0004 - /dev/sg3 We could send a REPORT LUNS command (with _SR_ 0x0, 0x1 or 0x2) to any of those file device nodes and get the same result. Below we use /dev/sg1 : # sg_luns /dev/sg1 Lun list length = 16 which imples 2 lun entry Report luns [select_report=0x0]: 0001000000000000 0002000000000000 That is a bit noisy so cut down the clutter with _--quiet_: # sg_luns -q /dev/sg1 0001000000000000 0002000000000000 Now decode that LUN into its component parts: # sg_luns -d -q /dev/sg1 0001000000000000 Peripheral device addressing: lun=1 0002000000000000 Peripheral device addressing: lun=2 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 0002000000000000 c101000000000000 # sg_luns -q -s 2 -d /dev/sg1 0001000000000000 Peripheral device addressing: lun=1 0002000000000000 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 sys‐ tems. 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] 0002000000000000 [2] 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=0002000000000000 Decoded LUN: Peripheral device addressing: lun=2 # 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)](https://www.chedong.com/phpMan.php/man/sg3utils/8/markdown) man page. ## AUTHORS Written by Douglas Gilbert. ## REPORTING BUGS Report bugs to . ## COPYRIGHT Copyright © 2004-2020 Douglas Gilbert This software is distributed under a FreeBSD license. There is NO warranty; not even for MER‐ CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. ## SEE ALSO ### [sg_inq(8)](https://www.chedong.com/phpMan.php/man/sginq/8/markdown) sg3_utils-1.45 January 2020 [_SG_LUNS_(8)](https://www.chedong.com/phpMan.php/man/SGLUNS/8/markdown)