--- name: "sg_luns" section: "8" platform: "linux" package: "sg3_utils" version: "1.49-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/sg_luns" --- # sg\_luns(8) send SCSI REPORT LUNS command or decode given LUN ## NAME sg\_luns - send SCSI REPORT LUNS command or decode given LUN ## SYNOPSIS **sg\_luns** \[*--decode*\] \[*--help*\] \[*--hex*\] \[*--inhex=FN*\] \[*--inner-hex*\] \[*--json\[=JO\]*\] \[*--js-file=JFN*\] \[*--linux*\] \[*--lu\_cong*\] \[*--maxlen=LEN*\] \[*--quiet*\] \[*--raw*\] \[*--readonly*\] \[*--select=SR*\] \[*--sinq\_inraw=RFN*\] \[*--verbose*\] \[*--version*\] *DEVICE* **sg\_luns** *--test=ALUN* \[*--decode*\] \[*--hex*\] \[*--inner-hex*\] \[*--lu\_cong*\] \[*--verbose*\] ## 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 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. 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. Notice that this (i.e. how '-HH' is processed) differs from the description in [sg3\_utils(8)](/sg3_utils/8.md). The *--inner-hex* option has the same action as '-HH'. When this option is used three (or more) times the hex output is suitable for placing in a file and using it with a later sg\_luns invocation with the *--inhex=FN* option.\ \[test mode\] when this option is given, then decoded component fields of *ALUN* are output in hex.\ When this option is given three or more times, ASCII hex bytes are output (up to 16 per line) with no leading address or index. This output is suitable for placing in a file and later invocation of this utility decoding it with the *--inhex=FN* option. When this option is used four times, a comment line (starting with '#' is added before the hex) describing what the hex was generated by. A file containing such comments is still parsable by the *--inhex=FN* option. - **-i**, **--inhex**=*FN* *FN* is expected to be a file name (or '-' for stdin) which contains ASCII hexadecimal or binary representing a REPORT LUNS response. This utility will then decode that response. See the "HEX, BINARY AND JSON FORMATS" section in the sg3\_utils manpage for more information. If the *--raw* option is also given then *FN* is treated as binary. - **-I**, **--inner-hex** used together with the *--decode* option so that the decoded values are shown in hexadecimal. The default action is to show decoded values in decimal. This option has the same action as '-HH' but the intent is a little clearer with this option. - **-j**\[=*JO*\], **--json**\[=*JO*\] output is in JSON format instead of plain text form. Note that arguments to the short and long form are themselves optional and if present start with "=" and no whitespace is permitted around that "=".\ See sg3\_utils\_json manpage or use '?' for *JO* to get a summary. - **-J**, **--js-file**=*JFN* output is in JSON format and it is sent to a file named *JFN*. If that file exists then it is truncated. By default, the JSON output is sent to stdout.\ When this option is given, the *--json\[=JO\]* option is implied and need not be given. The *--json\[=JO\]* option may still be needed to set the *JO* parameter to non-default values. - **-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 INQUIRY 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**=*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). - **-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* *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* . - **-Q**, **--sinq\_inraw**=*RFN* where *RFN* is a filename containing binary standard INQUIRY response data that matches either *DEVICE* or *FN*. Linux places this standard INQUIRY response in its sysfs pseudo filesystem. A typical location is at /sys/class/scsi\_device/\/device/inquiry where \ is a four part numeric tuple separated by colons. This tuple distinguishes the device from any others on the system.\ Currently the LU\_CONG field is read from the standard INQUIRY response when this option is given. The *--raw* option has no effect on this option. The *DEVICE* argument may be given with this option. - **-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 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 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.\ 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 INQUIRY 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 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, 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 implies 2 lun entries\ 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 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 \[1\]\ 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)](/sg3_utils/8.md) man page. ## AUTHORS Written by Douglas Gilbert. ## REPORTING BUGS Report bugs to \. ## COPYRIGHT Copyright © 2004-2023 Douglas Gilbert\ This software is distributed under a BSD-2-Clause license. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. ## SEE ALSO **[sg\_inq(8)](/sg_inq/8.md),[sg3\_utils(8)](/sg3_utils/8.md)**