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SG_MODES

Section: SG3_UTILS (8)
Updated: May 2023
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NAME

sg_modes - reads mode pages with SCSI MODE SENSE command

SYNOPSIS

sg_modes [--all] [--ALL] [--control=PC] [--dbd] [--dbout] [--examine] [--flexible] [--help] [--hex] [--list] [--llbaa] [--maxlen=LEN] [--multiple] [--page=PG[,SPG]] [--raw] [-R] [--readwrite] [--six] [--verbose] [--version] [DEVICE]

sg_modes [-6] [-a] [-A] [-c=PC] [-d] [-D] [-e] [-f] [-h] [-H] [-l] [-L] [-m=LEN] [-M] [-p=PG[,SPG]] [-r] [-subp=SPG] [-v] [-V] [-w] [-?] [DEVICE]

DESCRIPTION

This utility sends a MODE SENSE SCSI command to the DEVICE and outputs the response. There is a 6 byte and 10 byte (cdb) variant of the MODE SENSE command, this utility defaults to the 10 byte variant. The SPC-4 standard (and the SPC-5 standard) stated that implementers should migrate away from the SCSI MODE SELECT(6) and MODE SENSE(6) commands in favour of the 10 byte variants (e.g. MODE SENSE(10)). In draft SPC-6 revision 7 the SCSI MODE SELECT(6) and MODE SENSE(6) commands have been removed.

This utility decodes mode page headers and block descriptors but outputs the contents of each mode page in hex. It also has no facility to change the mode page contents or block descriptor data. Mode page contents are decoded and can be changed with the sdparm utility.

This utility supports two command line syntaxes, the preferred one is shown first in the synopsis and explained in this section. A later section on the old command line syntax outlines the second group of options.

If no page is given (and --list is not selected) then --all is assumed. The --all option requests all mode pages (but not subpages) in a single response.

OPTIONS

Arguments to long options are mandatory for short options as well.

-a, --all: output all the mode pages reported by the DEVICE. This is what the page code 63 (0x3f) is defined to do. When used once, mode subpages are not fetched. When used twice (e.g. '-aa'), all mode pages and subpages are requested which is equivalent to '--page=63,255'.
-A, --ALL: same meaning as using the --all option twice. That is, all mode pages and subpages are fetched. The default is to fetch all the mode pages but not mode subpages.
-c, --control=PC: PC is the page control value. Up to four different versions of each page are held by the device:
    0 : current values (i.e. those active at present)
    1 : changeable values
    2 : default values (i.e. the manufacturer's settings)
    3 : saved values
The changeable values are bit masks showing which fields could be changed with a MODE SELECT. The saved values will be re-instated the next time the device is power cycled or reset. If this option is not given then current values [0] are assumed.
-d, --dbd: disable block descriptors. By default, block descriptors (usually one (for disks) or none) are returned in a MODE SENSE response. This option sets the "disable block descriptors" (DBD) bit in the cdb which instructs the device not to return any block descriptors in its response. Older devices may not support this setting and may return an "illegal request" sense key; alternatively they may ignore it. Oddly the Reduced Block Command set (RBC) requires this bit set.
-D, --dbout: disable outputting block descriptors. Irrespective of whether block descriptors are present in the response or not, they are not output.
-e, --examine: if the --page=PG[,SPG] option is not given, examine each mode page in the range 0 through to 62 (inclusive). If the --page=PG[,SPG] option is give, then all subpages whose page code is PN are examined (subpages 0 through 254 (inclusive)). If some response is given then print out the mode (sub)page name or number (in hex) if the name is not known.
The sdparm utility which lists mode and VPD pages also has a --examine option will similar functionility.
-f, --flexible: Some devices, bridges and/or drivers attempt crude translations between MODE SENSE 6 and 10 byte commands without correcting the response. This will cause the response to be mis-interpreted (usually with an error saying the response is malformed). With this option, the length of the response is checked, and if it looks wrong, the response is then decoded as if the other mode sense (cdb length) was sent.
-h, --help: print out the usage message then exit.
-H, --hex: Since this utility shows the structure of a MODE SENSE command response (i.e. its parameter header, zero or more block descriptors followed by zero or more mode pages) but outputs most of the contents of the response in hexadecimal. When this option is used once, the only difference is that the mode page name, if known, is followed by it page number (and subpage number) bracketed in hex.
When this option is given twice, then each line of hex output has an ASCII rendering of that hex place at the end of each line. When this option is given three times, then the hexadimal address, shown at the start of each hexadecimal line is dropped, there is no ASCII rendering of hex, and all test lines are removed. This leaves simple hex that is parsable that represents the MODE SENSE command response. The component parts of that response are put on separate line.
When the option is given four or more times (recommended for a parsable form), the ASCII informational lines are back, but they all start with "#" which a parser needs to ignore. The output is sent to stdout while any error messages or warning are sent to stderr. So simple Unix command line redirection of stdout to a file (done with '>' in most Unix shells) should be sufficient to capture the output. As noted above, the sdparm utility can be used to decode that hex file later with its '--inhex=FN' option.
-l, --list: lists all common page and subpage codes and their names that are found in the command set that matches the peripheral type of the given DEVICE. If no DEVICE and no --page=PG is given then the common page and subpage codes and their names are listed for SBC (e.g. a disk). If no DEVICE is given and a --page=PG is given then the common page and subpage codes and their names are listed for the command set whose peripheral device type matches the value given to PG. For example 'sg_mode --list --page=1' lists the command mode pages and subpages for tape devices. Additionally if a sub_page_code is given then it is interpreted as a transport identifier and command transport specific mode page codes and their names are listed following the main mode page list. Other options are ignored.
-L, --llbaa: set the Long LBA Accepted (LLBAA) bit in the MODE SENSE (10) cdb. This bit is not defined in the MODE SENSE (6) cdb so setting the '-L' and '--six' options is reported as an error. When set the DEVICE may respond with 16 byte block descriptors as indicated by the 'LongLBA' field in the response. In most cases setting this option is not needed.
-m, --maxlen=LEN: The LEN argument is the maximum response length in bytes. It is the 'allocation length' field in the cdb. When not given (or LEN is zero) then the allocation length field is set to 4096 for MODE SENSE (10) or 252 for MODE SENSE (6). The LEN argument must be non-negative and no greater than 65535 for MODE SENSE (10) and not greater than 255 for MODE SENSE (6).
-M, --multiple: for each mode page (and mode subpage), fetch all available page controls. There may be up to four page controls as outlined in the --control=PC option. The mode parameter header, and block descriptors are output that same way as without this option. After the mode page name (and numbers) are output, there is a line with either current, changeable, default or saved page control on it followed by that page control in hex.
If the --control=PC option is given, it is overridden by this option.
-O, --old: Switch to older style options. Please use as first option.
-p, --page=PG: page code to fetch. The PG is assumed to be a decimal value unless prefixed by '0x' or has a trailing 'h'. It should be a value between 0 and 63 (inclusive). When not given and a default is required then a value of 63 (0x3f), which fetches all mode pages, is used.
Alternatively an acronym for the mode page can be given. The available acronyms can be listed out with the --page=xxx option. They are almost the same as the acronyms used for mode pages in the sdparm utility.
-p, --page=PG,SPG: page code and subpage code values to fetch. Both arguments are assumed to be decimal unless flagged as hexadecimal. The page code should be between 0 and 63 inclusive. The subpage code should be between 0 and 255 inclusive. The default value for the subpage code is 0.
-r, --raw: output the response in binary to stdout. Error messages and warnings, if any, are sent to stderr. When this option is used twice (e.g. '-rr') then has the same action as '-R'
-R: output the selected mode page to stdout a byte per line. Each line contains two hexadecimal digits (e.g. "3e"). Useful as input (after editing) to the sg_wr_mode(8) utility.
-w, --readwrite: open DEVICE in "read-write" mode. Default is to open it in read-only mode.
-6, -s, --six: by default this utility sends a 10 byte MODE SENSE command to the DEVICE. However some SCSI devices only support 6 byte MODE SENSE commands (e.g. SCSI-2 tape drives). This parameter forces the use of 6 byte MODE SENSE commands.
-v, --verbose: increase level of verbosity. Can be used multiple times.
-V, --version: print out version string then exit.

NOTES

If the normal sg_modes utility fails with "illegal command operation code" then try the '--six' (or '-6') option.

This utility performs a SCSI INQUIRY command to determine the peripheral type of the device (e.g. 0 -> Direct Access Device (disk)) prior to sending a MODE SENSE command. This helps in decoding the block descriptor and mode pages.

This utility opens DEVICE in read-only mode (e.g. in Unix, with the O_RDONLY flag) by default. It will open DEVICE in read-write mode if the --readwrite option is given.

In the 2.4 series of Linux kernels the DEVICE must be a SCSI generic (sg) device. In the 2.6 series block devices (e.g. SCSI disks and DVD drives) can also be specified. For example "sg_modes -a /dev/sda" will work in the 2.6 series kernels.

There is no JSON output from this utility because its primary output is mode pages in hexadecimal. So apart from the mode page name and its structure, nothing is decoded. The sdparm utility does decode mode page contents and it does support JSON output.

EXIT STATUS

The exit status of sg_modes is 0 when it is successful. Otherwise see the sg3_utils(8) man page.

OLDER COMMAND LINE OPTIONS

The options in this section were the only ones available prior to sg3_utils version 1.23 . Since then this utility defaults to the newer command line options which can be overridden by using --old (or -O) as the first option. See the ENVIRONMENT VARIABLES section for another way to force the use of these older command line options.

-6: by default this utility sends a 10 byte MODE SENSE command to the DEVICE. This parameter forces the use of 6 byte MODE SENSE commands. See --six in the main description.
-a: see --all in the main description.
-A: output all the mode pages and subpages supported by the DEVICE. Same as '--all --all' in the new syntax.
-c=PC: PC is the page control value. See --control=PC in the main description.
-d: see --dbd in the main description.
-D: see --dbout in the main description.
-e: see --examine in the main description.
-f: see --flexible in the main description.
-h: The default action is to decode known mode page numbers (and subpage numbers) into text. With this option mode page numbers (and subpage numbers) are output in hexadecimal.
-H: same action as the '-h' option.
-l: see --list in the main description.
-L: see --llbaa in the main description.
-N, --new: Switch to the newer style options.
-m=LEN: see --maxlen=LEN in the main description.
-M: see --multiple in the main description.
-p=PG: PG is page code to fetch. Should be a hexadecimal number between 0 and 3f inclusive (0 to 63 decimal). The default value when required is 3f (fetch all mode pages). Note that an acronym for the page and/or subpage values is not accepted in this older format (because any acronym starting with the letters 'a' to 'f' is ambiguous; it could either be a hex number or an acronym).
-p=PG,SPG: page code and subpage code values to fetch. The page code should be a hexadecimal number between 0 and 3f inclusive. The subpage code should be a hexadecimal number between 0 and ff inclusive. The default value for the subpage code is 0.
-r: output the selected mode page to stdout a byte per line. Each line contains two hexadecimal digits (e.g. "3e"). Useful as input (after editing) to the sg_wr_mode(8) utility.
-subp=SPG: sub page code to fetch. Should be a hexadecimal number between 0 and 0xff inclusive. The default value is 0.
-v: increase verbosity of output.
-V: print out version string then exit.
-w: see --readwrite in the main description.
-?: output usage message then exit. Ignore all other parameters.

ENVIRONMENT VARIABLES

Since sg3_utils version 1.23 the environment variable SG3_UTILS_OLD_OPTS can be given. When it is present this utility will expect the older command line options. So the presence of this environment variable is equivalent to using --old (or -O) as the first command line option.

EXAMPLES

All mode pages, but not mode subpages, can be dumped in hex to a file like this:

# sg_modes -a -HHHH /dev/sdb > modes_sdeb.hex

If there are any errors then they are sent to stderr so they will appear on the console and not within the modes_sdeb.hex file. Nonetheless the contents of modes_sdeb.hex may not be useful if an error has occurred.

The '-HHHH' option produces hex output with comment lines starting with a '#' character. Each comment describes the following block. If all is well, the modes_sdeb.hex file will be suitable for the sdparm utility to decode:

# sdparm -a --inhex=modes_sdeb.hex

See the sdparm(8) manpage for further information.
To dump both mode pages and subpages, use this invocation:

# sg_modes -aa -HHHH /dev/sdb > modes_sdeb.hex

No change is needed in the associated sdparm call. There is some example output in the inhex directory in the sg3_utils package, in a file called: modes_sdeb.hex . The file was produced by using this utility on the scsi_debug driver in Linux.

Each mode page (and subpage) has up to four 'page controls': current, changeable, default and saved. The last three may or may not be supported by the device. All available page controls for all mode pages and subpages can be placed in a hex file with this invocation:

# sg_modes -aa -M -HHHH /dev/sdb > modes_mm_sdeb.hex

Again, no change is needed in the associated sdparm call. There is some example output in the inhex directory in the sg3_utils package, in a file called: modes_mm_sdeb.hex .

AUTHOR

Written by Douglas Gilbert

REPORTING BUGS

Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT

This document was created by man2html, using the manual pages.
Time: 04:00:44 GMT, August 02, 2023