sg_wr_mode(8) - man - phpman

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SG_WR_MODE(8) SG3_UTILS SG_WR_MODE(8)

NAME
sg_wr_mode - write (modify) SCSI mode page

SYNOPSIS
sg_wr_mode [--contents=H,H...] [--dbd] [--force] [--help] [--len=10|6] [--mask=M,M...]
[--page=PG_H[,SPG_H]] [--rtd] [--save] [--six] [--verbose] [--version] DEVICE

DESCRIPTION
Writes a modified mode page to DEVICE. Uses the SCSI MODE SENSE (6 or 10 byte variant) com‐
mand to fetch the existing mode data which includes a mode page (or subpage). It then com‐
bines that with the contents, potentially masked, and writes the modified mode page with the
SCSI MODE SELECT (6 or 10 byte variant) command. This utility does not modify the block de‐
scriptor(s); if any block descriptors are fetched by the MODE SENSE command then the same
block descriptors are written back with the following MODE SELECT command.

If the --rtd option is given then most other options apart from --save, --len=10|6 and --six
are ignored. In this case only a MODE SELECT command is sent to the DEVICE with the RTD bit
(Revert To Defaults) set. This bit was added to this command in SPC-5 revision 11, so older
devices may not support it. The Extended Inquiry VPD page has the RTD_SUP bit to indicate
whether the DEVICE supports the RTD bit in the MODE SELECT(6 and 10) commands. When the --rtd
option is given the rest of this section can be ignored.

If a contents argument is not given then the various components (i.e. header, block descrip‐
tor(s) and mode page) of the "current" values of the existing mode page are printed out. In
this case the mode page is not altered on the device.

If the contents are specified, and a mask is not specified, then the contents must match the
existing mode page in various aspects unless the --force option is given. These include
length, mode page code and subpage code if applicable. If all is well then the contents
string is written to DEVICE as the new mode page.

If both contents and mask strings are specified then only bit positions in the contents cor‐
responding to set bits in the mask are taken while the existing mode page supplies bit posi‐
tions corresponding to clear bits. When a mask is given then the mask and/or the contents
may be shorter than the existing mode page. If the mask is shorter than the contents then the
remaining bytes are taken from the contents. If the contents are shorter than the existing
mode page then the remaining bytes are taken from the existing mod page.

The force option allows the contents string to be written as the new mode page without any
prior checks on the existing mode page. This should only be required for vendor specific mode
pages. The existing mode data is ignored apart from the block descriptors which can be sup‐
pressed with the --dbd option if need be.

Changing individual fields in a mode page is probably more easily done with the sdparm util‐
ity. Fields can be identified by acronym or by a numerical descriptor.

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

-c, --contents=H,H...
where H,H... is a string of comma separated hex numbers each of which should resolve
to a byte value (i.e. 0 to ff inclusive). A (single) space separated string of hex
numbers is also allowed but the list needs to be in quotes. This is the new contents
of the mode page to be written to DEVICE, potentially filtered by the mask string.

-c, --contents=-
reads contents string from stdin. The hex numbers in the string may be comma, space,
tab or linefeed (newline) separated. If a line contains "#" then the remaining charac‐
ters on that line are ignored. Otherwise each non separator character should resolve
to a byte value (i.e. 0 to ff inclusive). This forms the new contents of the mode page
to be written to DEVICE, potentially filtered by the mask string.

-d, --dbd
disable block descriptors (DBD flag in cdb). Some device types include block descrip‐
tors in the mode data returned by a MODE SENSE command. If so the same block descrip‐
tors are written by the MODE SELECT command. This option instructs the MODE SENSE
command not to return any block descriptors. This would be a sensible default for this
utility apart from the fact that not all SCSI devices support the DBD bit in the cdb.

-f, --force
force the contents string to be taken as the new mode page, or at least doesn't do
checks on the existing mode page. Note that DEVICE may still reject the new contents
for the mode page. Cannot be given with the --mask=M,M... option.

-h, --help
output the usage message then exit.

-l, --len=10 | 6
length of the SCSI commands (cdb) sent to DEVICE. The default is 10 so 10 byte MODE
SENSE and MODE SELECT commands are issued. Some old devices don't support the 10 byte
variants hence this option.

-m, --mask=M,M...
where M,M... is a string of comma separated hex numbers each of which should resolve
to a byte value (i.e. 0 to ff inclusive). A (single) space separated string of hex
numbers is also allowed but the list needs to be in quotes. The mask chooses (bit by
bit) whether the new mode page comes from the contents (mask bit set) or from the ex‐
isting mode page (mask bit clear). If the mask string is shorter than the contents
string then the remaining bytes are taken from the contents string. If the contents
string is shorter than the existing mode page then the remaining bytes are taken from
the existing mode page (i.e. they are left unaltered).

-p, --page=PG_H
where PG_H is the page code value to fetch and modify. The page code is in hex and
should be between 0 and 3e inclusive. Notice that page code 3f to fetch all mode pages
is disallowed.

-p, --page=PG_H,SPG_H
where PG_H is the page code value and SPG_H is the subpage code value to fetch and
modify. Both values are in hex. The subpage code should be between 0 and fe inclusive.
Notice that subpage code ff to fetch all mode subpages (for a given mode page or all
mode pages in the case of 3f,ff) is disallowed.

-R, --rtd
when this option is given most other actions are bypassed and a MODE SELECT(6 or 10)
command is sent to the DEVICE with the RTD bit set. This will cause all current val‐
ues (and saved values if the --save option is also given) of all mode pages to be re‐
verted to their default values.

-s, --save
changes the "saved" mode page when MODE SELECT is successful. By default (i.e. when
--save is not used) only the "current" mode page values are changed when MODE SELECT
is successful. In this case the new mode page will stay in effect until the device is
reset (e.g. power cycled). When it restarts the "saved" values for the mode page
will be re-instated. So to make changes permanent use the --save option.
When used with the --rtd option then both the current and saved values in each mode
page are reverted to their default values. In the absence of --save option only the
current values in each mode page are reverted to their default values.

-6, --six
this option will cause the 6 byte variants of MODE SENSE and MODE SELECT commands to
be used. The default is to use the 10 byte options. This option is equivalent to using
the --len=6 option.

-v, --verbose
increase the level of verbosity, (i.e. debug output).

-V, --version
print the version string and then exit.

NOTES
This utility does not check whether the contents string is trying to modify parts of the mode
page which are changeable. The device should do that and if some part is not changeable then
it should report: "Invalid field in parameter list".

Some mode pages are not saveable. If so an attempt to use the --save option should cause an
error to be reported from the device: "Illegal field in cdb".

The device is required to do various checks before it accepts a new mode page. If these
checks fail then the mode page is not altered and either a "parameter list length error" or
an "invalid field in parameter list" error is returned by the device in the sense data.

The recommended way to modify a mode page is to read it with a MODE SENSE, modify some part
of it then write it back to the device with a MODE SELECT command. For example, reading an
existing mode page can be accomplished with 'sg_modes -p=1a -r /dev/sdb > mp_1a.txt' (the
power condition mode page). The mp_1a.txt file can be edited and then used as the contents
string to this utility (e.g. 'sg_wr_mode -p 1a -s -c - /dev/sdb < mp_1a.txt').

Two fields differ between what is read from the device with MODE SENSE and what is written to
the device with MODE SELECT: the mode data length is reserved (i.e. zero(es)) in a MODE SE‐
LECT command while the PS bit ((sub)page byte 0 bit 7) in each mode (sub)page is reserved
(zero) in a MODE SELECT command. The PS bit given in the contents string is zeroed unless
the --force option is selected.

EXAMPLES
This utility can be used together with the sg_modes utility. To re-instate the default mode
page values (i.e. the mode page values chosen by the manufacturer of the device) as both the
current and saved mode page values the following sequence could be used:

$ sg_modes --control=2 --page=1a -r /dev/sda > t
$ sg_wr_mode --page=1a --contents=- --save /dev/sda < t

Next is an example of using a mask to modify the "idle condition counter" of the "power con‐
dition" mode page (0x1a) from 0x28 to 0x37. Note that the change is not saved so the "idle
condition counter" will revert to 0x28 after the next power cycle. The output from sg_modes
is abridged.

$ sg_modes --page=1a /dev/hdc
>> Power condition (mmc), page_control: current
00 1a 0a 00 03 00 00 00 28 00 00 01 2c

$ sg_wr_mode -p 1a -c 0,0,0,0,0,0,0,37 -m 0,0,0,0,0,0,0,ff /dev/hdc

$ sg_modes -p 1a /dev/hdc
>> Power condition (mmc), page_control: current
00 1a 0a 00 03 00 00 00 37 00 00 01 2c

EXIT STATUS
The exit status of sg_wr_mode 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>.

SEE ALSO
sdparm(sdparm), sg_modes(sg3_utils), sginfo(sg3_utils)

sg3_utils-1.43 April 2018 SG_WR_MODE(8)