Ubuntu Manpage: sg_wr_mode - write (modify) SCSI mode page

Provided by: sg3-utils_1.36-1ubuntu1_amd64

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[,SPG]] [--save] [--verbose] [--version] DEVICE

DESCRIPTION

Writes a modified mode page to DEVICE. Uses the SCSI MODE SENSE (6 or 10 byte variant)
command to fetch the existing mode data which includes a mode page (or subpage). It then
combines 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 descriptor(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 a contents argument is not given then the various components (i.e. header, block
descriptor(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
corresponding to set bits in the mask are taken while the existing mode page supplies bit
positions 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 suppressed with the --dbd option if need be.

Changing individual fields in a mode page is probably more easily done with the sdparm
utility. 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  characters  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
              descriptors in the mode data returned by a MODE SENSE command. If so the same block
              descriptors 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  existing 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
              where PG 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,SPG
              where PG is the page code value and SPG 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.

       -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.

       -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
       SELECT  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
       condition" 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>.

COPYRIGHT

       Copyright © 2004-2012 Douglas Gilbert
       This  software  is distributed under a FreeBSD license. There is NO warranty; not even for
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.