NAME

       scsi_ch_swp - change SCSI Software WRITE Protect and block device settings

SYNOPSIS

       scsi_ch_swp [--help] [--set 0|1] [--verbose] [--wr] BLK_DEVICE

DESCRIPTION

       This  bash shell script attempts to read or change the Software Write Protect (SWP) bit in
       the SCSI Control mode page using the sdparm utility.  If that change is successful then it
       uses  the  blockdev  utility  to  change  BLK_DEVICE's  read-write or read-only setting in
       sympathy. This script is only available in Linux  since  the  blockdev  utility  is  Linux
       specific.

       If  changing  the  SWP bit is supported, setting the SWP bit makes BLK_DEVICE read-only at
       the device (disk) itself. Clearing the  SWP  bit  makes  BLK_DEVICE  read-write  which  is
       usually the default setting at device (disk) power up.

       If  no  options  are  given  then  the  current state of the SWP bit is printed out (using
       sdparm) together with blockdev's RO bit.  If  they  are  both  1  then  BLK_DEVICE  is  in
       read-only mode; if they are both 0 then BLK_DEVICE is in read-write mode.

OPTIONS

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

       -h, --help
              print out the usage message then exit.

       -s, --set 0|1
              when  0  is  given  then the SWP bit in the Control mode page is cleared (i.e.  set
              that bit to 0) using sdparm; and blockdev is used to set BLK_DEVICE  to  read-write
              mode.  When  1  is  given  then  the  SWP bit in the Control mode page is set using
              sdparm; and blockdev is used to set BLK_DEVICE to read-only mode. The default (i.e.
              when this option is not given) is to read the state of the SWP bit and BLK_DEVICE's
              read-only mode and print those values out.

       -v, --verbose
              increase level or verbosity.

       -w, --wr
              when the BLK_DEVICE is in read-only mode, Linux will not typically allow BLK_DEVICE
              to  be  opened read-write by sdparm, so the default action of this script is to use
              the sdparm --readonly option when --set 0 has been invoked.  It  is  possible  that
              BLK_DEVICE  could  be  a  generic  device  (e.g.  /dev/sg3)  which  has a different
              interpretation of the read-only open flag and may fail. For  such  rare  cases  the
              --wr option makes sdparm open BLK_DEVICE read-write when --set 0 is invoked.

EXIT STATUS

       The  exit  status  of this script is 0 when it is successful. Otherwise the exit status is
       that of the sdparm or the blockdev utility, whichever is called last.  See  the  sdparm(8)
       man page.

AUTHORS

       Written by D. Gilbert

COPYRIGHT

       Copyright © 2013 Douglas Gilbert
       This  software  is distributed under a FreeBSD license. There is NO warranty; not even for
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO

       sdparm(sdparm), blockdev(8)