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)