SG_RESET(8)							     SG3_UTILS							       SG_RESET(8)

NAME

       sg_reset - sends SCSI device, bus or host reset; or checks reset state

SYNOPSIS

       sg_reset [-b] [-d] [-h] [-V] DEVICE

DESCRIPTION

       The  sg_reset  utility with no options (other than DEVICE) reports on the reset state (e.g. if a reset is underway) of DEVICE. When given a
       -d, -b, or -h option it requests a device, bus or host reset respectively.

       In the linux kernel 2.6 series this utility can be called on sd, sr (cd/dvd), st or sg device nodes; if the user  has  appropriate  permis-
       sions.

       In  the	linux  kernel 2.4 series support for this utility first appeared in lk 2.4.19 and could only be called on sg device nodes. Various
       vendors made this capability available in their kernels prior to lk 2.4.19.

OPTIONS

       -b     attempt a SCSI bus reset. This would normally be tried if the device reset (i.e. option -d) was not successful.

       -d     attempt a SCSI device reset. If the device seems stuck, this is the first reset that should be tried. This assumes  the  linux  scsi
	      mid level error handler is not already in the process of resetting DEVICE.

       -h     attempt a host adapter reset. This would normally be tried if both device reset (i.e. option -d) and bus reset (i.e. option -b) were
	      not successful.

       -V     prints the version string then exits.

NOTES

       The error recovery code within the linux kernel when faced with SCSI commands timing out and no response from the device (LU), first  tries
       a  device  reset  and  if  that is not successful tries a bus reset. If that is not successful it tries a host reset. Users of this utility
       should check whether such a recovery is already underway before trying to reset with this utility. The "device,bus,host" order is also rec-
       ommended (i.e. first start with the smallest hammer).

       SAM-4 defines a hard reset (which includes a device power on and a transport reset), a logical unit reset and a I_T nexus reset. A LU reset
       and an I_T nexus reset can be requested via task management function (and support for LU reset is mandatory).  In Linux the SCSI  subsystem
       leaves  it  up  to the low level drivers as to whether a "device reset" is only for the addressed LU or all the LUs in the device that con-
       tains the addressed LU.	The "bus reset" is a transport reset. A "host reset" attempts to re-initialize the HBA	that  the  request  passes
       through on route to the DEVICE. Obviously a "host reset" and a "bus reset" can cause collateral damage.

       This  utility  does  not  allow individual SCSI commands (or tasks as they are called in SAM-4) to be aborted. SAM-4 defines ABORT TASK and
       ABORT TASK SET task management functions for that.

AUTHORS

       Written by Douglas Gilbert.

COPYRIGHT

       Copyright (C) 1999-2006 Douglas Gilbert
       This software is distributed under the GPL version 2. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A  PARTICULAR  PUR-
       POSE.

sg3_utils-1.23							   December 2006						       SG_RESET(8)