SG_RESET(8)							     SG3_UTILS							       SG_RESET(8)

NAME

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

SYNOPSIS

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

DESCRIPTION

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

       The ability to reset a SCSI target (often called a "hard reset" at the transport level) was added in linux kernel 2.6.27 . Low level  driv-
       ers  that  support  target  reset hopefully reset a logical unit only when given the device reset (i.e. -d) option. This should removed the
       ambiguity of whether "device" meant LU or target that we have had in the past.

       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.

       -t     attempt a SCSI target reset. This assumes the linux scsi mid level error handler is not already in the process of resetting the tar-
	      get that contains the given DEVICE.

       -V     prints the version string then exits.

NOTES

       The error recovery code within the linux kernel when faced with a SCSI command timing out and no response from the device (LU), first tries
       a device reset and if that is not successful tries a target reset. If that is not successful it tries a bus reset. If that is not  success-
       ful  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,target,bus,host" order is also recommended (i.e. first start with the smallest hammer). The above is a  generalization
       and exact details will vary depending on the transport and the low level driver concerned.

       SAM-4  defines  a  hard	reset, a logical unit reset and a I_T nexus reset. A hard reset is defined to be a power on condition, a microcode
       change or a transport reset event. 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 contains the addressed LU (i.e. a target reset). The additional of the  target  reset  (i.e.
       option  -t)  should  give  more	control in this area.  The "bus reset" is a transport reset and may be a dummy operation, depending on the
       transport. A "host reset" attempts to re-initialize the HBA that the request passes through en route to	the  DEVICE.  Note  that  a  "host
       reset" and a "bus reset" may 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.

       Prior to SAM-3 there was a TARGET RESET task management function. Several transports still support that function and many associated  linux
       low level drivers map the -t option to it.

AUTHORS

       Written by Douglas Gilbert.

COPYRIGHT

       Copyright (C) 1999-2009 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-1.28							     July 2009							       SG_RESET(8)