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 [--bus] [--device] [--help] [--host] [--no-esc] [--target] [--verbose] [--version] 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 the DEVICE. When given a
       --device, --target, --bus or --host option it requests a device, target, bus or host reset respectively.

       A device reset is applied to the Logical Unit (LU) corresponding to DEVICE. It is most likely implemented by a Low level  Driver  (LLD)	in
       Linux as a LOGICAL UNIT RESET task management function.

       The ability to reset a SCSI target was added in Linux kernel 2.6.27 . A LLD may send Low level Drivers (LLDs) the I_T NEXUS RESET task man-
       agement function. Alternatively it may use a transport mechanism to do the same thing (e.g. a hard reset on the link containing a SAS  tar-
       get).

       In the Linux kernel 2.6 and 3 series this utility can be called on sd, sr (cd/dvd), st or sg device nodes; if the user has appropriate per-
       missions.

       Users of this utility can check whether a reset recovery is already underway before trying to send a new reset with this  utility.  Calling
       this utility with no options, just the DEVICE, will do such a check.

OPTIONS

       -b, --bus
	      attempt  a  SCSI	bus reset. A bus reset is a SCSI Parallel Interface (SPI) concept not found in modern transports. A recent LLD may
	      implement it as a series of resets on targets that might be considered as siblings to the target on the DEVICE path.

       -d, --device
	      attempt a SCSI device reset. This would typically involve sending a LOGICAL UNIT RESET task management function to DEVICE.

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

       -H, --host
	      attempt a host reset. The "host" in this context is often called a Host Bus Adapter (HBA) and contains one or more SCSI initiators.

       -N, --no-esc
	      without this option, if a device reset (--device) fails then it will escalate to a target reset. And if a  target  reset	(--target)
	      fails then it will escalate to a bus reset. And if a bus reset (--bus) fails then it will escalate to a host reset. With this option
	      only the requested reset is attempted. An alternate option name of --no-escalate is also accepted.

       -t, --target
	      attempt a SCSI target reset. A SCSI target contains one or more LUs. This would typically involve sending a  I_T	NEXUS  RESET  task
	      management  function  to	DEVICE There may be a transport action that is equivalent (e.g.  in SAS a hard reset on the link that con-
	      tains the target).

       -v, --verbose
	      increase the degree of verbosity (debug messages).

       -V, --version
	      prints the version string then exits.

NOTES

       The error recovery code within the Linux kernel (SCSI mid-level) when faced with a SCSI command timing out and no response from the  device
       (LU)  does  the	following.  First it 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 successful it tries a host reset. The "device,target,bus,host" order is the  reset  escalation  that  the
       --no-esc option attempts to stop. In large storage configurations the escalation may be (very) undesirable.

       This  utility calls the SG_SCSI_RESET ioctl and as of lk 3.10.7 the --no-esc option is not supported. Patches to implement this functional-
       ity have not been accepted. If you want it, post your concern to linux-scsi@vger.kernel.org which is the linux-scsi list.

       SAM-4 and 5 define 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. LOGICAL UNIT RESET and I_T NEXUS RESET can be requested via task management functions (and
       support for LOGICAL UNIT RESET is mandatory). In Linux the SCSI subsystem leaves it up to the LLDs as to exactly  what  type  (if  any)	of
       reset  is performed.  The "bus reset" is SCSI Parallel Interface (SPI) concept that may not map well to recent SCSI transports so it may be
       a dummy operation. 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 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. And in SAM-4 I_T NEXUS RESET appeared which seems  closely  related:  the
       "I_T" stands for Initiator-Target.

       Transports  may	have  their  own  types of resets not supported by this utility.  For example SAS has a link reset in which both ends of a
       physical link (e.g.  between a SAS expander and a SAS tape drive) renegotiate their connection.

       Prior to version 0.57 of this utility the command line had short options only (e.g. -d but not --device). Also  -h  invoked  a  host  reset
       while  in  the current version -h is equivalent to --help and both -H and --host invoke a host reset. For backward compatibility define the
       environment variable SG3_UTILS_OLD_OPTS or SG_RESET_OLD_OPTS . In this case -h will invoke a host reset and the output will be  verbose	as
       it was previously (equivalent to using the --verbose option now).  For example:

	   SG_RESET_OLD_OPTS=1 sg_reset -h /dev/sg1
       sg_reset: starting host reset
       sg_reset: completed host reset

AUTHORS

       Written by Douglas Gilbert.

COPYRIGHT

       Copyright (C) 1999-2013 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-1.37							    August 2013 						       SG_RESET(8)