sg_reset - sends SCSI device, target, bus or host reset; or checks reset state
] [ --no-esc
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
requests a device, target, bus or host reset respectively.
A device reset is applied to the Logical Unit (LU) corresponding to
. 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 management function.
Alternatively it may use a transport mechanism to do the same thing (e.g. a
hard reset on the link containing a SAS target).
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 permissions.
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.
- -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
- -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
- -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 contains the
- -v, --verbose
- increase the degree of verbosity (debug messages).
- -V, --version
- prints the version string then exits.
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
option is not supported. Patches to implement this
functionality may be accepted in lk 3.18 or 3.19 .
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
. 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
but not --device
). Also -h
invoked a host reset
while in the current version -h
is equivalent to --help
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
SG_RESET_OLD_OPTS=1 sg_reset -h /dev/sg1
sg_reset: starting host reset
sg_reset: completed host reset
Written by Douglas Gilbert.
Copyright © 1999-2014 Douglas Gilbert
This software is distributed under the GPL version 2. There is NO warranty; not
even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.