1SG_RESET(8) SG3_UTILS SG_RESET(8)
2
6 sg_reset - sends SCSI device, target, bus or host reset; or checks
7 reset state
8
10 sg_reset [--bus] [--device] [--help] [--host] [--no-esc] [--target]
11 [--verbose] [--version] DEVICE
12
14 The sg_reset utility with no options (just a DEVICE) reports on the
15 reset state (e.g. if a reset is underway) of the DEVICE. When given a
16 --device, --target, --bus or --host option it requests a device, tar‐
17 get, bus or host reset respectively.
18 A device reset is applied to the Logical Unit (LU) corresponding to
20 DEVICE. It is most likely implemented by a Low level Driver (LLD) in
21 Linux as a LOGICAL UNIT RESET task management function.
22 The ability to reset a SCSI target was added in Linux kernel 2.6.27 . A
24 LLD may send Low level Drivers (LLDs) the I_T NEXUS RESET task manage‐
25 ment function. Alternatively it may use a transport mechanism to do the
26 same thing (e.g. a hard reset on the link containing a SAS target).
27 In the Linux kernel 2.6 and 3 series this utility can be called on sd,
29 sr (cd/dvd), st or sg device nodes; if the user has appropriate permis‐
30 sions.
31 Users of this utility can check whether a reset recovery is already
33 underway before trying to send a new reset with this utility. Calling
34 this utility with no options, just the DEVICE, will do such a check.
35
37 -b, --bus
38 attempt a SCSI bus reset. A bus reset is a SCSI Parallel Inter‐
39 face (SPI) concept not found in modern transports. A recent LLD
40 may implement it as a series of resets on targets that might be
41 considered as siblings to the target on the DEVICE path.
42 -d, --device
44 attempt a SCSI device reset. This would typically involve send‐
45 ing a LOGICAL UNIT RESET task management function to DEVICE.
46 -h, --help
48 print the usage message then exit.
49 -H, --host
51 attempt a host reset. The "host" in this context is often called
52 a Host Bus Adapter (HBA) and contains one or more SCSI initia‐
53 tors.
54 -N, --no-esc
56 without this option, if a device reset (--device) fails then it
57 will escalate to a target reset. And if a target reset (--tar‐
58 get) fails then it will escalate to a bus reset. And if a bus
59 reset (--bus) fails then it will escalate to a host reset. With
60 this option only the requested reset is attempted. An alternate
61 option name of --no-escalate is also accepted.
62 -t, --target
64 attempt a SCSI target reset. A SCSI target contains one or more
65 LUs. This would typically involve sending a I_T NEXUS RESET task
66 management function to DEVICE There may be a transport action
67 that is equivalent (e.g. in SAS a hard reset on the link that
68 contains the target).
69 -v, --verbose
71 increase the degree of verbosity (debug messages).
72 -V, --version
74 prints the version string then exits.
75
77 The error recovery code within the Linux kernel (SCSI mid-level) when
78 faced with a SCSI command timing out and no response from the device
79 (LU) does the following. First it tries a device reset and if that is
80 not successful tries a target reset. If that is not successful it tries
81 a bus reset. If that is not successful it tries a host reset. The
82 "device,target,bus,host" order is the reset escalation that the --no-
83 esc option attempts to stop. In large storage configurations the esca‐
84 lation may be (very) undesirable.
85 This utility calls the SG_SCSI_RESET ioctl and as of lk 3.10.7 the
87 --no-esc option is not supported. Patches to implement this functional‐
88 ity may be accepted in lk 3.18 or 3.19 .
89 SAM-4 and 5 define a hard reset, a LOGICAL UNIT RESET and a I_T NEXUS
91 RESET. A hard reset is defined to be a power on condition, a microcode
92 change or a transport reset event. LOGICAL UNIT RESET and I_T NEXUS
93 RESET can be requested via task management functions (and support for
94 LOGICAL UNIT RESET is mandatory). In Linux the SCSI subsystem leaves it
95 up to the LLDs as to exactly what type (if any) of reset is performed.
96 The "bus reset" is SCSI Parallel Interface (SPI) concept that may not
97 map well to recent SCSI transports so it may be a dummy operation. A
98 "host reset" attempts to re-initialize the HBA that the request passes
99 through en route to the DEVICE. Note that a "host reset" and a "bus
100 reset" may cause collateral damage.
101 This utility does not allow individual SCSI commands to be aborted.
103 SAM-4 defines ABORT TASK and ABORT TASK SET task management functions
104 for that.
105 Prior to SAM-3 there was a TARGET RESET task management function. And
107 in SAM-4 I_T NEXUS RESET appeared which seems closely related: the
108 "I_T" stands for Initiator-Target.
109 Transports may have their own types of resets not supported by this
111 utility. For example SAS has a link reset in which both ends of a
112 physical link (e.g. between a SAS expander and a SAS tape drive) rene‐
113 gotiate their connection.
114 Prior to version 0.57 of this utility the command line had short
116 options only (e.g. -d but not --device). Also -h invoked a host reset
117 while in the current version -h is equivalent to --help and both -H and
118 --host invoke a host reset. For backward compatibility define the envi‐
119 ronment variable SG3_UTILS_OLD_OPTS or SG_RESET_OLD_OPTS . In this case
120 -h will invoke a host reset and the output will be verbose as it was
121 previously (equivalent to using the --verbose option now). For exam‐
122 ple:
123 SG_RESET_OLD_OPTS=1 sg_reset -h /dev/sg1
125 sg_reset: starting host reset
126 sg_reset: completed host reset
127
129 Written by Douglas Gilbert.
130
132 Copyright © 1999-2014 Douglas Gilbert
133 This software is distributed under the GPL version 2. There is NO war‐
134 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
135 POSE.
136sg3_utils-1.40 October 2014 SG_RESET(8)