NetBSD/sbin/wdogctl/wdogctl.8

.\"	$NetBSD: wdogctl.8,v 1.14 2006/08/13 23:23:30 wiz Exp $
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.\" Copyright (c) 2000 Zembu Labs, Inc.
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.\" Author: Jason R. Thorpe <thorpej@zembu.com>
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.Dd August 13, 2006
.Dt WDOGCTL 8
.Os
.Sh NAME
.Nm wdogctl
.Nd Watchdog timer control utility
.Sh SYNOPSIS
.Nm
.Nm
.Fl d
.Nm
.Fl e
.Op Fl A
.Op Fl p Ar seconds
.Ar timer
.Nm
.Fl k
.Op Fl A
.Op Fl p Ar seconds
.Ar timer
.Nm
.Fl t
.Nm
.Fl u
.Op Fl A
.Op Fl p Ar seconds
.Ar timer
.Nm
.Fl x
.Op Fl A
.Op Fl p Ar seconds
.Ar timer
.Sh DESCRIPTION
.Nm
is used to manipulate watchdog timers.
Watchdog timers provide a means of ensuring that a system
continues to make progress.
This is accomplished by use of a timer, provided by either hardware or
software; when the timer expires, the watchdog resets the system.
In this case of a hardware watchdog timer, this is accomplished by
asserting the system's hardware reset signal.
In the case of a software watchdog timer,
this is accomplished by calling the kernel's normal reboot path.
In order to prevent the system from rebooting,
something must refresh the timer to prevent it from expiring.
.Pp
The
.Nx
kernel provides three basic modes in which watchdog timers may
operate: kernel tickle mode, user tickle mode, and external tickle mode.
In kernel tickle mode, a timer in the kernel refreshes the watchdog timer.
In user tickle mode,
.Nm
runs in the background and refreshes the watchdog timer.
In kernel tickle mode, progress of the kernel is ensured.
In user tickle mode, the ability for user programs to run within a known
period of time is ensured.
Note that user tickle mode must be used with caution;
on a heavily loaded system, the timer may
expire accidentally, even though user programs may be making
(very slow) progress.
A user-mode timer is disarmed (if possible) when the device is closed,
unless the timer is activated with the
.Fl x
option.
.Pp
External-mode watchdogs are similar to user-mode watchdogs, except
that the tickle must be done explicitly by a separate invocation of
the program with the
.Fl t
option.
.Pp
In the first two modes, an attempt is made to refresh the watchdog timer
in one half the timer's configured period.
That is, if the watchdog timer has a period of 30 seconds, a refresh attempt
is made every 15 seconds.
.Pp
If called without arguments,
.Nm
will list the timers available on the system.
When arming a watchdog timer, the
.Ar timer
argument is the name of the timer to arm.
.Pp
Only one timer may be armed at a time; if an attempt is made
to arm a timer when one is already armed, an error message
will be displayed and no action will be taken.
.Pp
The options are as follows:
.Bl -tag -offset indent -width XpXperiodXX
.It Fl A
When arming a timer, this flag indicates that an audible alarm is
to sound when the watchdog timer expires and resets the system.
If the selected timer does not support an audible alarm, this
option will be silently ignored.
.It Fl d
This flag disarms the currently active timer.
Note that not all watchdog timers can be disabled once armed.
If the selected timer can not be disabled,
an error message will be displayed and the
timer will remain armed.
.It Fl e
Arm
.Ar timer
in external tickle mode.
.It Fl k
Arm
.Ar timer
in kernel tickle mode.
.It Fl p Ar period
When arming a timer, this flag configures the timer period to
.Ar period
seconds.
If the specified period is outside the timer's range,
an error message will be displayed and no action will be taken.
.It Fl t
This flag tickles an external mode timer.
.It Fl u
Arm
.Ar timer
in user tickle mode.
.It Fl x
Arm
.Ar timer
in a modified user tickle mode: closing the device will not disarm
the timer.
.El
.Sh FILES
.Pa /dev/watchdog
-- the system monitor watchdog timer device
.Sh SEE ALSO
.Xr envsys 4 ,
.Xr envstat 8
.Sh HISTORY
The
.Nm
command first appeared in
.Nx 1.5.1 .
.Sh AUTHORS
The
.Nm
command and the
.Nx
watchdog timer framework were written by
.An Jason R. Thorpe
.Aq thorpej@zembu.com ,
and contributed by Zembu Labs, Inc.