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WDOGCTL(8) NetBSD System Manager's Manual WDOGCTL(8)
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wdogctl -- Watchdog timer control utility
wdogctl -e [-A] [-p seconds] timer
wdogctl -k [-A] [-p seconds] timer
wdogctl -u [-A] [-p seconds] timer
wdogctl -x [-A] [-p seconds] timer
wdogctl 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.
The NetBSD 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, wdogctl 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 -x option.
External-mode watchdogs are similar to user-mode watchdogs, except that
the tickle must be done explicitly by a separate invocation of the pro-
gram with the -t option.
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 sec-
If called without arguments, wdogctl will list the timers available on
the system. When arming a watchdog timer, the timer argument is the name
of the timer to arm.
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.
The options are as follows:
-A When arming a timer, this flag indicates that an audi-
ble 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
-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
-e Arm timer in external tickle mode.
-k Arm timer in kernel tickle mode.
-p period When arming a timer, this flag configures the timer
period to period seconds. If the specified period is
outside the timer's range, an error message will be
displayed and no action will be taken.
-t This flag tickles an external mode timer.
-u Arm timer in user tickle mode.
-x Arm timer in a modified user tickle mode: closing the
device will not disarm the timer.
/dev/watchdog -- the system monitor watchdog timer device
acpiwdrt(4), evbarm/iopwdog(4), i386/elansc(4), i386/gcscpcib(4),
i386/geodewdog(4), ipmi(4), itesio(4), pcweasel(4), pwdog(4), swwdog(4),
The wdogctl command first appeared in NetBSD 1.6.
The wdogctl command and the NetBSD watchdog timer framework were written
by Jason R. Thorpe <firstname.lastname@example.org>, and contributed by Zembu Labs,
NetBSD 8.1 August 11, 2011 NetBSD 8.1