SWWDOG(4) BSD Kernel Interfaces Manual SWWDOG(4)NAME
swwdog -- software watchdog timer
SYNOPSIS
pseudo-device swwdog
DESCRIPTION
The swwdog driver provides a software watchdog timer that works with wdogctl(8). If the timer expires, the system reboots if the boolean
variable swwdog_reboot is true; otherwise, the system will panic. swwdog_reboot is accessible as a sysctl(8) variable, hw.swwdog.reboot and
defaults to false.
The default period of swwdog is 60 seconds.
As with other watchdog timers, the swwdog driver prevents a system from suspending when the watchdog is armed.
SEE ALSO sysctl(8), wdogctl(8)HISTORY
The swwdog driver was written by Steven M. Bellovin.
BUGS
Only one watchdog timer can be active at any given time. (Arguably, this is a bug in the watchdog timer framework.) Therefore, only a sin-
gle instance of the swwdog device can be created.
Kernel tickle mode is useless with swwdog and arguably should be rejected, since both it and this driver rely on the same callout mechanism;
if one is blocked, almost certainly the other is as well.
The alarm option to wdogctl(8) isn't implemented.
BSD June 8, 2011 BSD
Check Out this Related Man Page
WDOGCTL(8) BSD System Manager's Manual WDOGCTL(8)NAME
wdogctl -- Watchdog timer control utility
SYNOPSIS
wdogctl
wdogctl -d
wdogctl -e [-A] [-p seconds] timer
wdogctl -k [-A] [-p seconds] timer
wdogctl -t
wdogctl -u [-A] [-p seconds] timer
wdogctl -x [-A] [-p seconds] timer
DESCRIPTION
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
program 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 seconds.
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 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.
-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.
-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.
FILES
/dev/watchdog -- the system monitor watchdog timer device
SEE ALSO acpiwdrt(4), evbarm/iopwdog(4), i386/elansc(4), i386/gcscpcib(4), i386/geodewdog(4), ipmi(4), itesio(4), pcweasel(4), pwdog(4), swwdog(4),
x86/ichlpcib(4)HISTORY
The wdogctl command first appeared in NetBSD 1.6.
AUTHORS
The wdogctl command and the NetBSD watchdog timer framework were written by Jason R. Thorpe <thorpej@zembu.com>, and contributed by Zembu
Labs, Inc.
BSD August 11, 2011 BSD