| SWWDOG(4) | 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.
 
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 single 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.