NAME

wd - hardware watchdog timer

SYNOPSIS

­bind -a #w /dev
­/dev/wdctl

DESCRIPTION

This device presents textual information about hardware watchdog timers on PCs and some other machines, and allows user-level control of them.  When enabled, a watchdog timer counts to zero in a few seconds; upon reaching zero, it resets the machine with an NMI or equivalent.  Some process must periodically restart the watchdog to avoid the NMI and keep the system alive; watchdog(8) is one such program.

Reads from ­wdctl yield data of this form:

enabled 3 restarts

or

disabled 3 restarts

Control messages may be written to ­wdctl and include enable, disable, and restart. 

The watchdog is disabled at system shutdown, and when the last open file descriptor for ­wdctl is closed. 

SOURCE

­/sys/src/9/port/devwd.c
­/sys/src/9/∗/∗watchdog.c

SEE ALSO

proc(3), watchdog(8)

BUGS

On PCs, to ensure consistent use of one CPU’s timers, an ­enable message wires the issuing process (see proc(3)) to a CPU, and any subsequent control messages will wire the issuing processes to that same CPU.

Plan 9  —  August 16, 2012