the watchdog is pinged within a certain time, this time is called the
timeout or margin. The simplest way to ping the watchdog is to write
some data to the device. So a very simple watchdog daemon would look
-like this source file: see Documentation/watchdog/src/watchdog-simple.c
+like this:
+
+#include <stdlib.h>
+#include <fcntl.h>
+
+int main(int argc, const char *argv[]) {
+ int fd=open("/dev/watchdog",O_WRONLY);
+ if (fd==-1) {
+ perror("watchdog");
+ exit(1);
+ }
+ while(1) {
+ write(fd, "\0", 1);
+ sleep(10);
+ }
+}
A more advanced driver could for example check that a HTTP server is
still responding before doing the write call to ping the watchdog.
ioctl(fd, WDIOC_GETTIMEOUT, &timeout);
printf("The timeout was is %d seconds\n", timeout);
-Pretimeouts:
-
-Some watchdog timers can be set to have a trigger go off before the
-actual time they will reset the system. This can be done with an NMI,
-interrupt, or other mechanism. This allows Linux to record useful
-information (like panic information and kernel coredumps) before it
-resets.
-
- pretimeout = 10;
- ioctl(fd, WDIOC_SETPRETIMEOUT, &pretimeout);
-
-Note that the pretimeout is the number of seconds before the time
-when the timeout will go off. It is not the number of seconds until
-the pretimeout. So, for instance, if you set the timeout to 60 seconds
-and the pretimeout to 10 seconds, the pretimout will go of in 50
-seconds. Setting a pretimeout to zero disables it.
-
-There is also a get function for getting the pretimeout:
-
- ioctl(fd, WDIOC_GETPRETIMEOUT, &timeout);
- printf("The pretimeout was is %d seconds\n", timeout);
-
-Not all watchdog drivers will support a pretimeout.
-
-Get the number of seconds before reboot:
-
-Some watchdog drivers have the ability to report the remaining time
-before the system will reboot. The WDIOC_GETTIMELEFT is the ioctl
-that returns the number of seconds before reboot.
-
- ioctl(fd, WDIOC_GETTIMELEFT, &timeleft);
- printf("The timeout was is %d seconds\n", timeleft);
-
-Environmental monitoring:
+Envinronmental monitoring:
All watchdog drivers are required return more information about the system,
some do temperature, fan and power level monitoring, some can tell you
WDIOF_SETTIMEOUT Can set/get the timeout
-The watchdog can do pretimeouts.
-
- WDIOF_PRETIMEOUT Pretimeout (in seconds), get/set
-
For those drivers that return any bits set in the option field, the
GETSTATUS and GETBOOTSTATUS ioctls can be used to ask for the current