======Watchdog on WRAP======

======Introduction======

A hardware watchdog is a highly reliable piece of hardware that has a single function; It resets the hardware system if it has not received a specific input for a specific amount of time. Giving input to the watchdog is called 'petting the watchdog'.

The WRAP board Geode processor has a built-in hardware watchdog.

Typical use of the watchdog is to prevent hard-to-reach standalone systems from crashing (hanging) and becoming useless. Typically, these standalone systems are very reliable and are never looked after; a properly configured Linux system can run unmaintained for years without crashing. However, in the rare case that something does crash, a watchdog might bring the system back alive by rebooting it.

Note that the watchdog does not help to reboot systems that have (gotten) defect hardware.

======Watchdog device driver======

Linux provides a device driver called wd1100:

<code>
voyage:~# lsmod
Module                  Size  Used by
<...>
wd1100                  4560  1
</code>

======Watchdog timeout======

The device driver sets the watchdog timeout. The timeout can be configured as follows:

<code>
root@nehemiah:/etc# cat /etc/modules
<...>
wd1100 sysctl_wd_graceful=0 sysctl_wd_timeout=60
</code>

The device driver (accessible through /dev/watchdog or /dev/wd) must be petted from software within the specified timeout, again and again.

======Watchdog Daemon======

Under (Debian) Linux, a watchdog daemon exists that pets the watchdog, but only if a set of conditions is met.

<code>
root@nehemiah:/etc# ls -al /usr/sbin/watchdog
-rwxr-xr-x  1 root root 76568 May 19  2005 /usr/sbin/watchdog
</code>

The conditions that must be met typically are:
  * temperature within bounds 
  * system load within bounds
  * network reachable
  * memory available
  * ...

======Watchdog Configuration======

The Linux watchdog daemon can be configured to evaluate these conditions on a periodic basis and only pet the watchdog when everything is OK. The default configuration file is /etc/watchdog.conf and an example looks as follows:

<code>
ping                    = 66.249.93.99      # host that must be reachable at all times (www.google.nl)
interface               = eth0              # interface that must receive network traffic
file                    = /etc/checktemp.sh # binary that must always exist
min-memory              = 256               # minimum amount of free memory must be 1 MBytes = 256 * 4kByte page
test-binary             = /etc/checktemp.sh # binary that must always return 0
realtime                = yes               # schedule the watchdog in real-time
priority                = 1                 # high-priority
</code>

For more features, see man watchdog.




=======Temperature Monitoring=======

I have written a small script checktemp.sh that returns 0 if the WRAP board is not too hot:

<code>
#!/bin/bash

TEMP_MAX=44

TEMP_FILE=/sys/bus/i2c/devices/0-0048/temp1_input

if [ ! -f $TEMP_FILE ]; then
  echo "Can not find temperature reading in $TEMP_FILE. Maybe modprobe lm77."
  exit 0
fi

TEMP_MC=`cat $TEMP_FILE`
TEMP=$(($((TEMP_MC + 500)) / 1000))

if [ $TEMP -gt $TEMP_MAX ]; then
  echo '${0} reads a temperature of $TEMP degrees; too hot. Returning -4 (see man watchdog)'
  exit -4
fi

exit 0
</code>

Please review if you like the first 'exit 0', and whether the maximum temperature suits your needs.

* User note: I'm assuming this has something to do with the different wrap hardware but I found my temperature at /sys/bus/i2c/devices/1-0048/temp1_input.

* Alix user note: I don't know how all this works in details, but on my Alix there's a /sys/bus/i2c/devices/xxx/temp1_max, so maybe it would be better to use that value instead of a fixed TEMP_MAX=44. (btw. there's a temp2 as well...check both?).

* Alix sensor is at /sys/bus/i2c/devices/0-004c/temp1_input

====== Final Words ======
  * This was written by Leon Woestenberg, inspired by the [[pxe_voyage|PXE Wiki page by Assaf Gordon]]. I copied parts of his Wiki page formatting.
  * If you find any mistakes, correct them (this is a Wiki, after all).
  * This is free documentation. It is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.
  * Some of the commands in the guide should be executed as ''root'' - **this might damage you system!** \\ Use at your own risk.