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+Anything that can be automated via a script or a custom program can be added into Xymon. A lot of extension scripts are available for Big Brother at the www.deadcat.net archive, and these will typically work without modifications if you run them in Xymon. Sometimes a few minor tweaks are needed - the Xymon mailing list can help you if you don't know how to go about that.
+But if you have something unique you need to test, writing an extension script is pretty simple. You need to figure out some things:
+  * What name will you use for the column?
+  * How will you test it?
+  * What criteria should decide if the test goes red, yellow or green?
+  * What extra data from the test will you include in the status message ?
+A simple client-side extension script looks like this:
+<code bash>
+#!/bin/sh
+COLUMN=mytest	# Name of the column
+COLOR=green		# By default, everything is OK
+MSG="Bad stuff status"
+# Do whatever you need to test for something
+# As an example, go red if /tmp/badstuff exists.
+if test -f /tmp/badstuff
+   then
+      COLOR=red
+      MSG="${MSG}
+      `cat /tmp/badstuff`
+      "
+   else
+      MSG="${MSG}
+      All is OK
+      "
+   fi
+# Tell Xymon about it
+$BB $BBDISP "status $MACHINE.$COLUMN $COLOR `date`
+${MSG}
+"
+exit 0
+</code>
+You will notice that some environment variables are pre-defined: BB, BBDISP, MACHINE are all provided by Xymon when you run your script via hobbitlaunch. Also note how the MSG variable is used to build the status message - it starts out with just the "Bad stuff status", then you add data to the message when we decided what the status is.
+To run this, save your script in the ~hobbit/client/ext/ directory (i.e. in the ext/ directory off where you installed the Xymon client), then add a new section to the ~hobbit/client/etc/clientlaunch.cfg file like this:
+<code>
+[myscript]
+	ENVFILE $HOBBITCLIENTHOME/etc/hobbitclient.cfg
+	CMD $HOBBITCLIENTHOME/ext/myscript.sh
+	LOGFILE $HOBBITCLIENTHOME/logs/myscript.log
+	INTERVAL 5m
+</code>
+----
+**Server-side scripts** look almost the same, but they will typically use the bbhostgrep utility to pick out hosts in the bb-hosts file that have a special tag defined, and then send one status message for each of those hosts. Like this:
+<code bash>
+#!/bin/sh
+BBHTAG=foo           # What we put in bb-hosts to trigger this test
+COLUMN=$BBHTAG	# Name of the column, often same as tag in bb-hosts
+$BBHOME/bin/bbhostgrep $BBHTAG | while read L
+   do
+      set $L	# To get one line of output from bbhostgrep
+      HOSTIP="$1"
+      MACHINEDOTS="$2"
+      MACHINE=`echo $2 | $SED -e's/\./,/g'`
+      COLOR=green
+      MSG="$BBHTAG status for host $MACHINEDOTS"
+      #... do the test, perhaps modify COLOR and MSG
+      $BB $BBDISP "status $MACHINE.$COLUMN $COLOR `date`
+      ${MSG}
+      "
+   done
+exit 0
+</code>
+:!: Note that for server side tests, you need to loop over the list of hosts found in the bb-hosts file, and send one status message for each host. Other than that, it is just like the client-side tests.