Using Signal Handler to timeout an rsh call

[rh0dium]

Hi all,

I don't understand the signal module.  I guess I understand what it
does in principle but I can't figure out how to use it to timeout an
external rsh command after a 5 seconds.  Does anyone know how to do
this.
Here is what I have so far - which is largely based on the example on
the man page..

        def handler(signum, frame):
            print 'Signal handler called with signal', signum
            raise IOError, "Couldn't open device!"


       for host in alive:
            try:
                # Set the signal handler and a 5-second alarm
                signal.signal(signal.SIGALRM, handler)
                signal.alarm(5)

                (out,results) = commands.getstatusoutput( "rsh %s uname
-a" % host)

                signal.alarm(0)          # Disable the alarm
                #self.logger.debug( "%s Connection to %s - %s" %
(out,host,results))

                if out ==256:
                    noaccess.append(host)
                    del alive[host]
                    break
                if out == 0:
                    if  re.search("SunOS",results):
                        hosttype="sun"
                    elif re.search("Linux",results):
                        hosttype="linux"

Can anyone point me in the right direction. Much appreciated!!