#!/usr/local/bin/perl -w
#
# A quick and simple script that will reset a machine if it
# cannot contact the $host for more than 10 minutes. To
# reset the machine, this script will have to be run as
# root.

use Net::Ping;
# this modules is available at: 
# http://www.perl.com/CPAN-local/modules/by-module/Net/
# the current version is Net-Ping-2.02.tar.gz

# host to ping
$host='200.100.50.25';

# where to write error messages
$logFile='/var/log/ping.log';

# seconds to wait between pings
$sleepTime=60;

# maximum ping failures
$maxErrors=10;

# command to run when we reach maximum failures
$theCommand="/sbin/shutdown -r now";

# monitor loop:
$err=0;
logMessage("pingAlive starting");
while (1) {
    # see "man Net::Ping" for more info.
    $p = Net::Ping->new();
    # send a udp ping packet to host, with 10 second timeout
    unless ($p->ping($host, 10)) {
	# ping failed!
	$err++;
	logMessage("Ping ($err) to $host failed");
    } elsif ($err) {
	# regained contact
	logMessage("Successfully reached $host after $err failures");
	$err=0;
    } 
    $p->close();
    
    if ($err >= $maxErrors) {
	logMessage("Too many failures. Taking action: $theCommand");
	system($theCommand);
	$err=0;
    }
    
    sleep $sleepTime;
}

# writes a line to the log file
sub logMessage {
    unless (open F, ">>$logFile") {
	warn "(Note: Cannot write to $logFile)\n";
	open F, ">&STDERR";
    }
    print F scalar(localtime)." ".join(" ",@_)."\n";
    close F;
}