Here is the latest incarnation of this script. Many changes.

#!/usr/bin/perl -w
# Run this perl code from cron every 5 minutes
# Output from 'print' and 'die' will be sent to owner of the cron proc
+ess by cron.

use strict;
use Net::Ping;
use Net::SMTP;

my $private_dir = "/tmp/ping_hosts_dir";

sub check_private_dir { # Used to prevent notify files from being crea
+ted by non-superusers
    unless (-e $private_dir){ mkdir($private_dir, 0700) or die "Can't 
+mkdir $private_dir\n" }
    if (-d $private_dir) {  
        my $mode = (stat($private_dir))[2];
        if (-O $private_dir and ($mode == 040700)) { return }
        elsif (-O $private_dir and ($mode != 040700)) { 
            chmod(0700, $private_dir);
            return;
        }
        else { die "We don't own $private_dir\n" }
    }
    else { die "$private_dir exists and is not a directory\n"; }
}

sub ping_hosts {
    my $ws;
    my $alive;
    my $count;
    my $timeout = 3;
    my @hosts = qw(host1 host2 host3 host4);
    
    # Following uses perl module Net::Ping to prevent spawning externa
+l process 
    my $ping_obj = Net::Ping->new("icmp");
    foreach $ws (@hosts) {
        $alive = 0;
        $count = 5;
        while ($count > 0){
            $alive += $ping_obj->ping($ws, $timeout);
            last if ($alive);
            $count--;
        }
        unless (-e "${private_dir}/${ws}.notify") {
            unless ($alive) {
                print "$ws did not respond to ping\n";
                notify_admins($ws, "is_down");
            }
        }
        elsif ($alive) {
                print "$ws is back up\n";
                notify_admins($ws, "is_up");
        }
        sleep(1); # To prevent flooding
    }
    $ping_obj->close(); # Redundant since open network conn is auto-cl
+osed when leaving sub
}

sub notify_admins { # Called from ping_hosts() with host and changed s
+tatus as arg
    my $ws = shift(@_);
    my $state = shift(@_);
    my $nfile = "${private_dir}/${ws}.notify";
    my @admins = qw(8005551212@page.metrocall.com 8885551212@page.metr
+ocall.com);
    my $message;

    if ( "$state" eq "is_down" ) {
        # Following replaces system(touch $nfile) to prevent spawning 
+external process
        open(NOTIFY, ">>$nfile") or die "Can't create notify file\n";
        close(NOTIFY);
        $message = "$ws does not respond to ping\n";
    }
    else {
        unlink ($nfile);
        $message = "$ws is back up\n";
    }

    # Following replaces forking mailx to prevent spawning external pr
+ocess 
    # Note: Net::SMTP, part of the libnet collection of modules is not
+ part of standard pkg
    my $smtp = Net::SMTP->new('mailhost', HELLO => 'corp.com') or die 
+"Can't connect to mailhost for SMTP\n";
    #$smtp->mail($ENV{USER}.'@corp.com');
    $smtp->mail('root@corp.com');
    $smtp->to(@admins);
    $smtp->data($message);
    $smtp->quit;
}

### MAIN ###
check_private_dir();
# Use $private_dir/hold.notify as a way of disabling notification durr
+ing controlled reboots
ping_hosts() unless (-e "$private_dir/hold.notify");
[download]

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