USEFUL perl SCRIPT: NTP verifier

Over the years, I have had many problems with NTPd stopping to work
without any notice. That always upset me. I finally wrote a perl
script that checks times among various servers and computes a time
offset for each of them. It can either report that, or it can also set
exit code based on whether all these offsets are below a user
specified limit.

To run it, say query-ntp host1 host2 etc

A good practice is to specify localhost as host1, pool.ntp.org as
host2, and whatever other machines you are checking, would follow
after that.

i
############################################################ ##########
#!/usr/bin/perl

# See Also:
# http://www.webreference.com/programming/perl/ntp/
# http://www.webreference.com/programming/perl/ntp/2.html

#
# Copyright(C) Igor Chudov, 2008.
# Released under GNU Public License version 3.
#

use strict; use warnings;

use Data::Dumper;
use Getopt::Long;
use Net::NTP;
use Time::HiRes qw( time );

my $detail = undef;
my $limit = undef;

GetOptions(
"detail!" => \$detail,
"limit=f" => \$limit,
);

my @servers = @ARGV;

my $bad = undef;

foreach my $server (@servers) {
my $t0 = time;
my %h = get_ntp_response( $server );


#Timestamp Name ID When Generated
#----------------------------------------------------------- -
#Originate Timestamp T1 time request sent by client
#Receive Timestamp T2 time request received by server
#Transmit Timestamp T3 time reply sent by server
#Destination Timestamp T4 time reply received by client
#
#The roundtrip delay d and local clock offset t are defined as
#
#d = (T4 - T1) - (T2 - T3) t = ((T2 - T1) + (T3 - T4)) / 2

my $T1 = $t0; # $h{'Originate Timestamp'};
my $T2 = $h{'Receive Timestamp'};
my $T3 = $h{'Transmit Timestamp'};

my $T4 = time; # From Time::HiRes! Accurate to usec!

#print "T4=$T4\n";
my $d = ($T4 - $T1) - ($T2 - $T3);
my $t = (($T2 - $T1) + ($T3 - $T4)) / 2;
my $duration = $T4-$t0;
my $delta = $T2-$T1 - $duration/2;

if( $limit ) {
if( $delta > $limit || -$delta < -$limit) {
print "Server $server OFF by $delta seconds!!!\n";
$bad = 1;
} else {
print "Server $server OK, delta is $delta seconds!!!\n";
}

} else {
if( $detail ) {
print Dumper( \%h ) . "\nt0=$t0, T4=$T4\ndelay=$d, offset=$t\nelapsed=$duration, delta=$delta\n\n";
} else {
#print "$server delay=$d, offset=$t, delta=$delta, duration=$duration\n";
print sprintf( "%-30s %.5f\n", $server, $t );
}
}
}

exit 1 if $bad;