#!/bin/bash
# Synchronize system time from a list of servers
# Install in /etc/cron.hourly or /etc/cron.daily

SERVERLIST[0]="time-a.nist.gov"
SERVERLIST[1]="time-b.nist.gov"
SERVERLIST[2]="time-a.timefreq.bldrdoc.gov"
SERVERLIST[3]="time-b.timefreq.bldrdoc.gov"
SERVERLIST[4]="time-c.timefreq.bldrdoc.gov"
SERVERLIST[5]="utcnist.colorado.edu"
SERVERLIST[6]="time.nist.gov"
SERVERLIST[7]="time-nw.nist.gov"
SERVERLIST[8]="nist1.dc.certifiedtime.com"
SERVERLIST[9]="nist1.datum.com"
SERVERLIST[10]="nist1.nyc.certifiedtime.com"
SERVERLIST[11]="nist1.sjc.certifiedtime.com"
SERVERLIST[12]="north-america.pool.ntp.org"

RDATEBIN=/usr/bin/rdate
HWCLOCKBIN=/sbin/hwclock

COUNTER=0
LASTSERVER=`expr ${#SERVERLIST[@]} - 1`

while ! $RDATEBIN -s ${SERVERLIST[$COUNTER]}
do
        COUNTER=$(($COUNTER + 1));
        echo ${SERVERLIST[$COUNTER]} update failed
        if [ $COUNTER -gt $LASTSERVER ]; then
                exit 1
        fi
done && $HWCLOCKBIN --systohc