18 Time Services

By:

Stephen Carville

Rev:

12/12/01

18.1 Server Setup

1. Install ntp from RPM or from source code
2. Edit the file /etc/rc.d/init.d/ntpd to add the startup runlevels for chkconfig 
   # chkconfig: 345 55 10
3. Edit the file /etc/ntp/conf to add the servers you will synchronize with. For example:
   server tick.ucla.edu 
   server ns.scruz.net 
   server ntp.ucsd.edu 
   See Section 18.3 for an example file.
4. Start the network time daemon
   # service ntpd start
5. Start ntpq to check if the daemon is working
   # ntpq
6. After a few seconds check ntpd with the command ``peers''. You should see something like:
   remote           refid          st  t when  poll reach  delay offset  jitter  
   ============================================================================ 
   LOCAL(0)         LOCAL(0)       10  l   56    64   377  0.000  0.000  0.000 
   *tick.ucla.edu   .USNO.          1  u  225   512   377 26.351  65.108 9.738  
   +ns.scruz.net    bigben.cac.wash 2  u  254   512   377 22.380  64.081 8.309  
   +bigmama-ucsd-gw time.sdsc.edu  2  u  256   512   377 32.530  53.017 8.902
7. Once the server is verified to be working correctly, add ntp to the boot sequence
   # chkconfig ntpd on 
   # chkconfig ntpd -list 
   ntpd            0:off  1:off  2:off  3:on  4:on  5:on  6:off
8. Hardware clocks drift a lot. After a long uptime, a reboot can leave the system clock off by many hours. To prevent this, reset the hardware clock periodically:
   #!/bin/sh 
    
   # set the hardware clock every day to avoid the problem of  
   # a hard shutdown messing up the time beyond what ntp can fix  
   # easily. Drop this in /etc/cron.daily 
    
   /usr/sbin/setclock

18.1.1 Firewall

Firewalls may need to open port 37/tcp and 37/udp out.

18.2 Client Setup

The simpliest way to synchronize the time on Linux is to use rdate and one of the timeservers. Currently, congo is a timeserver. Create a script in /etc/cron.daily to query the server and set the time:

#! /bin/bash 
# example settime script 
# contact a time server and set the system time  
# requires that timezone be correctly set 
# on linux, drop in /etc/cron.daily 
 
TIMESERVER=congo 
RDATE="/usr/bin/rdate -s" 
 
$RDATE $TIMESERVER

18.3 Example /etc/ntp.conf

# ntp.conf file for a time server syncing to outside sources. 
# 
 
server          127.127.1.                # local clock 
fudge           127.127.1.0       stratum 10 
 
server          tick.ucla.edu 
server          ns.scruz.net 
server          ntp.ucsd.edu 
 
driftfile       /etc/ntp/drift 
broadcast       224.0.1.1 
broadcastdelay  0.008 
 
authenticate    no