. 
ntp is the Network Time Protocol suite.
Installing ntpd
First, make sure ntp/ntpdate are installed. The package is by default installed on Mandrake Linux and Redhat.
If you do not have ntp installed you will find packages on your distributions install-cd(s).
On Gentoo Linux, install by typing
--- emerge ntp
Configuration files for running ntp as daemon
ntpd manpage
Client Setup
Now, edit the following files:
--- /etc/ntp.conf
The only important thing is that the line contains server some.thing.org.
Example:
---
server ntp.uio.no
driftfile /etc/ntp/drift
broadcastdelay 0.008
authenticate no
---
Make sure you add ntpd as a boot (init) service.
Gentoo Linux: `rc-update add ntpd default` , `/etc/init.d/ntpd start`
(LAN) Server setup
To run a ntp server to sync the clocks on your lan, edit
--- /etc/ntp.conf
Example:
---
server fartein.ifi.uio.no prefer
server ntp.uio.no
server ntp.eunet.no
fudge 10.0.0.50 stratum 10
driftfile /etc/ntp/drift
broadcastdelay 0.008
authenticate no
---
fudge tells the server to pass on the correct time to the given network interface. stratum is the level of time servers, 10 being the lowest. You only need a higher number if you will be acting as a public internet timeserver with fast bandwidth.
It makes sence to add a few servers. Select the best as prefer
Make sure you add ntpd as a boot (init) service.
Gentoo Linux: `rc-update add ntpd default` , `/etc/init.d/ntpd start`
Firewalls
ntp uses port 123, both UDP and TCP. Make sure this port is not blocked by a firewall.
If you are using iptables, you can open this port with
--- $IPTABLES -A INPUT -j ACCEPT -p tcp --dport 123
Known valid and working ntp servers
| server adress |
Location |
| ntp.ipv6.viagenie.qc.ca |
IPV6 ONLY |
| clock.via.net |
|
| server fartein.ifi.uio.no |
Norway |
| server ntp.uio.no |
Norway |
| server ntp.eunet.no |
Norway |
| ntp.demon.co.uk |
UK |
| ntp.nasa.gov |
USA |
| bigben.cac.washington.edu |
USA |
| time-b.nist.gov |
USA |
| montpelier.ilan.caltech.edu |
USA |
| nist1.aol-ca.truetime.com |
USA |
| nist1.datum.com |
USA |
| time-a.timefreq.bldrdoc.gov |
USA |
| time-b.timefreq.bldrdoc.gov |
USA |
| time-c.timefreq.bldrdoc.gov |
USA |
| time.nist.gov |
USA |
| utcnist.colorado.edu |
USA |
| tick.usno.navy.mil |
USA |
| tock.usno.navy.mil |
USA |
| mizbeaver.udel.edu |
USA |
Server List
Setting the clock at boot or using cron
I good idea is _not_ to run the ntpd daemon on clients as it uses about 1,7 MB memory, unless you are a server or have a box with a broken clock. Many boxes clocks do drift along on their own, a check every hour or day is generally a good idea.
rdate
rdate is a simple 3 kB tool for syncing the system clock to a server. It's options are `-p` to print the date on the given server, `-s` to set the system clock according to it (must be done as root) and `-u` to use the UDP protocol. Example:
`rdate -p sntp.lth.se`
rdate manual page
clockspeed
clockspeed is a very small tool for setting the clock and is, for clients, a much better alternative than installing the 4+ MB ntp package.
cron & ntp
You can simply add ntpdate as a cron job every now and then:
--- echo 'ntpdate -b server.dot.com' > /etc/cron.hourly/time.cron
--- chmod a+x /etc/cron.hourly/time.cron
Most distributions come with a cron. dcron and Vixie cron are nice.
Gentoo & ntp-client
You can set the clock using ntp at boot (without starting the daemon) on Gentoo Linux by editing:
--- /etc/conf.d/ntp-client
The file should contain:
---
NTPDATE_CMD="ntpdate"
NTPDATE_OPTS="-b your.server.here"
---
Then add ntp-client to the services started at boot:
--- rc-update add ntp-client default
You can check what services are started at boot with `rc-status`.
Page source:
Copyright (c) 2000-2004 Øyvind Sæther. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".
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