DokuWiki » Infrastructure » Operating System » CentOS 6

h1. Install Procedure for ntp-server

h2. Requirements

To install ntpd you will need the following:

* a installed and supported operating system (e.g. CentOS 6.x)

* root-access

* a fast internet connection

h2. Preliminary Note

This procedure is based on a documentation supplied by 

* http://www.cyberciti.biz/faq/rhel-fedora-centos-configure-ntp-client-server/

* http://http://www.gtkdb.de/index_7_576.html

* http://linuxwave.blogspot.com/2007/08/setting-up-your-own-ntp-server.html

h2. Install 

Install ntp:

<pre><code class="bash">

yum install ntp

</code></pre>

h2. Configure ntp Server 

<pre><code class="bash">

vim /etc/ntp.conf

</code></pre>

h3. Use external ntp-Server as reference

Basically the ntp.conf is ready configured, so there is nothing to change

If there is need to use additional or different ntp-server then add it to the @server@ section

h3. Use internal clock as reference

This is only necessary if there is no reliable time-source or ntp-server available at all

<pre><code class="bash">

server 127.127.1.0     # local clock

fudge  127.127.1.0 stratum 4          # set stratum to any value from 0 to 16, the higher the safer, defaults to 10, 4 is working with WinXP and Win7

</code></pre>

h2. Start ntp Server

manually start ntp Server:

<pre><code class="bash">

/etc/init.d/ntpd start

</code></pre>

automatically start the service at boot time:

<pre><code class="bash">

/sbin/service ntpd on

</code></pre>

you can check the runlevels by

<pre><code class="bash">

/sbin/chkconfig --list ntpd

</code></pre>

you should get an output like:

<pre><code class="bash">

ntpd     0:off   1:off   2:off   3:on   4:off   5:on   6:off

</code></pre>

h2. configure firewall

Open NTP Port (123) on Iptables Firewall

<pre><code class="bash">

system-config-firewall-tui

</code></pre>

add port @123:udp@

check if settings are ok

<pre><code class="bash">

cat /etc/sysconfig/iptables

</code></pre>

You should have following line before COMMIT:

<pre><code class="bash">

-A RH-Firewall-1-INPUT -m state --state NEW -p udp --dport 123 -j ACCEPT

</code></pre>

Restart Iptables Firewall:

<pre><code class="bash">

/etc/init.d/iptables restart

</code></pre>

h2. Usage 

try to connect via windows machine and enter as a internet-time-source the ip-adress of the new ntp-server. (e.g. 192.168.2.53)

try to connect via linux machine and use to sync time:

<pre><code class="bash">

ntpdate 192.168.2.53

</code></pre>