Configure basic ntp server and client

Configure ntp server

To configure basic ntp server on centos use following steps:

yum -y install ntp ntpdate ntp-doc
edit /etc/sysconfig/ntpd and change to
```
OPTIONS="-p /var/run/ntpd.pid -g"
```
edit /etc/ntp.conf and add one line for each local network as follows:
```
restrict 192.168.2.0 mask 255.255.255.0 nomodify notrap
```
service ntpd restart
ntpq
1. pe
2. as
  If peers show strata (st) greater than 3 or 4 and associations show reach as no then there must be a firewall issue Please refer to http://superuser.com/questions/141772/what-are-the-iptables-rules-to-permit-ntp for firewall From firewall perspective on server allow
  iptables -A INPUT -p udp --dport 123 -j ACCEPT
  
  iptables -A OUTPUT -p udp --sport 123 -j ACCEPT

Note that setting up ntp server or client on openVZ container will not work. Both ntp server and client must be setup only on base machines

yum -y install ntp ntpdate ntp-doc
edit /etc/sysconfig/ntpd and change to
```
OPTIONS="-p /var/run/ntpd.pid -g"
```
edit /etc/ntp.conf and comment all server lines. Finally add one server line to point to local ntp server
service ntpd restart
ntpq
1. pe
2. as
  If peers show strata (st) greater than 3 or 4 and associations show reach as no then there must be a firewall issue. For firewall refer to http://superuser.com/questions/141772/what-are-the-iptables-rules-to-permit-ntp From firewall perspective on server allow
  iptables -A OUTPUT -p udp --dport 123 -j ACCEPT
  
  iptables -A INPUT -p udp --sport 123 -j ACCEPT

To debug connection to local ntp server you can use: "ntpdate -db <ntp-server>" and see what is going on.