Configure NTP

Eucalyptus requires that each machine have the Network Time Protocol (NTP) daemon started and configured to run automatically on reboot.

To use NTP:

Install NTP on the machines that will host Eucalyptus components.
- For CentOS 5, RHEL 5, and RHEL 6, run yum install ntp
- For Ubuntu 10.04 LTS and Ubuntu 12.04 LTS, run apt-get install openntpd
Open the /etc/ntp.conf file (/etc/openntpd/ntpd.conf in Ubuntu) and add NTP servers, as in the following example.
```
server 0.pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org
```
Save and close the file.
Configure NTP to run at reboot. (In Ubuntu, NTP is configured after you install it.)
```
chkconfig ntpd on
```
Start NTP. (In Ubuntu, NTP starts after you install it.)
```
service ntpd start
```
Synchronize your server.
```
ntpdate -u <your_ntp_server>
```
Synchronize your system clock, so that when your system is rebooted, it does not get out of sync.
```
hwclock --systohc
```
Repeat on each host that will run a Eucalyptus component.