We are running NTP to keep the clock accurate.

Debian

apt-get install ntp ntp-doc ntp-simple ntpdate

CentOS

yum install ntp

We are using the default configuration that Debian/CentOS ships with. This is primarily a client configuration – we allow other systems only to get the current time; they may not query any further information. (This is limited via the restrict keyword.) The daemon runs primarily in order to sync the system's time with the upstream NTP servers.

The configuration file points to multiple upstream NTP servers within [debian/centos].pool.ntp.org.