18.4 The Role of the NTP Software

     

The role of the NTP software is to synchronize our system clock with a number of external sources (even if we are a local clock impersonator ). HP currently uses NTP version 3 that is controlled by RFC 1305. NTP version 4 is in development and is a significant change to the standard (RFC 2030). The software is comprised of a number of commands, which we look at later. There are two ways to keep our clock synchronized:

• ntpdate : This is a once-only command and can produce a marked step-change in your system time. Some administrators use this method (I don't know any personally ) via cron job, but many client/server applications are susceptible to marked changes in system time between different parts of the application. Where I do see this command used is at system startup time. We can easily configure NTP to run this command when a system is booted . This brings our system clock into step with our timeserver(s). After that, we can use the xntpd daemon to keep us synchronized.

• xntpd : This daemon is usually started at boot time and keeps our system clock synchronized with a number of timeservers. It will choose the most appropriate timeserver based primarily on the dispersion figure between itself and distant timeservers. The dispersion gives the best indication on the reachability of a particular timeserver.

The main configuration file for NTP is the file /etc/ntp.conf . This specifies the main attributes relating to the selection of timeservers as well as the relationship that our machine has with others in the NTP network. This is where we will spend a significant proportion of our time. First, we must choose our time source.