Part III. Services / Chapter 28. Time Synchronization with xntp | ||||
|---|---|---|---|---|
 | 27.4. For More Information | 28.2. Setting Up a Local Reference Clock |  | |
Part III. Services / Chapter 28. Time Synchronization with xntp | ||||
|---|---|---|---|---|
| 27.4. For More Information | 28.2. Setting Up a Local Reference Clock | | |
Table of Contents
Abstract
The NTP (Network Time Protocol) mechanism is a protocol for synchronizing the system time over the network. First, a machine can obtain the time from a server that is a reliable time source. Second, a machine can itself act as a time source for other computers in the network. The goal is twofold, maintaining the absolute time and synchronization of the system time of all machines within a network.
Maintaining an exact system time is important in many situations. The built-in hardware (BIOS) clock does often not meet the requirements of applications like databases. Manual correction of the system time would lead to severe problems because, for example, a backward leap can cause malfunction of critical applications. Within a network, it is usually necessary to synchronize the system time of all machines, but manual time adjustment is a bad approach. xntp provides an mechanism to solve these problems. It continuously adjusts the system time with the help of reliable time servers in the network. It further enables the management of local reference clocks, such as radio-controlled clocks.
xntp is preset to use the local computer clock as a time reference.
Using the (BIOS) clock, however, only serves as a fallback
for the case that no time source of greater precision is available.
The easiest way to use a time server in the network is to set
server parameters. For example, if a time server
called ntp.example.com is reachable from the
network, add its name to the file
/etc/ntp.conf by adding the line
server ntp.example.com.
To add more time servers, insert additional lines with the keyword server.
After initializing xntpd with the command
rcxntpd start,
it takes about one hour until the time is stabilized
and the drift file for correcting the local computer clock is created.
With the drift file, the systematic error of the hardware clock
can be computed as soon as the computer is powered on.
The correction is used immediately, resulting in a
higher stability of the system time.
There are two possible ways to use the NTP mechanism as a client: First, the client can query the time from a known server in regular intervals. With many clients, this approach can cause a high load on the server. Second, the client can wait for NTP broadcasts sent out by broadcast time servers in the network. This approach has the disadvantage that the quality of the server is unknown and a server sending out wrong information can cause severe problems.
If the time is obtained via broadcast you do not need the server name.
In this case, enter the line broadcastclient
in the configuration file /etc/ntp.conf.
To use one or more known time servers exclusively,
enter their names in the line starting with servers.
