HP-UX Internet Services Administrator's Guide (August 2003)

Configuring NTP
Getting Started with NTP
Chapter 4 57
Getting Started with NTP
The Network Time Protocol (NTP) is a family of programs used to adjust
the system clock on your computer and to synchronize it with external
sources of time. Computers are very sensitive to time deviations caused
by drifting. All clocks drift including the clock inside the computers. NTP
provides accurate time in the range of microsecond to millisecond and
helps overcome drifting.
Some of the pervasive computing processes that may be affected by
disparity in time include: debugging, database and transaction
processing, and compiling software using the make utility.
Debugging system problems becomes difficult if the timestamp in the
system logs are not true.
Databases rely on time to a large extent. Databases and transaction
processing application may get confused if clients and servers have
different times.
The make utility is commonly used to manage the compilation of
software. This utility verifies file timestamps, with one-second
granularity, to decide which .0 files need to be rebuilt when the
underlying source files are changed. The problem increases when files on
machines, at various sites in different time zones, need to be compiled
and built into the new version of the source file. Also, if some directories
are NFS mounted, and the server and client have different notions of the
current time, make can fail to rebuild some derived objects. This can
produce an executable that is not based on the latest sources. A
one-second granularity of file stamp indicates that the client and server
must be synchronized close to 1000 milliseconds, to ensure that make
compiles the appropriate files.
The following topics are discussed in this section:
“NTP Equipment” on page 58
“Choosing the Source of Time” on page 58
“Backup Time Servers” on page 71
“Configuring Your Primary NTP Server” on page 72