HP-UX Internet Services Administrator's Guide (May 2010)

4 Configuring NTP
The Network Time Protocol (NTP) assures accurate synchronization of the computer’s
clock time with reference to a number of primary reference sources, using an equipment
such as a radio receiver. NTP runs as a continuous background client process on a
system, and sends periodic time requests to primary servers to obtain the time stamps.
It also checks for errors caused due to equipment or propagation failures.
This chapter describes the basic and advanced NTP concepts, components and
configuration instructions required to use NTP. This chapter also includes
troubleshooting information.
This chapter contains the following topics:
• “Getting Started with NTP” (page 45)
• “Advanced NTP Topics” (page 58)
• “Troubleshooting NTP” (page 70)
The section Getting Started with NTP is ideal for beginners with limited experience on
NTP. The section Advanced NTP Topics is ideal for anexperienced user with sufficient
experience on NTP.
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
Getting Started with NTP 45