Objective 6: Maintain System Time
An accurate system clock is important on a Linux system for a variety of reasons. Timestamps are used for logs. Programs such as make and anacron require accurate modification times on files. The time is used in mail and news headers.
Luckily, there are many ways to keep the time on an Internet-connected Linux system correct. The most popular of these is to use the Network Time Protocol (NTP) and the NTP software package from http://www.ntp.org.
NTP Concepts
The NTP is used to set and synchronize the internal clocks of network-connected systems. When properly configured, systems running the NTP daemon can be synchronized within a few milliseconds (or better), even over relatively slow WAN connections.
The NTP daemon also supports synchronization with an external time source, such as a GPS receiver. Systems directly connected to an external time source (and properly configured) are the most accurate, so they are designated stratum 1 servers. Systems synchronizing to stratum 1 servers are designated stratum 2 and so on down to stratum 15.
Tip
The NTP software package has support for cryptographic key-based authentication, although setting this up is outside the scope of the LPI Level 1 Exams and will not be covered here.
The NTP Software Package Components
The NTP software package consists of several programs, including the NTP daemon and a number of programs used to configure and query NTP servers. The more commonly used programs from the package are ...
Get LPI Linux Certification in a Nutshell, 2nd Edition now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
