Mã hóa - ứng dụng này thường sử dụng thời gian như một thành phần của các khóa mã hóa. Quản lý mạng - Ứng dụng này sử dụng thời gian để xác định chính xác khi một cái gì đó đã diễn ra. Đăng nhập - tiện ích syslog sử dụng thời gian để hiển thị các sự kiện hệ thống. Hệ thống tập tin - | Identifying NTP Basics Uses of NTP Many network applications need synchronized clocks to properly function. For example Encryption - This application often uses time as a component of encryption keys. Network management - This application uses time to determine exactly when something took place. Logging - The syslog utility uses time to display system events. File systems - This application timestamps files when they are created or modified. NTP Terms Several terms are used when describing time-related topics. These terms are described in Table 12-1. Table 12-1 NTP Terms Term Description Reference clock A clock that provides current time by accurately following a time standard such as Universal Time Coordinate UTC . Strata NTP servers are arranged in a hierarchy of levels called strata. A stratum-1 server is more accurate than a stratum-10 server. There are 15 strata. Stratum-1 server A highly available NTP server that has its own reference clock. Resolution The smallest increment in time that a clock offers. For example a wristwatch usually has a resolution of one second. Precision The smallest increase in time that a computer program can use. Jitter The difference of the differences experienced when repeatedly measuring time. Accuracy How close a clock follows an official time reference such as UTC. Configuring NTP Copyright 2002 Sun Microsystems Inc. All Rights Reserved. Enterprise Services Revision A 12-3 Identifying NTP Basics Table 12-1 NTP Terms Continued Term Description Reliability The length of time that a clock can remain accurate within a specified range. Wander All clocks suffer from frequency variations. This variation is called wander. Drift file A file that contains the frequency offset of the local system s clock oscillator. Drift file contents can be used by protocols like NTP to cause a system s clock to be more accurate. The default location for Sun s NTP drift file is var ntp . xntpd The NTP daemon. The file A file that causes
