linux related concepts
Time-related
Blog
Time on CENTOS / time zone setting
Linux basis: timedatectl commands documented
network protocol: NTP: 1: Network Time Protocol based
network protocol: NTP: 2: Use NTPD structures NTP server
network protocols: NTP: 3: Use Chrony structures NTP server
NTP Network Time Protocol
The acronym NTP (Network Time Protocol) Network Time Protocol, which is the protocol used to time synchronize each computer on the network.
Why NTP protocol
- Time for each computer on the network is not synchronized
with a sync for many reasons, such as manually modified time operating system, such as a CMOS cell reset, etc. due to the reset time. - Time each computer on the network is not accurate
clocks that we use, the accuracy of certain errors generally higher accuracy will reach an average of about a minute error per year, although not substantially affect everyday use, but in the computer this world has cause problems.
What is accurate
Atomic clock is the world's most accurate timing tool, it appeared in the 1950s, the use of the yard do-or release of electromagnetic energy is emitted to time, very stable, coupled with a series of precision control instruments, can reach 2000 thousand to one second error, the accuracy can be achieved substantially all current requirements.
When GMT GMT
GMT (Greenwich Mean Time, GMT) refers to standard time on the outskirts of London's Royal Greenwich Observatory, because the prime meridian is defined by where the warp. Theoretically, noon Greenwich Mean Time refers to the time when the sun crosses the Greenwich meridian. As the Earth in its velocity unevenness elliptical orbit, this time may vary and the actual sun 16 minutes. Earth's daily rotation is somewhat irregular, but is slowly decelerating. So, GMT is no longer used as a standard time, GMT time is erroneous. .
UTC Coordinated Universal Time
Coordinated Universal Time Coordinated Universal Time, also known as the unified world time, Universal Time, Coordinated Universal Time.
UTC is characterized by high precision, tens of thousands of years before the error 1 second.
RTC system hardware time
RTC Real-Time Clock (Real-Time Clock), system hardware clock,
the system clock is divided into hardware and software clocks.
- When the system is shut down, the clock can not run the software, hardware clock can be normal time,
- At system startup, the software reads the time from the hardware, the software as the initial time
- System shutdown, software is written to the system time to time.
File system-related
NFS
NFS (Network File System) that is a network file system, FreeBSD is a supported file system, which allows sharing of resources between computers on the network. In the application of the NFS, the NFS client's local application can transparently read and write files located on a remote NFS server, just like access local files.
ftp file transfer protocol
File Transfer Protocol (English: File Transfer Protocol, abbreviation: FTP) is a standard protocol for file transfer over the network, using a client / server model. It belongs to the application layer of the network transmission protocol. The difference between the file transfer (file transfer), and file access (file access): the former is provided by the FTP, which is provided by the application systems such as NFS, etc.