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Time Protocol
The Time Protocol is a network protocol in the Internet Protocol Suite. Its purpose is to provide a site-independent, machine readable date and time. The Time Protocol may be implemented over the Transmission Control Protocol (TCP) or the User Datagram Protocol (UDP). A host connects to a server that supports the Time Protocol on port 37. The server then sends the time as a 32-bit unsigned integer in binary format and in network byte order, representing the number of seconds since 00:00 (midnight) 1 January 1900 GMT, and closes the connection. Operation over UDP requires the sending of any datagram to the server port, as there is no connection setup for UDP. The fixed 32-bit data format means that the timestamp rolls over approximately every 136 years, with the first such occurrence on . Programs that use the Time Protocol must be carefully designed to use context-dependent information to distinguish these dates from those in 1900. Many Unix-like operating systems used the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Network Time Protocol
The Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-Network latency, latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use. NTP was designed by David L. Mills of the University of Delaware. NTP is intended to synchronize participating computers to within a few milliseconds of Coordinated Universal Time (UTC). It uses the intersection algorithm, a modified version of Marzullo's algorithm, to select accurate time servers and is designed to mitigate the effects of variable network latency. NTP can usually maintain time to within tens of milliseconds over the public Internet, and can achieve better than one millisecond accuracy in local area networks under ideal conditions. Asymmetric Routing, routes and network congestion can cause errors of 100 ms or more. The protocol is usually described in terms of a client–server model, bu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Internet Protocol Suite
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Protocol (IP). Early versions of this networking model were known as the Department of Defense (DoD) model because the research and development were funded by the United States Department of Defense through DARPA. The Internet protocol suite provides end-to-end data communication specifying how data should be packetized, addressed, transmitted, routed, and received. This functionality is organized into four abstraction layers, which classify all related protocols according to each protocol's scope of networking. An implementation of the layers for a particular application forms a protocol stack. From lowest to highest, the layers are the l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transmission Control Protocol
The Transmission Control Protocol (TCP) is one of the main communications protocol, protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly referred to as TCP/IP. TCP provides reliability (computer networking), reliable, ordered, and error detection and correction, error-checked delivery of a reliable byte stream, stream of octet (computing), octets (bytes) between applications running on hosts communicating via an IP network. Major internet applications such as the World Wide Web, email, remote administration, and file transfer rely on TCP, which is part of the transport layer of the TCP/IP suite. Transport Layer Security, SSL/TLS often runs on top of TCP. TCP is Connection-oriented communication, connection-oriented, meaning that sender and receiver firstly need to establish a connection based on agreed parameters; they do this through three-way Ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
User Datagram Protocol
In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in Network packet, packets) to other hosts on an Internet Protocol (IP) network. Within an IP network, UDP does not require prior communication to set up communication channels or data paths. UDP is a connectionless protocol, meaning that messages are sent without negotiating a connection and that UDP does not keep track of what it has sent. UDP provides checksums for data integrity, and port numbers for addressing different functions at the source and destination of the datagram. It has no Handshake (computing), handshaking dialogues and thus exposes the user's program to any Reliability (computer networking), unreliability of the underlying network; there is no guarantee of delivery, ordering, or duplicate protection. If error-correction facilities are needed at the network interface level, an applica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Network Byte Order
'' Jonathan_Swift.html" ;"title="Gulliver's Travels'' by Jonathan Swift">Gulliver's Travels'' by Jonathan Swift, the novel from which the term was coined In computing, endianness is the order in which bytes within a word (data type), word of digital data are transmitted over a data communication medium or Memory_address, addressed (by rising addresses) in computer memory, counting only byte significance compared to earliness. Endianness is primarily expressed as big-endian (BE) or little-endian (LE), terms introduced by Danny Cohen into computer science for data ordering in an Internet Experiment Note published in 1980. Also published at The adjective ''endian'' has its origin in the writings of 18th century Anglo-Irish writer Jonathan Swift. In the 1726 novel ''Gulliver's Travels'', he portrays the conflict between sects of Lilliputians divided into those breaking the shell of a boiled egg from the big end or from the little end. By analogy, a CPU may read a digital word b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix-like
A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-like Application software, application is one that behaves like the corresponding List of POSIX commands, Unix command or Unix shell, shell. Although there are general Unix philosophy, philosophies for Unix design, there is no technical standard defining the term, and opinions can differ about the degree to which a particular operating system or application is Unix-like. Some well-known examples of Unix-like operating systems include Linux, FreeBSD and OpenBSD. These systems are often used on servers as well as on personal computers and other devices. Many popular applications, such as the Apache HTTP Server, Apache web server and the Bash (Unix shell), Bash shell, are also designed to be used on Unix-like systems. Definition The Open ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rdate
On Unix-like operating systems, rdate is a tool for querying the current time from a network server and, optionally, setting the system time. Rdate uses the Time Protocol. The Time Protocol is generally considered obsolete and has been replaced by the Network Time Protocol (NTP). When used to set the local system time, rdate operates by changing system time immediately to the time and date returned by the server. Abrupt changes of clock settings have been found to cause problems for software relying on timing. This led to the development of the Network Time Protocol, which gradually changes the system time and does not skip ticks. Due to the problems described above, rdate is generally used only on systems where NTP is not available, or in specialized circumstances where it is required that system time be set correctly as soon as possible during initial setup, before services which may be vulnerable to abrupt time-changes have started. See also * ntpd The Network Time Proto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ntpdate
ntpdate is a computer program used to quickly synchronize and set computers' date and time by querying a Network Time Protocol (NTP) server. It is available for a wide variety of unix-like operating systems. The accuracy and reliability of ntpdate entirely depends on the accuracy and network link stability of the first server it connects with. As this inaccuracy can lead to a multitude of problems, the maintainers have decided to deprecate it in favor of only using the ntpd (network time protocol daemon) or a sntp (simple network time protocol) query. See also * timesyncd systemd is a software suite that provides an array of system components for Linux operating systems. The main aim is to unify service configuration and behavior across Linux distributions. Its primary component is a "system and service manage ... References External links NTP.org — Home page of the Network Time Protocol Network time-related software {{compu-prog-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inetd
inetd (internet service daemon) is a super-server Daemon (computer software), daemon on many Unix systems that provides Internet services. For each configured service, it listens for requests from connecting clients. Requests are served by spawning a process which runs the appropriate executable, but simple services such as ''echo'' are served by inetd itself. External executables, which are run on request, can be single- or multi-threaded. First appearing in BSD, 4.3BSD, it is generally located at /usr/sbin/inetd. inetd is based on the (service) activator pattern Function Often called a super-server, inetd listens on designated TCP and UDP port, ports used by Internet services such as File Transfer Protocol, FTP, POP3, and telnet. When a Transmission Control Protocol, TCP packet or User Datagram Protocol, UDP packet arrives with a particular destination port number, inetd launches the appropriate server program to handle the connection. For services that are not expected to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xinetd
In computer networking, xinetd (''Extended Internet Service Daemon'') is an open-source software, open-source super-server Daemon (computer software), daemon which runs on many Unix-like operating system, systems, and manages Internet-based connectivity. It offers a more secure alternative to the older inetd ("the Internet daemon"), which most modern Linux distributions have deprecated. Description xinetd listens for incoming requests over a network and launches the appropriate Network service, service for that request. Requests are made using port numbers as identifiers and xinetd usually launches another Daemon (computing), daemon to handle the request. It can be used to start services with both privileged and non-privileged port numbers. xinetd features access control mechanisms such as TCP Wrapper Access control list, ACLs, extensive data logging, logging capabilities, and the ability to make Service (systems architecture), services available based on time. It can place ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Daemon (computer Software)
In computing, a daemon is a program that runs as a background process, rather than being under the direct control of an interactive user. Customary convention is to name a daemon process with the letter ''d'' as a suffix to indicate that it's a daemon. For example, is a daemon that implements system logging facility, and is a daemon that serves incoming SSH connections. Even though the concept can apply to many computing systems, the term ''daemon'' is used almost exclusively in the context of Unix-based systems. In other contexts, different terms are used for the same concept. Systems often start daemons at boot time that will respond to network requests, hardware activity, or other programs by performing some task. Daemons such as cron may also perform defined tasks at scheduled times. Terminology In the context of computing, the word is generally pronounced either as or . The term was coined by the programmers at MIT's Project MAC. According to Fernando J. Corbat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
