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Dup (system Call)
In Unix-like operating systems, (short for "duplicate") and system calls create a copy of a given file descriptor. This new descriptor actually does not behave like a copy, but like an alias of the old one. C library POSIX definition The dup and dup2 calls are standardized by the POSIX specification. Similar(following the logic) to pointers, the new file description is merely an alias to the old one, with both file descriptors being capable of being used interchangeably. Both file descriptors in a dup() system call refer to the same open file description which means they share file offset and file status flags; Similar but not identical to the logic used in pointers, shallow or deep copying or references, changes to the offset on one of the file descriptors changes it for the other file descriptor. When using dup(), the two file descriptors don't share the same file descriptor flags. In the calling process the lowest numbered unused file descriptor will be used for the new f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix-like
A Unix-like (sometimes referred to as UN*X 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 is one that behaves like the corresponding Unix command or shell. Although there are general 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 and BSD. These systems are often used on servers, as well as on personal computers and other devices. Many popular applications, such as the Apache web server and the Bash shell, are also designed to be used on Unix-like systems. One of the key features of Unix-like systems is their ability to support multiple users and processes simultaneously. This allows users to run multipl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linux Kernel
The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU operating system, which was written to be a free (libre) replacement for Unix. Linux is provided under the GNU General Public License version 2 only, but it contains files under other compatible licenses. Since the late 1990s, it has been included as part of a large number of operating system distributions, many of which are commonly also called Linux. Linux is deployed on a wide variety of computing systems, such as embedded devices, mobile devices (including its use in the Android operating system), personal computers, servers, mainframes, and supercomputers. It can be tailored for specific architectures and for several usage scenarios using a family of simple commands (that is, without the need of manually editing its source code ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix Pipe
In Unix-like computer operating systems, a pipeline is a mechanism for inter-process communication using message passing. A pipeline is a set of processes chained together by their standard streams, so that the output text of each process (''stdout'') is passed directly as input (''stdin'') to the next one. The second process is started as the first process is still executing, and they are executed concurrently. The concept of pipelines was championed by Douglas McIlroy at Unix's ancestral home of Bell Labs, during the development of Unix, shaping its toolbox philosophy. It is named by analogy to a physical pipeline. A key feature of these pipelines is their "hiding of internals" (Ritchie & Thompson, 1974). This in turn allows for more clarity and simplicity in the system. This article is about anonymous pipes, where data written by one process is buffered by the operating system until it is read by the next process, and this uni-directional channel disappears when the processes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pipe (system Call)
In computer science, an anonymous pipe is a simplex FIFO communication channel that may be used for one-way interprocess communication (IPC). An implementation is often integrated into the operating system's file IO subsystem. Typically a parent program opens anonymous pipes, and creates a new process that inherits the other ends of the pipes, or creates several new processes and arranges them in a pipeline. Full-duplex (two-way) communication normally requires two anonymous pipes. Pipelines are supported in most popular operating systems, from Unix and DOS onwards, and are created using the ", " character in many shells. Unix Pipelines are an important part of many traditional Unix applications and support for them is well integrated into most Unix-like operating systems. Pipes are created using the pipe system call, which creates a new pipe and returns a pair of file descriptors referring to the read and write ends of the pipe. Many traditional Unix programs are desig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redirection (computing)
In computing, redirection is a form of interprocess communication, and is a function common to most command-line interpreters, including the various Unix shells that can redirect standard streams to user-specified locations. In Unix-like operating systems, programs do redirection with the system call, or its less-flexible but higher-level stdio analogues, and . Redirecting standard input and standard output Redirection is usually implemented by placing certain characters between commands. Basic Typically, the syntax of these characters is as follows, using < to redirect input, and > to redirect output. command > file1 executes , placing the output in , as opposed to displaying it at the terminal, which is the usual destination for standard output. This will clobber any existing data in . Using command > file1. To read from a stream literal (an inline file, passed to the standard input), one can use a here document, using the << operator: $ tr a-z A-Z uno dos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix Shell
A Unix shell is a command-line Interpreter (computing), interpreter or shell (computing), shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating system to control the execution of the system using shell scripts. Users typically interact with a Unix shell using a terminal emulator; however, direct operation via serial hardware connections or Secure Shell are common for server systems. All Unix shells provide filename Wildcard character, wildcarding, Pipeline (Unix), piping, here documents, command substitution, Variable (programming), variables and control flow, control structures for Conditional (programming), condition-testing and iteration. Concept Generally, a ''shell'' is a program that executes other programs in response to text commands. A sophisticated shell can also change the environment in which other programs execute by passing environm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Close (system Call)
A close system call is a system call used to close a file descriptor by the kernel. For most file systems, a program terminates access to a file in a filesystem using the close system call. This flushes file buffers, updates file metadata, which may include and end-of-file indicator in the data; de-allocates resources associated with the file (including the file descriptor) and updates the system wide table of files in use. Some programming languages maintain a data structure of files opened by their runtime library and may close when the program terminates. This practice is known as resource acquisition is initialization (RAII). Some operating systems will invoke the close on files held by a program if it terminates. Some operating systems will invoke the close syscall as part of an operating system recovery as a result of a system failure. C library POSIX definition Theclosecall is standardized by the POSIX specification int close (int filedes); int fclose (FILE *strea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fcntl
In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier (Handle (computing), handle) for a file (computing), file or other input/output System resource, resource, such as a pipe (Unix), pipe or network socket. File descriptors typically have non-negative Integer (computer science), integer values, with negative values being reserved to indicate "no value" or error conditions. File descriptors are a part of the POSIX application programming interface, API. Each Unix process (computing), process (except perhaps daemon (computer software), daemons) should have three standard POSIX file descriptors, corresponding to the three standard streams: Overview In the traditional implementation of Unix, file descriptors index into a per-process maintained by the kernel, that in turn indexes into a system-wide table of files opened by all processes, called the . This table records the ''mode'' with which the file (or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Open (system Call)
For most file systems, a program initializes access to a file in a file system using the open system call. This allocates resources associated to the file (the file descriptor), and returns a handle that the process will use to refer to that file. In some cases the open is performed by the first access. The same file may be opened simultaneously by several processes, and even by the same process, resulting in several file descriptors for the same file; depending on the file organization and filesystem. Operations on the descriptors such as moving the file pointer or closing it are independentthey do not affect other descriptors for the same file. Operations on the file, such as a write, can be seen by operations on the other descriptors: a later read can read the newly written data. During the open, the filesystem may allocate memory for buffers, or it may wait until the first operation. The absolute file path is resolved. This may include connecting to a remote host and n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which includes the kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name "GNU/Linux" to emphasize the importance of GNU software, causing some controversy. Popular Linux distributions include Debian, Fedora Linux, and Ubuntu, the latter of which itself consists of many different distributions and modifications, including Lubuntu and Xubuntu. Commercial distributions include Red Hat Enterprise Linux and SUSE Linux Enterprise. Desktop Linux distributions include a windowing system such as X11 or Wayland, and a desktop environment such as GNOME or KDE Plasma. Distributions intended for ser ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
System Call
In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, accessing a hard disk drive or accessing the device's camera), creation and execution of new processes, and communication with integral kernel services such as process scheduling. System calls provide an essential interface between a process and the operating system. In most systems, system calls can only be made from userspace processes, while in some systems, OS/360 and successors for example, privileged system code also issues system calls. Privileges The architecture of most modern processors, with the exception of some embedded systems, involves a security model. For example, the ''rings'' model specifies multiple privilege levels under which software may be executed: a program is usually limited to its own address space so that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Functions (programming)
In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Functions may be defined within programs, or separately in libraries that can be used by many programs. In different programming languages, a function may be called a routine, subprogram, subroutine, method, or procedure. Technically, these terms all have different definitions, and the nomenclature varies from language to language. The generic umbrella term ''callable unit'' is sometimes used. A function is often coded so that it can be started several times and from several places during one execution of the program, including from other functions, and then branch back (''return'') to the next instruction after the ''call'', once the function's task is done. The idea of a subroutine was initially conceived by John Mauchly during his work on ENIAC, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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