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Unix File Types
The Unix file types are the categories of file formats that a Unix-based system uses to provide context-sensitive behavior of file system items all of which called ''files'' in Unix-based systems. POSIX defines categories: regular, Directory (computing), directory, symbolic link, Named pipe, FIFO special, Device file, block special, character special, and Unix domain socket, socket. An operating system may define additional categories (e.g. Solaris Doors (computing), doors). A regular file is any file format that the file system does not know and relies on applications to manipulate. The other categories are for file formats that the file system inherently knows and can manipulate. The ls, ls -l command reports a file's category via the character before the File-system permissions#Notation of traditional Unix permissions, permissions information. The File (command), file command reports file format information; even for regular files. Representations Numeric The type of a f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File Format
A file format is a Computer standard, standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary format, proprietary or open format, open. Some file formats are designed for very particular types of data: Portable Network Graphics, PNG files, for example, store Raster graphics, bitmapped Graphics file format, images using lossless data compression. Other file formats, however, are designed for storage of several different types of data: the Ogg format can act as a container format (digital), container for different types of multimedia including any combination of sound, audio and video, with or without text (such as subtitles), and metadata. A text file can contain any stream of characters, including possible control characters, and is encoded in one of various Character encoding, character encoding schemes. Some file formats, such as HTML, sca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
System Call
In computing, a system call (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. For embedded systems, system calls typically do not change the privilege mode of the CPU. 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 e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
/dev/null
In some operating systems, the null device is a device file that discards all data written to it but reports that the write operation succeeded. This device is called /dev/null on Unix and Unix-like systems, NUL: (see TOPS-20) or NUL on CP/M and DOS (internally \DEV\NUL), nul on OS/2 and newer Windows systems (internally \Device\Null on Windows NT), NIL: on Amiga operating systems, and NL: on OpenVMS. In Windows Powershell, the equivalent is $null. It provides no data to any process that reads from it, yielding EOF immediately. In IBM operating systems DOS/360 and successors and also in OS/360 and successors such files would be assigned in JCL to DD DUMMY. In programmer jargon, especially Unix jargon, it may also be called the bit bucket or black hole. History is described as an empty regular file in Version 4 Unix. The Version 5 Unix manual describes a device with modern semantics. Usage The null device is typically used for disposing of unwanted output streams of a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Duplex (telecommunications)
A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for simultaneous communication in both directions between two connected parties or to provide a reverse path for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX). In a full-duplex system, both parties can communicate with each other simultaneously. An example of a full-duplex device is plain old telephone service; the parties at both ends of a call can speak and be heard by the other party simultaneously. The earphone reproduces the speech of the remote party as the microphone transmits the speech of the local party. There is a two-way communication channel between them, or more strictly speaking, there are two communication channel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inter-process Communication
In computer science, interprocess communication (IPC) is the sharing of data between running Process (computing), processes in a computer system. Mechanisms for IPC may be provided by an operating system. Applications which use IPC are often categorized as client–server model, clients and servers, where the client requests data and the server responds to client requests. Many applications are both clients and servers, as commonly seen in distributed computing. IPC is very important to the design process for microkernels and nanokernels, which reduce the number of functionalities provided by the kernel. Those functionalities are then obtained by communicating with servers via IPC, leading to a large increase in communication when compared to a regular monolithic kernel. IPC interfaces generally encompass variable analytic framework structures. These processes ensure compatibility between the multi-vector protocols upon which IPC models rely. An IPC mechanism is either Synchroni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gnulib
Gnulib, also called the GNU portability library, is a collection of software subroutines which are designed to be usable on many operating systems. The goal of the project is to make it easy for free software authors to make their software run on many operating systems. Since source is designed to be copied from gnulib, it is not a library per-se, as much as a collection of portable idioms to be used in other projects. Making a software package work on a system other than the original system it worked on is usually called "porting" the software to the new system, and a library is a collection of subroutines which can be added to new programs. Thus, Gnulib is the GNU project's portability library. It is primarily written for use by the GNU Project, but can be used by any free software project. See also * GLib * libiberty * Boost (C++ libraries) Boost, boosted or boosting may refer to: Science, technology and mathematics * Boost, positive manifold pressure in Turbocharger, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GNU Core Utilities
The GNU Core Utilities or coreutils is a collection of GNU software that implements many standard, Unix-based shell commands. The utilities generally provide POSIX compliant interface when the environment variable is set, but otherwise offers a superset to the standard interface. For example, the utilities support long options and options after parameters. This environment variable enables a different functionality in BSD. Similar collections are available in the FOSS ecosystem, with a slightly different scope and focus (less functionality), or license. For example, BusyBox which is licensed under GPL-2.0-only, and Toybox which is licensed under 0BSD. Commands The commands implemented by coreutils are listed below. Throughout this article and customary for Unix-based systems, the term ''file'' refers to all file system items including regular files and special files such as directories. File utilities * chcon Changes file security context ( SELinux) * chgrp Chan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C (programming Language)
C (''pronounced'' '' – like the letter c'') is a general-purpose programming language. It was created in the 1970s by Dennis Ritchie and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of the targeted Central processing unit, CPUs. It has found lasting use in operating systems code (especially in Kernel (operating system), kernels), device drivers, and protocol stacks, but its use in application software has been decreasing. C is commonly used on computer architectures that range from the largest supercomputers to the smallest microcontrollers and embedded systems. A successor to the programming language B (programming language), B, C was originally developed at Bell Labs by Ritchie between 1972 and 1973 to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating system. During the 1980s, C gradually gained popularity. It has become one of the most widely used programming langu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ar (Unix)
ar, short for archiver, is a shell command for maintaining multiple files as a single archive file. Originally developed for Unix, it is widely available on Unix-based systems, and similar commands are available on other platforms. Today, ar is generally used only to create and update static library files that the link editor or linker uses and for generating .deb packages for the Debian family; it can be used to create archives for any purpose, but has been largely replaced by tar for purposes other than static libraries. An implementation of ar is included as one of the GNU Binutils. In the Linux Standard Base (LSB), ar has been deprecated and is expected to disappear in a future release of that standard. The rationale provided was that "the LSB does not include software development utilities nor does it specify .o and .a file formats." File format details The ar format has never been standardized; modern archives are based on a common format with two main variants, B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tar (computing)
In computing, tar is a shell command for combining multiple computer files into a single archive file. It was originally developed for magnetic tape storage reading and writing data for a sequential I/O device with no file system, and the name is short for the format description "tape archive". When stored in a file system, a file that tar reads and writes is often called a ''tarball''. A tarball contains metadata for the contained files including the name, ownership, timestamps, permissions and directory organization. As a file containing other files with associated metadata, a tarball is useful for software distribution and backup. POSIX abandoned ''tar'' in favor of '' pax'', yet ''tar'' continues to have widespread use. History The command was introduced to Unix in January 1979, replacing the tp program (which in turn replaced "tap"). The file structure was standardized in POSIX.1-1988 and later POSIX.1-2001, and became a format supported by most modern file ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Octal
Octal (base 8) is a numeral system with eight as the base. In the decimal system, each place is a power of ten. For example: : \mathbf_ = \mathbf \times 10^1 + \mathbf \times 10^0 In the octal system, each place is a power of eight. For example: : \mathbf_8 = \mathbf \times 8^2 + \mathbf \times 8^1 + \mathbf \times 8^0 By performing the calculation above in the familiar decimal system, we see why 112 in octal is equal to 64+8+2=74 in decimal. Octal numerals can be easily converted from binary representations (similar to a quaternary numeral system) by grouping consecutive binary digits into groups of three (starting from the right, for integers). For example, the binary representation for decimal 74 is 1001010. Two zeroes can be added at the left: , corresponding to the octal digits , yielding the octal representation 112. Usage In China The eight bagua or trigrams of the I Ching correspond to octal digits: * 0 = ☷, 1 = ☳, 2 = ☵, 3 = ☱, * 4 = ☶, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
