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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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pathname
A path (or filepath, file path, pathname, or similar) is a text string that uniquely specifies an item in a hierarchical file system. Generally, a path is composed of directory names, special directory specifiers and optionally a filename, separated by delimiting text. The delimiter varies by operating system and in theory can be anything, but popular, modern systems use slash , backslash , or colon . A path can be either relative or absolute. A relative path includes information that is relative to a particular directory whereas an absolute path indicates a location relative to the system root directory, and therefore, does not depends on context like a relative path does. Often, a relative path is relative to the working directory. For example, in command , is a relative path to the file with that name in the working directory. Paths are used extensively in computer science to represent the directory/file relationships common in modern operating systems and are essential i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C POSIX Library
The C POSIX library is a specification of a C standard library for POSIX systems. It was developed at the same time as the ANSI C standard. Some effort was made to make POSIX compatible with standard C; POSIX includes additional functions to those introduced in standard C. On the other hand, the 5 headers that were added to the C standard library with C11, were not likewise included in subsequent revisions of POSIX. It may be included in any C++ project, however the C++ standard library may have its own implementation of certain features, such as rather than , rather than , or rather than . C POSIX library header files See also * POSIX * C standard library * C++ standard library The C standard library, sometimes referred to as libc, is the standard library for the C programming language, as specified in the ISO C standard.ISO/ IEC (2018). '' ISO/IEC 9899:2018(E): Programming Languages - C ยง7'' Starting from the origina ... References Official List of headers in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File Descriptor
In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier (handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically have non-negative integer values, with negative values being reserved to indicate "no value" or error conditions. File descriptors are a part of the POSIX API. Each Unix process (except perhaps 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 other resource) has been opened: for reading, writing, appending, and possibly other modes. It also indexes into a third table called the inode table that describes the ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Umask
umask is a shell command that reports or sets the mask value that limits the file permissions for newly created files in many Unix and Unix-like file systems. A system call with the same name, , provides access to the mask value stored in the operating system (OS), and the command provides shell user access to the system call. Additionally, the mask value, formally ''file mode creation mask'', is often referred to as the ''umask''. When a new file is created, its access permissions are restricted by the stored umask mask value. The file's permission bits that each grant access are cleared by corresponding bits of the mask that are set. Set bits of the mask disallow the permission and clear bits of the mask allow the permission. The otherwise default value of a file's permissions is defined elsewhere. The mask just prevents corresponding bits of the default. The mask acts as a last-stage filter that strips away permissions as a file is created; each bit that is set strips away ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File Permissions
Typically, a file system maintains permission settings for each stored item commonly files and directories that either grant or deny the ability to manipulate file system items. Often the settings allow controlling access based on function such as read, change, navigate, and execute and to different users and groups of users. One well-established technology was developed for Unix and later codified by POSIX. Another common technology is an access-control list (ACL) with multiple variants implemented in file systems and one codified by POSIX. Since POSIX defines both the older Unix-based technology as well as ACLs, the former is called ''traditional POSIX permissions'' for clarity even though it is not a well-known term. A permission-driven user interface tailors the functionality available to the user based on file system item permissions. For example, the interface might hide menu options that are not allowed based on the permissions stored for an item. Examples File sy ... [...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) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically have non-negative integer values, with negative values being reserved to indicate "no value" or error conditions. File descriptors are a part of the POSIX API. Each Unix process (except perhaps 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 other resource) has been opened: for reading, writing, appending, and possibly other modes. It also indexes into a third table called the inode table that describes the actual ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mask (computing)
In computer science, a mask or bitmask is data that is used for bitwise operations, particularly in a bit field. Using a mask, multiple bits in a byte, nibble, Word (computer architecture), word, etc. can be set either on or off, or inverted from on to off (or vice versa) in a single bitwise operation. An additional use of masking involves Predication (computer architecture), predication in vector processing, where the bitmask is used to select which element operations in the vector are to be executed (mask bit is enabled) and which are not (mask bit is clear). Common bitmask functions Masking bits to 1 To turn certain bits on, the Logical disjunction, bitwise OR operation can be used, following Logical disjunction#Bitwise operation, the principle that for an individual bit Y, Y OR 1 = 1 and Y OR 0 = Y. Therefore, to make sure a bit is on, OR can be used with a 1. To leave a bit unchanged, OR is used with a 0. Example: Masking ''on'' the higher nibble (bits 4, 5, 6, 7) while l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File Path
A path (or filepath, file path, pathname, or similar) is a text string that uniquely specifies an item in a hierarchical file system. Generally, a path is composed of directory names, special directory specifiers and optionally a filename, separated by delimiting text. The delimiter varies by operating system and in theory can be anything, but popular, modern systems use slash , backslash , or colon . A path can be either relative or absolute. A relative path includes information that is relative to a particular directory whereas an absolute path indicates a location relative to the system root directory, and therefore, does not depends on context like a relative path does. Often, a relative path is relative to the working directory. For example, in command , is a relative path to the file with that name in the working directory. Paths are used extensively in computer science to represent the directory/file relationships common in modern operating systems and are essential i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
โ1
In mathematics, โ1 (negative one or minus one) is the additive inverse of 1, that is, the number that when added to 1 gives the additive identity element, 0. It is the negative integer greater than negative two (โ2) and less than 0. In mathematics Algebraic properties Multiplying a number by โ1 is equivalent to changing the sign of the number โ that is, for any we have . This can be proved using the distributive law and the axiom that 1 is the multiplicative identity: :. Here we have used the fact that any number times 0 equals 0, which follows by cancellation from the equation :. In other words, :, so is the additive inverse of , i.e. , as was to be shown. The square of โ1 (that is โ1 multiplied by โ1) equals 1. As a consequence, a product of two negative numbers is positive. For an algebraic proof of this result, start with the equation :. The first equality follows from the above result, and the second follows from the definition of โ1 as addi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C (programming Language)
C (''pronounced'' '' โ 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] |
POSIX
The Portable Operating System Interface (POSIX; ) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines application programming interfaces (APIs), along with command line shells and utility interfaces, for software compatibility (portability) with variants of Unix and other operating systems. POSIX is also a trademark of the IEEE. POSIX is intended to be used by both application and system developers. As of POSIX 2024, the standard is aligned with the C17 language standard. Name Originally, the name "POSIX" referred to IEEE Std 1003.1-1988, released in 1988. The family of POSIX standards is formally designated as IEEE 1003 and the ISO/IEC standard number is ISO/ IEC 9945. The standards emerged from a project that began in 1984 building on work from related activity in the ''/usr/group'' association. Richard Stallman suggested the name ''POSIX'' to the IEEE instead of the former ''IEEE-IX''. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
