|
Orphan Process
An orphan process is a computer process whose parent process has finished or terminated, though it remains running itself. Unix-like In a Unix-like operating system any orphaned process will be immediately adopted by an implementation-defined system process: the kernel sets the parent to this process. This operation is called ''re-parenting'' and occurs automatically. Even though technically the process has a system process as its parent, it is still called an orphan process since the process that originally created it no longer exists. In other systems orphaned processes are immediately terminated by the kernel. Most Unix systems have historically used ''init'' as the system process to which orphans are reparented, but in modern DragonFly BSD, FreeBSD, and Linux systems, an orphan process may be reparented to a "subreaper" process instead of ''init''. A process can be orphaned unintentionally, such as when the parent process terminates or crashes. The process group mechanism i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Process (computing)
In computing, a process is the Instance (computer science), instance of a computer program that is being executed by one or many thread (computing), threads. There are many different process models, some of which are light weight, but almost all processes (even entire virtual machines) are rooted in an operating system (OS) process which comprises the program code, assigned system resources, physical and logical access permissions, and data structures to initiate, control and coordinate execution activity. Depending on the OS, a process may be made up of multiple threads of execution that execute instructions Concurrency (computer science), concurrently. While a computer program is a passive collection of Instruction set, instructions typically stored in a file on disk, a process is the execution of those instructions after being loaded from the disk into memory. Several processes may be associated with the same program; for example, opening up several instances of the same progra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Job Control (Unix)
In Unix and Unix-like operating systems, job control refers to control of jobs by a shell, especially interactively, where a "job" is a shell's representation for a process group. Basic job control features are the suspending, resuming, or terminating of all processes in the job/process group; more advanced features can be performed by sending signals to the job. Job control is of particular interest in Unix due to its multiprocessing, and should be distinguished from job control generally, which is frequently applied to sequential execution (batch processing). Overview When using Unix or Unix-like operating systems via a terminal (or terminal emulator), a user will initially only have a single process running, their interactive shell (it may or may not be a login shell). Most tasks (directory listing, editing files, etc.) can easily be accomplished by letting the program take control of the terminal and returning control to the shell when the program exits – formally, by atta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Terminal Multiplexer
A terminal multiplexer is a software application that can be used to multiplex several separate pseudoterminal-based login sessions inside a single terminal display, terminal emulator window, PC/workstation system console, or remote login session, or to detach and reattach sessions from a terminal. It is useful for dealing with multiple programs from a command line interface, and for separating programs from the session of the Unix shell that started the program, particularly so a remote process continues running even when the user is disconnected. Features A terminal multiplexer can be thought of as a text version of graphical window managers, or as a way of putting attach virtual terminals to any login session. It is a wrapper that allows multiple text programs to run at the same time, and provides features that allow the user to use the programs within a single interface productively. ; Persistence: Similar to Virtual Network Computing, many terminal multiplexers allow the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Service Wrapper
A service wrapper is a computer program that wraps arbitrary programs thus enabling them to be installed and run as Windows Services or Unix daemons, programs that run in the background, rather than under the direct control of a user. They are often automatically started at boot time. Arbitrary programs cannot run as services or daemons, unless they fulfil specific requirements which depend on the operating system. They also have to be installed in order for the operating system to identify them as such. Various projects exist offering a Java service wrapper, as Java itself doesn't support creating system services. Some wrappers may add additional functionality to monitor the health of the application or to communicate with it. See also * Windows Service In Windows NT operating systems, a Windows service is a computer program that operates in the background. It is similar in concept to a Unix daemon. A Windows service must conform to the interface rules and protocols of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disown (Unix)
In the Unix shells ksh, bash, fish and zsh, the disown builtin command is used to remove jobs from the job table, or to mark jobs so that a SIGHUP signal is not sent to them if the parent shell receives it (e.g. if the user logs out). See also * nohup, a 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 comm ... command to ignore the HUP (hangup) signal External links Bash Reference Manual: Job Control Builtins {{Unix commands System administration ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nohup
nohup is a POSIX command which means "no hang up". Its purpose is to execute a command such that it ignores the HUP (hangup) signal and therefore does not stop when the user logs out. Output that would normally go to the terminal goes to a file called , if it has not already been redirected. Use The first of the commands below starts the program abcd in the background in such a way that the subsequent logout does not stop it. $ nohup abcd & $ exit Note that these methods prevent the process from being sent a 'stop' signal on logout, but if input/output is being received for these standard I/O files (stdin, stdout, or stderr), they will still hang the terminal. See Overcoming hanging, below. nohup is often used in combination with the nice command to run processes on a lower priority. $ nohup nice abcd & Implementations Some shells (e.g. bash) provide a shell builtin that may be used to prevent SIGHUP being sent or propagated to existing jobs, even if they were not sta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fork (system Call)
In computing, particularly in the context of the Unix operating system and Unix-like, its workalikes, fork is an operation whereby a Computer process, process creates a copy of itself. It is an interface which is required for compliance with the POSIX and Single UNIX Specification standards. It is usually implemented as a C standard library Wrapper library, wrapper to the fork, clone, or other system calls of the kernel (operating system), kernel. Fork is the primary method of process creation on Unix-like operating systems. Overview In multitasking operating systems, processes (running programs) need a way to create new processes, e.g. to run other programs. Fork and its variants are typically the only way of doing so in Unix-like systems. For a process to start the execution of a different program, it first forks to create a copy of itself. Then, the copy, called the "child process", makes any environment changes the child will need and then calls the exec (system call), exec s ... [...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] |
Login Session
In computing, a login session is the period of activity between a user logging in and logging out of a (multi-user) system. On Unix and Unix-like operating systems, a login session takes one of two main forms: * When a textual user interface is used, a login session is represented as a kernel session — a collection of process groups with the logout action managed by a session leader. * Where an X display manager is employed, a login session is considered to be the lifetime of a designated user process that the display manager invokes. On Windows NT-based systems, login sessions are maintained by the kernel and control of them is overseen by the Local Security Authority Subsystem Service (LSA). winlogon responds to the secure attention key, it requests the LSA to create login sessions on login, and terminates all of the processes belonging to a login session on logout. See also * Booting process of Windows NT * Architecture of Windows NT * Booting * Master boot recor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SIGHUP
On POSIX-compliant platforms, SIGHUP ("signal hang up") is a signal sent to a process when its controlling terminal is closed. It was originally designed to notify the process of a serial line drop. SIGHUP is a symbolic constant defined in the header file signal.h. History Access to computer systems for many years consisted of connecting a terminal to a mainframe system via a serial line and the RS-232 protocol. When a system of software interrupts, called signals, was being developed, one of those signals was designated for use on hangup. SIGHUP would be sent to programs when the serial line was dropped, often because the connected user terminated the connection by hanging up the modem. The system would detect the line was dropped via the lost Data Carrier Detect (DCD) signal. Signals have always been a convenient method of inter-process communication (IPC), but in early implementations there were no user-definable signals (such as the later additions of SIGUSR1 and SIGU ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parent Process
In computing, a parent process is a process that has created one or more child processes. Unix-like systems In Unix-like operating systems, every process except (the swapper) is created when another process executes the fork() system call. The process that invoked fork is the ''parent process'' and the newly created process is the ''child process''. Every process (except process 0) has one parent process, but can have many child processes. The operating system kernel identifies each process by its process identifier. is a special process that is created when the system boots; after forking a child process becomes the swapper process (sometimes also known as the " idle task"). , known as , is the ancestor of every other process in the system. Linux In the Linux kernel, in which there is a very slim difference between processes and POSIX threads, there are two kinds of parent processes, namely real parent and parent. Parent is the process that receives the ''SIGCHLD'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix Shell
A Unix shell is a Command-line_interface#Command-line_interpreter, command-line 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 exe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
