Parent process
Encyclopedia
In computing, a parent process is a process that has created one or more child process
es.
Unix
, 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 init
, is the ancestor of every other process in the system.
system call
, causing a fatal execution error
, or receiving a terminating signal
, an exit status
is returned to the operating system. The parent process is informed of its child's termination through a SIGCHLD
signal. A parent will typically retrieve its child's exit status by calling the wait
system call
. However, if a parent does not do so, the child process becomes a zombie process
.
A process that remains running even though its parent process has finished is an orphan process
. In a Unix-like
operating system any orphaned processes will be automatically adopted by the special init
system process.
, 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 signal on child's termination, whereas real parent is the thread that actually created this child process in a multithreaded environment. For a normal process, both these two values are same, but for a POSIX thread which acts as a process, these two values may be different.
Child process
A child process in computing is a process created by another process .A child process inherits most of its attributes, such as open files, from its parent. In UNIX, a child process is in fact created as a copy of the parent...
es.
Unix
In the operating systemOperating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
, every process except (the swapper) is created when another process executes the fork
Fork (operating system)
In computing, when a process forks, it creates a copy of itself. More generally, a fork in a multithreading environment means that a thread of execution is duplicated, creating a child thread from the parent thread....
system call
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
. 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
Scheduling (computing)
In computer science, a scheduling is the method by which threads, processes or data flows are given access to system resources . This is usually done to load balance a system effectively or achieve a target quality of service...
(sometimes also known as the "idle task"). , known as init
Init
init is a program for Unix-based computer operating systems that spawns all other processes. It runs as a daemon and typically has PID 1. The boot loader starts the kernel and the kernel starts init...
, is the ancestor of every other process in the system.
Zombies and orphans
When a child process terminates execution, either by calling the exitExit (operating system)
On many computer operating systems, a computer process terminates its execution by making an exit system call. More generally, an exit in a multithreading environment means that a thread of execution has stopped running. The operating system reclaims resources that were used by the process...
system call
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
, causing a fatal execution error
Fatal error
In computing, a fatal error or fatal exception error is an error that causes a program to abort and may therefore return the user to the operating system. When this happens, data that the program was processing may be lost. A fatal error is usually distinguished from a fatal system error...
, or receiving a terminating signal
Signal (computing)
A signal is a limited form of inter-process communication used in Unix, Unix-like, and other POSIX-compliant operating systems. Essentially it is an asynchronous notification sent to a process in order to notify it of an event that occurred. When a signal is sent to a process, the operating system...
, an exit status
Exit status
The exit status or return code of a process in computer programming is a small number passed from a child process to a parent process when it has finished executing a specific procedure or delegated task...
is returned to the operating system. The parent process is informed of its child's termination through a SIGCHLD
SIGCHLD
On POSIX-compliant platforms, SIGCHLD is the signal sent to a process when a child process terminates. The symbolic constant for SIGCHLD is defined in the header file signal.h. Symbolic signal names are used because signal numbers can vary across platforms....
signal. A parent will typically retrieve its child's exit status by calling the wait
Wait (operating system)
In modern computer operating systems, a process may wait on another process to complete its execution. In most systems, a parent process can create an independently executing child process. The parent process may then issue a wait system call, which suspends the execution of the parent process...
system call
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
. However, if a parent does not do so, the child process becomes a zombie process
Zombie process
On Unix and Unix-like computer operating systems, a zombie process or defunct process is a process that has completed execution but still has an entry in the process table. This entry is still needed to allow the process that started the process to read its exit status. The term zombie process...
.
A process that remains running even though its parent process has finished is an orphan process
Orphan process
An orphan process is a computer process whose parent process has finished or terminated, though itself remains running.In a Unix-like operating system any orphaned process will be immediately adopted by the special init system process. This operation is called re-parenting and occurs automatically...
. In a Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating system any orphaned processes will be automatically adopted by the special init
Init
init is a program for Unix-based computer operating systems that spawns all other processes. It runs as a daemon and typically has PID 1. The boot loader starts the kernel and the kernel starts init...
system process.
Linux kernel
In the Linux kernelLinux kernel
The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
, in which there is a very slim difference between processes and POSIX threads
POSIX Threads
POSIX Threads, usually referred to as Pthreads, is a POSIX standard for threads. The standard, POSIX.1c, Threads extensions , defines an API for creating and manipulating threads....
, there are two kinds of parent processes, namely real parent and parent. Parent is the process that receives the SIGCHLD signal on child's termination, whereas real parent is the thread that actually created this child process in a multithreaded environment. For a normal process, both these two values are same, but for a POSIX thread which acts as a process, these two values may be different.