A child process in computing is a process created by another process (the parent process).
A child process inherits most of its attributes, such as file descriptors, from its parent. In Unix, a child process is typically created as a copy of the parent, using the fork system call. The child process can then overlay itself with a different program (using exec) as required.
Each process may create many child processes but will have at most one parent process; if a process does not have a parent this usually indicates that it was created directly by the kernel. In some systems, including Unix based systems such as Linux, the very first process (called init) is started by the kernel at booting time and never terminates (see Linux startup process); other parentless processes may be launched to carry out various daemon tasks in userspace. Another way for a process to end up without a parent is if its parent dies, leaving an orphan process; but in this case it will shortly be adopted by init.
The SIGCHLD signal is sent to the parent of a child process when it exits, is interrupted, or resumes after being interrupted. By default the signal is simply ignored.
When a child process terminates before the parent has called wait, the kernel retains some information about the process, such as its exit status, to enable its parent to call wait later.. Because the child is still consuming system resources but not executing it is known as a zombie process. The wait system call is commonly invoked in the SIGCHLD handler.
POSIX.1-2001 allows a parent process to elect for the kernel to automatically reap child processes that terminate by setting the disposition of SIGCHLD to SIG_IGN (which is the default), or by setting the SA_NOCLDWAIT flag for the SIGCHLD signal; Linux 2.6 kernels adhere to this behavior, and FreeBSD supports both of these methods since version 5.0 . However, because of historical differences between System V and BSD behaviors with regard to ignoring SIGCHLD, calling wait remains the most portable paradigm for cleaning up after forked child processes.
Famous quotes containing the words child and/or process:
“A child should always say what’s true
And speak when he is spoken to,
And behave mannerly at table;
At least as far as he is able.”
—Robert Louis Stevenson (1850–1894)
“Thinking is seeing.... Every human science is based on deduction, which is a slow process of seeing by which we work up from the effect to the cause; or, in a wider sense, all poetry like every work of art proceeds from a swift vision of things.”
—Honoré De Balzac (1799–1850)