fork(2) [osx man page]

FORK(2) 						      BSD System Calls Manual							   FORK(2)

NAME

     fork -- create a new process

SYNOPSIS

     #include <unistd.h>

     pid_t
     fork(void);

DESCRIPTION

     Fork() causes creation of a new process.  The new process (child process) is an exact copy of the calling process (parent process) except for
     the following:

	   o   The child process has a unique process ID.

	   o   The child process has a different parent process ID (i.e., the process ID of the parent process).

	   o   The child process has its own copy of the parent's descriptors.	These descriptors reference the same underlying objects, so that,
	       for instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in the
	       child process can affect a subsequent read or write by the parent.  This descriptor copying is also used by the shell to establish
	       standard input and output for newly created processes as well as to set up pipes.

	   o   The child processes resource utilizations are set to 0; see setrlimit(2).

RETURN VALUES

     Upon successful completion, fork() returns a value of 0 to the child process and returns the process ID of the child process to the parent
     process.  Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
     indicate the error.

ERRORS

     Fork() will fail and no child process will be created if:

     [EAGAIN]		The system-imposed limit on the total number of processes under execution would be exceeded.  This limit is configuration-
			dependent.

     [EAGAIN]		The system-imposed limit MAXUPRC (<sys/param.h>) on the total number of processes under execution by a single user would
			be exceeded.

     [ENOMEM]		There is insufficient swap space for the new process.

LEGACY SYNOPSIS

     #include <sys/types.h>
     #include <unistd.h>

     The include file <sys/types.h> is necessary.

SEE ALSO

     execve(2), sigaction(2), wait(2), compat(5)

HISTORY

     A fork() function call appeared in Version 6 AT&T UNIX.

CAVEATS

     There are limits to what you can do in the child process.	To be totally safe you should restrict yourself to only executing async-signal
     safe operations until such time as one of the exec functions is called.  All APIs, including global data symbols, in any framework or library
     should be assumed to be unsafe after a fork() unless explicitly documented to be safe or async-signal safe.  If you need to use these frame-
     works in the child process, you must exec.  In this situation it is reasonable to exec yourself.

4th Berkeley Distribution					   June 4, 1993 					 4th Berkeley Distribution

Check Out this Related Man Page

PTHREAD_ATFORK(3)					   BSD Library Functions Manual 					 PTHREAD_ATFORK(3)

NAME

     pthread_atfork -- register handlers to be called when process forks

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <pthread.h>

     int
     pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void));

DESCRIPTION

     The pthread_atfork() function registers the provided handler functions to be called when the fork(2) function is called.  Each of the three
     handlers is called at a different place in the fork(2) sequence.  The prepare handler is called in the parent process before the fork hap-
     pens, the parent handler is called in the parent process after the fork has happened, and the child handler is called in the child process
     after the fork has happened.  The parent and child handlers are called in the order in which they were registered, while the prepare handlers
     are called in reverse of the order in which they were registered.

     Any of the handlers given may be NULL.

     The intended use of pthread_atfork() is to provide a consistent state to a child process from a multithreaded parent process where locks may
     be acquired and released asynchronously with respect to the fork(2) call.	Each subsystem with locks that are used in a child process should
     register handlers with pthread_atfork() that acquires those locks in the prepare handler and releases them in the parent handler.

RETURN VALUES

     The pthread_atfork() function returns 0 on success and an error number on failure.

ERRORS

     The following error code may be returned:

     [ENOMEM]		Insufficient memory exists to register the fork handlers.

SEE ALSO

     fork(2)

STANDARDS

     The pthread_atfork() function conforms to IEEE Std 1003.1c-1995 (``POSIX.1'').

HISTORY

     The pthread_atfork() function first appeared in NetBSD 2.0.

CAVEATS

     After calling fork(2) from a multithreaded process, it is only safe to call async-signal-safe functions until calling one of the exec(3)
     functions.  The pthread_*() functions are not async-signal-safe, so it is not safe to use such functions in the child handler.

BUGS

     There is no way to unregister a handler registered with pthread_atfork().

BSD
								 February 12, 2003							       BSD

Linux and UNIX Man Pages

fork(2) [osx man page]

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