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FORK(2)			  FreeBSD System Calls Manual		       FORK(2)

NAME
     fork -- create a new process

LIBRARY
     Standard C	Library	(libc, -lc)

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

     pid_t
     fork(void);

DESCRIPTION
     The fork()	system call 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(2)
	       or write(2) 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 process' resource utilizations	are set	to 0; see
	       setrlimit(2).

	   +o   All interval timers are cleared;	see setitimer(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 indi-
     cate the error.

ERRORS
     The fork()	system call will fail and no child process will	be created if:

     [EAGAIN]		The system-imposed limit on the	total number of	pro-
			cesses under execution would be	exceeded.  The limit
			is given by the	sysctl(3) MIB variable KERN_MAXPROC.
			(The limit is actually ten less	than this except for
			the super user).

     [EAGAIN]		The user is not	the super user,	and the	system-imposed
			limit on the total number of processes under execution
			by a single user would be exceeded.  The limit is
			given by the sysctl(3) MIB variable
			KERN_MAXPROCPERUID.

     [EAGAIN]		The user is not	the super user,	and the	soft resource
			limit corresponding to the resource argument
			RLIMIT_NPROC would be exceeded (see getrlimit(2)).

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

SEE ALSO
     execve(2),	rfork(2), setitimer(2),	setrlimit(2), vfork(2),	wait(2)

HISTORY
     The fork()	function appeared in Version 6 AT&T UNIX.

FreeBSD	10.1			 June 4, 1993			  FreeBSD 10.1

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | HISTORY

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