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

NAME
     fork — create a new process

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

	   ·   The child process has a unique process ID.

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

	   ·   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 cre‐
	       ated processes as well as to set up pipes.

	   ·   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 indi‐
     cate the error.

ERRORS
     Fork() 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.  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.

SEE ALSO
     execve(2), wait(2)

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

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