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RFORK(2)		  FreeBSD System Calls Manual		      RFORK(2)

     rfork -- manipulate process resources

     Standard C	Library	(libc, -lc)

     #include <unistd.h>

     rfork(int flags);

     Forking, vforking or rforking are the only	ways new processes are cre-
     ated.  The	flags argument to rfork() selects which	resources of the
     invoking process (parent) are shared by the new process (child) or	ini-
     tialized to their default values.	The resources include the open file
     descriptor	table (which, when shared, permits processes to	open and close
     files for other processes), and open files.  Flags	is the logical OR of
     some subset of:
	   RFPROC    If	set a new process is created; otherwise	changes	affect
		     the current process.  The current implementation requires
		     this flag to always be set.
	   RFNOWAIT  If	set, the child process will be dissociated from	the
		     parent.  Upon exit	the child will not leave a status for
		     the parent	to collect.  See wait(2).
	   RFFDG     If	set, the invoker's file	descriptor table (see
		     intro(2)) is copied; otherwise the	two processes share a
		     single table.
	   RFCFDG    If	set, the new process starts with a clean file descrip-
		     tor table.	 Is mutually exclusive with RFFDG.
	   RFMEM     If	set, the kernel	will force sharing of the entire
		     address space, typically by sharing the hardware page ta-
		     ble directly.  The	child will thus	inherit	and share all
		     the segments the parent process owns, whether they	are
		     normally shareable	or not.	 The stack segment is not
		     split (both the parent and	child return on	the same
		     stack) and	thus rfork() with the RFMEM flag may not gen-
		     erally be called directly from high level languages
		     including C.  May be set only with	RFPROC.	 A helper
		     function is provided to assist with this problem and will
		     cause the new process to run on the provided stack.  See
		     rfork_thread(3) for information.
		     If	set, the kernel	will force sharing the sigacts struc-
		     ture between the child and	the parent.
		     If	set, the kernel	will return SIGUSR1 instead of
		     SIGCHILD upon thread exit for the child.  This is
		     intended to mimic certain Linux clone behaviour.

     File descriptors in a shared file descriptor table	are kept open until
     either they are explicitly	closed or all processes	sharing	the table

     If	RFPROC is set, the value returned in the parent	process	is the process
     id	of the child process; the value	returned in the	child is zero.	With-
     out RFPROC, the return value is zero.  Process id's range from 1 to the
     maximum integer (int) value.  Rfork() will	sleep, if necessary, until
     required process resources	are available.

     Fork() can	be implemented as a call to rfork(RFFDG	| RFPROC) but isn't
     for backwards compatibility.

     Upon successful completion, rfork() 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.

     Rfork() 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 one 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

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

     [EINVAL]		The RFPROC flag	was not	specified.

     [EINVAL]		Both the RFFDG and the RFCFDG flags were specified.

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

     fork(2), intro(2),	minherit(2), vfork(2), rfork_thread(3)

     FreeBSD does not yet implement a native clone() library call, and the
     current pthreads implementation does not use rfork() with RFMEM.  A
     native port of the	linux threads library, /usr/ports/devel/linuxthreads,
     contains a	working	clone()	call that utilizes RFMEM.  The rfork_thread()
     library call can often be used instead of clone().

     The rfork() function call first appeared in Plan9.

FreeBSD	11.1		       January 12, 1996			  FreeBSD 11.1


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