Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
RFORK(2)		    BSD	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 in-
     voking process (parent) are shared	by the new process (child) or initial-
     ized to their default values.  The	resources include the open file	de-
     scriptor table (which, when shared, permits processes to open and close
     files for other processes), and open files.  The flags argument is	the
     logical OR	of some	subset of:

     RFPROC	  If set a new process is created; otherwise changes affect
		  the current process.

     RFNOWAIT	  If set, the child process will be dissociated	from the par-
		  ent.	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 descriptor
		  table.  Is mutually exclusive	with RFFDG.

     RFTHREAD	  If set, the new process shares file descriptor to process
		  leaders table	with its parent.  Only applies when neither
		  RFFDG	nor RFCFDG are set.

     RFMEM	  If set, the kernel will force	sharing	of the entire address
		  space, typically by sharing the hardware page	table di-
		  rectly.  The child will thus inherit and share all the seg-
		  ments	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 generally	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 pro-
		  vided	stack.	See rfork_thread(3) for	information.  Note
		  that a lot of	code will not run correctly in such an envi-

     RFSIGSHARE	  If set, the kernel will force	sharing	the sigacts structure
		  between the child and	the parent.

     RFTSIGZMB	  If set, the kernel will deliver a specified signal to	the
		  parent upon the child	exit, instead of default SIGCHLD.  The
		  signal number	signum is specified by oring the
		  RFTSIGFLAGS(signum) expression into flags.  Specifying sig-
		  nal number 0 disables	signal delivery	upon the child exit.

     RFLINUXTHPN  If set, the kernel will deliver SIGUSR1 instead of SIGCHLD
		  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.  The rfork() system call will	sleep, if nec-
     essary, until required process resources are available.

     The fork()	system call can	be implemented as a call to rfork(RFFDG	|
     RFPROC) but is not	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.

     The rfork() system	call will fail and no child process will be created

     [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

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

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

     [EINVAL]		Any flags not listed above were	specified.

     [EINVAL]		An invalid signal number was specified.

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

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

     The rfork() function first	appeared in Plan9.

BSD				 July 12, 2011				   BSD


Want to link to this manual page? Use this URL:

home | help