RFORK(2)

NAME
rfork - manipulate process resources

SYNOPSIS
#include <sys/param.h>
#include <unistd.h>
int
rfork(int flags);

DESCRIPTION
Forking, vforking or rforking is the only way new processes are created. The flags argument to rfork() selects which resources of the invoking process (parent) are shared by the new process (child) or initialized 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). This is not currently implemented.
RFNAMEG, RFCNAMEG, RFENVG, RFCENVG, RFNOTEG
    These are Plan 9 specific flags, and not implimented.
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.
RFMEM
    If set, the kernel will force sharing of the entire address space. The child will then inherit all the shared segments the parent process owns. Other segment types will be unaffected. Subsequent forks by the parent will then propagate the shared data and bss between children. The stack segment is always split. May be set only with RFPROC.

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

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. Without RFPROC, the return value is zero. Process ids 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.

ERRORS
Rfork() 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.

SEE ALSO
intro(2), fork(2), vfork(2), minherit(2)

HISTORY
The rfork() function first appeared in Plan9.