RFORK(2)                  OpenBSD Programmer's Manual                 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).
           RFNAMEG, RFCNAMEG, RFENVG, RFCENVG, RFNOTEG
                     These are Plan 9 specific flags, and not implemented.
           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 ad-
                     dress 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 ex-
     it.

     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 ids range from 1 to the
     maximum integer int value.  rfork() will sleep, if necessary, until re-
     quired process resources are available.

     fork() can be implemented as a call to rfork(2) using "RFFDG|RFPROC" but
     isn't for backwards compatibility.  If a process has file descriptor
     table sharing active, setuid or setgid programs will not execve(2) with
     extra privileges.

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 configu-
                   ration-dependent.

     [EAGAIN]      The system-imposed limit MAXUPRC (<sys/param.h>) on the to-
                   tal number of processes under execution by a single user

                   would be exceeded.

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

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

HISTORY
     The rfork() function first appeared in Plan9.

OpenBSD 2.6                    January 12, 1996                              2