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RFORK(2)                  OpenBSD Programmer's Manual                 RFORK(2)

NAME
     rfork - control new processes

SYNOPSIS
     #include <sys/param.h>
     #include <unistd.h>

     int
     rfork(int flags);

DESCRIPTION
     The fork functions (fork(2), vfork(2) and rfork()) create new processes.
     The new process (child process) is an exact copy of the calling process
     (parent process), except as outlined in the fork(2) manual page.  rfork()
     can be used to manipulate the resources of the parent process and the
     child process.  Operations currently supported include whether to copy or
     share the file descriptor table between the two processes, whether to
     share the address space, and whether the parent should wait(2) for the
     child process to _exit(2).  rfork() takes a single argument, flags, which
     controls which of these resources should be manipulated.  They are de-
     fined in the header file <sys/param.h> and are the logical OR of one or
     more of the following:

     RFNAMEG   New Plan 9 `name space'.  This is a Plan 9 specific flag, and
               not implemented.

     RFENVG    Copy Plan 9 `env space'.  This is a Plan 9 specific flag, and
               not implemented.

     RFFDG     Copy the parent's file descriptor table.  If this flag is un-
               set, the parent and child will share the parent's file descrip-
               tor table.  May not be used in conjunction with RFCFDG.

     RFNOTEG   Create new Plan 9 `note group'.  This is a Plan 9 specific
               flag, and not implemented.

     RFPROC    Create a new process.  The current implementation requires this
               flag to always be set.

     RFMEM     The kernel forces sharing of the entire address space.  The
               child will then inherit all the shared segments the parent pro-
               cess owns.  Subsequent forks by the parent will then propagate
               the shared data and bss between children.  The stack segment is
               always split.

     RFNOWAIT  Parent need not wait(2) on child.

     RFCNAMEG  Zero Plan 9 `name space'.  This is a Plan 9 specific flag, and
               not implemented.

     RFCENVG   Zero Plan 9 `env space'.  This is a Plan 9 specific flag, and
               not implemented.

     RFCFDG    Zero the child's file descriptor table (ie. start with a blank
               file descriptor table).  May not be used in conjunction with
               RFFDG.

RETURN VALUES
     The parent process returns the process ID (PID) of the child process.
     The child process returns 0.  The range of the process ID is defined in
     <sys/proc.h> and is currently between 1 and 32766, inclusive.

     fork() can be implemented as a call to rfork() 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:

     [ENOMEM]      Cannot allocate memory.  The new process image required
                   more memory than was allowed by the hardware or by system-
                   imposed memory management constraints.  A lack of swap
                   space is normally temporary; however, a lack of core is
                   not.  Soft limits may be increased to their corresponding
                   hard limits.

     [EINVAL]      Invalid argument.  Some invalid argument was supplied.

     [EAGAIN]      Resource temporarily unavailable.  The system-imposed limit
                   on the total number of processes under execution would be
                   exceeded.  This limit is configuration-dependent.

     [EAGAIN]      Resource temporarily unavailable.  The system-imposed limit
                   MAXUPRC on the total number of processes under execution by
                   a single user would be exceeded.  MAXUPRC is currently de-
                   fined in <sys/param.h> as CHILD_MAX, which is currently de-
                   fined as 80 in <sys/limits.h>.

SEE ALSO
     _exit(2), execve(2), fork(2), intro(2), vfork(2)

HISTORY
     The rfork() function first appeared in Plan 9.

OpenBSD 3.4                      June 17, 2003                               2

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | HISTORY

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