.\"	$OpenBSD: rfork.2,v 1.19 2003/06/18 11:05:21 jmc Exp $
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.\" Copyright (c) 2003 Jason McIntyre <jmc@openbsd.org>
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.Dd June 17, 2003
.Dt RFORK 2
.Os
.Sh NAME
.Nm rfork
.Nd control new processes
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <unistd.h>
.Ft int
.Fn rfork "int flags"
.Sh DESCRIPTION
The fork functions
.Pf ( Xr fork 2 ,
.Xr vfork 2
and
.Fn rfork )
create new processes.
The new process (child process) is an exact copy of the calling process
(parent process), except as outlined in the
.Xr fork 2
manual page.
.Fn 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
.Xr wait 2
for the child process to
.Xr _exit 2 .
.Fn rfork
takes a single argument,
.Fa flags ,
which controls which of these resources should be manipulated.
They are defined in the header file
.Aq Pa sys/param.h
and are the logical OR of one or more of the following:
.Pp
.Bl -tag -width "RFNOWAIT"
.It Dv RFNAMEG
New Plan 9
.Sq name space .
This is a Plan 9 specific flag, and not implemented.
.It Dv RFENVG
Copy Plan 9
.Sq env space .
This is a Plan 9 specific flag, and not implemented.
.It Dv RFFDG
Copy the parent's file descriptor table.
If this flag is unset, the parent and child will share the parent's
file descriptor table.
May not be used in conjunction with
.Dv RFCFDG .
.It Dv RFNOTEG
Create new Plan 9
.Sq note group .
This is a Plan 9 specific flag, and not implemented.
.It Dv RFPROC
Create a new process.
The current implementation requires this flag to always be set.
.It Dv RFMEM
The kernel forces sharing of the entire address space.
The child will then inherit all the shared segments the parent process owns.
Subsequent forks by the parent will then propagate the shared
data and bss between children.
The stack segment is always split.
.It Dv RFNOWAIT
Parent need not
.Xr wait 2
on child.
.It Dv RFCNAMEG
Zero Plan 9
.Sq name space .
This is a Plan 9 specific flag, and not implemented.
.It Dv RFCENVG
Zero Plan 9
.Sq env space .
This is a Plan 9 specific flag, and not implemented.
.It Dv RFCFDG
Zero the child's file descriptor table (ie. start with a blank file
descriptor table).
May not be used in conjunction with
.Dv RFFDG .
.El
.Sh 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
.Aq Pa sys/proc.h
and is currently between 1 and 32766, inclusive.
.Pp
.Fn fork
can be implemented as a call to
.Fn 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
.Xr execve 2
with extra privileges.
.Sh ERRORS
.Fn rfork
will fail and no child process will be created if:
.Bl -tag -width Er
.It Bq Er 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.
.It Bq Er EINVAL
Invalid argument.
Some invalid argument was supplied.
.It Bq Er EAGAIN
Resource temporarily unavailable.
The system-imposed limit on the total
number of processes under execution would be exceeded.
This limit is configuration-dependent.
.It Bq Er EAGAIN
Resource temporarily unavailable.
The system-imposed limit
.Dv MAXUPRC
on the total number of processes under execution by a single user would be
exceeded.
.Dv MAXUPRC
is currently defined in
.Aq Pa sys/param.h
as
.Dv CHILD_MAX ,
which is currently defined as 80 in
.Aq Pa sys/limits.h .
.El
.Sh SEE ALSO
.Xr _exit 2 ,
.Xr execve 2 ,
.Xr fork 2 ,
.Xr intro 2 ,
.Xr vfork 2
.Sh HISTORY
The
.Fn rfork
function first appeared in Plan 9.