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+.TH RFORK 3
+.SH NAME
+rfork \- manipulate process state
+.SH SYNOPSIS
+.B #include <u.h>
+.br
+.B #include <libc.h>
+.PP
+.nf
+.B
+int rfork(int flags)
+.fi
+.SH DESCRIPTION
+.I Rfork
+is a partial implementation of the Plan 9 system call.
+It can be used to manipulate some process state and to create
+new processes a la 
+.IR fork (2).
+It cannot be used to create shared-memory processes 
+(Plan 9's
+.B RFMEM
+flag); for that functionality use
+.I proccreate
+(see 
+.IR thread (3)).
+.PP
+The
+.I flags
+argument to
+.I rfork
+selects which resources of the
+invoking process (parent) are shared
+by the new process (child) or initialized to
+their default values.
+.I Flags
+is the logical OR of some subset of
+.TF RFCNAMEG
+.TP
+.B RFPROC
+If set a new process is created; otherwise changes affect the
+current process.
+.TP
+.B RFNOWAIT
+If set, the child process will be dissociated from the parent. Upon
+exit the child will leave no
+.B Waitmsg
+(see
+.IR wait (3))
+for the parent to collect.
+.\" .TP
+.\" .B RFNAMEG
+.\" If set, the new process inherits a copy of the parent's name space;
+.\" otherwise the new process shares the parent's name space.
+.\" Is mutually exclusive with
+.\" .BR RFCNAMEG .
+.\" .TP
+.\" .B RFCNAMEG
+.\" If set, the new process starts with a clean name space. A new
+.\" name space must be built from a mount of an open file descriptor.
+.\" Is mutually exclusive with
+.\" .BR RFNAMEG .
+.\" .TP
+.\" .B RFNOMNT
+.\" If set, subsequent mounts into the new name space and dereferencing
+.\" of pathnames starting with
+.\" .B #
+.\" are disallowed.
+.\" .TP
+.\" .B RFENVG
+.\" If set, the environment variables are copied;
+.\" otherwise the two processes share environment variables.
+.\" Is mutually exclusive with
+.\" .BR RFCENVG .
+.\" .TP
+.\" .B RFCENVG
+.\" If set, the new process starts with an empty environment.
+.\" Is mutually exclusive with
+.\" .BR RFENVG .
+.TP
+.B RFNOTEG
+Each process is a member of a group of processes that all
+receive notes when a note is sent to the group
+(see
+.IR postnote (3)
+and
+.IR signal (2)).
+The group of a new process is by default the same as its parent, but if
+.B RFNOTEG
+is set (regardless of
+.BR RFPROC ),
+the process becomes the first in a new group, isolated from
+previous processes.
+In Plan 9, a process can call
+.B rfork(RFNOTEG)
+and then be sure that it will no longer receive console interrupts
+or other notes.
+Unix job-control shells put each command in its own process group
+and then relay notes to the current foreground command, making
+the idiom less useful.
+.TP
+.B RFFDG
+If set, the invoker's file descriptor table (see
+.IR intro ( ))
+is copied; otherwise the two processes share a
+single table.
+.\" .TP
+.\" .B RFCFDG
+.\" If set, the new process starts with a clean file descriptor table.
+.\" Is mutually exclusive with
+.\" .BR RFFDG .
+.\" .TP
+.\" .B RFREND
+.\" If set, the process will be unable to
+.\" .IR rendezvous (3)
+.\" with any of its ancestors; its children will, however, be able to
+.\" .B rendezvous
+.\" with it.  In effect,
+.\" .B RFREND
+.\" makes the process the first in a group of processes that share a space for
+.\" .B rendezvous
+.\" tags.
+.\" .TP
+.\" .B RFMEM
+.\" If set, the child and the parent will share
+.\" .B data
+.\" and
+.\" .B bss
+.\" segments.
+.\" Otherwise, the child inherits a copy of those segments.
+.\" Other segment types, in particular stack segments, will be unaffected.
+.\" May be set only with
+.\" .BR RFPROC .
+.PD
+.PP
+File descriptors in a shared file descriptor table are kept
+open until either they are explicitly closed
+or all processes sharing the table exit.
+.PP
+If
+.B 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
+.BR RFPROC ,
+the return value is zero.
+Process ids range from 1 to the maximum integer
+.RB ( int )
+value.
+.I Rfork
+will sleep, if necessary, until required process resources are available.
+.PP
+Calling
+.B rfork(RFFDG|RFPROC)
+is equivalent to calling
+.IR fork (2).
+.SH SOURCE
+.B /usr/local/plan9/src/lib9/rfork.c
+.SH DIAGNOSTICS
+.I Rfork
+sets
+.IR errstr .