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.TH FORK 2

.SH NAME

fork, rfork \- manipulate process resources

.SH SYNOPSIS

.B #include <u.h>

.br

.B #include <libc.h>

.PP

.nf

.B

int fork(void)

.PP

.B

int rfork(int flags)

.fi

.SH DESCRIPTION

Forking is the only way new processes are created.

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.

The resources include

the file name space,

the open file descriptor table (which, when shared, permits processes

to open and close files for other processes),

the set of environment variables

(see

.IR env (3)),

the note group

(the set of processes that receive notes written to a member's

.B notepg

file;

see

.IR proc (3)),

the set of rendezvous tags

(see

.IR rendezvous (2)); 

and open files.

.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 (2))

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 written to any of their

.B notepg

files (see

.IR proc (3)).

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.

.TP

.B RFFDG

If set, the invoker's file descriptor table (see

.IR intro (2))

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 (2)

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

.I Fork

is just a call of

.BR rfork(RFFDG|RFREND|RFPROC) .

.SH SOURCE

.B /sys/src/libc/9syscall

.br

.B /sys/src/libc/9sys/fork.c

.SH SEE ALSO

.IR intro (2),

.IR proc (3),

.SH DIAGNOSTICS

These functions set

.IR errstr .