1 .TH FORK 3
2 .SH NAME
3 fork, rfork \- manipulate process resources
4 .SH SYNOPSIS
5 .B #include <u.h>
6 .br
7 .B #include <libc.h>
8 .PP
9 .nf
10 .B
11 int fork(void)
12 .PP
13 .B
14 int rfork(int flags)
15 .fi
16 .SH DESCRIPTION
17 Forking is the only way new processes are created.
18 The
19 .I flags
20 argument to
21 .I rfork
22 selects which resources of the
23 invoking process (parent) are shared
24 by the new process (child) or initialized to
25 their default values.
26 The resources include
27 the file name space,
28 the open file descriptor table (which, when shared, permits processes
29 to open and close files for other processes),
30 the set of environment variables
31 (see
32 .IR env (3)),
33 the note group
34 (the set of processes that receive notes written to a member's
35 .B notepg
36 file;
37 see
38 .IR proc (3)),
39 the set of rendezvous tags
40 (see
41 .IR rendezvous (3)); 
42 and open files.
43 .I Flags
44 is the logical OR of some subset of
45 .TF RFCNAMEG
46 .TP
47 .B RFPROC
48 If set a new process is created; otherwise changes affect the
49 current process.
50 .TP
51 .B RFNOWAIT
52 If set, the child process will be dissociated from the parent. Upon
53 exit the child will leave no
54 .B Waitmsg
55 (see
56 .IR wait (3))
57 for the parent to collect.
58 .TP
59 .B RFNAMEG
60 If set, the new process inherits a copy of the parent's name space;
61 otherwise the new process shares the parent's name space.
62 Is mutually exclusive with
63 .BR RFCNAMEG .
64 .TP
65 .B RFCNAMEG
66 If set, the new process starts with a clean name space. A new
67 name space must be built from a mount of an open file descriptor.
68 Is mutually exclusive with
69 .BR RFNAMEG .
70 .TP
71 .B RFNOMNT
72 If set, subsequent mounts into the new name space and dereferencing
73 of pathnames starting with
74 .B #
75 are disallowed.
76 .TP
77 .B RFENVG
78 If set, the environment variables are copied;
79 otherwise the two processes share environment variables.
80 Is mutually exclusive with
81 .BR RFCENVG .
82 .TP
83 .B RFCENVG
84 If set, the new process starts with an empty environment.
85 Is mutually exclusive with
86 .BR RFENVG .
87 .TP
88 .B RFNOTEG
89 Each process is a member of a group of processes that all
90 receive notes when a note is written to any of their
91 .B notepg
92 files (see
93 .IR proc (3)).
94 The group of a new process is by default the same as its parent, but if
95 .B RFNOTEG
96 is set (regardless of
97 .BR RFPROC ),
98 the process becomes the first in a new group, isolated from
99 previous processes.
100 .TP
101 .B RFFDG
102 If set, the invoker's file descriptor table (see
103 .IR intro (3))
104 is copied; otherwise the two processes share a
105 single table.
106 .TP
107 .B RFCFDG
108 If set, the new process starts with a clean file descriptor table.
109 Is mutually exclusive with
110 .BR RFFDG .
111 .TP
112 .B RFREND
113 If set, the process will be unable to
114 .IR rendezvous (3)
115 with any of its ancestors; its children will, however, be able to
116 .B rendezvous
117 with it.  In effect,
118 .B RFREND
119 makes the process the first in a group of processes that share a space for
120 .B rendezvous
121 tags.
122 .TP
123 .B RFMEM
124 If set, the child and the parent will share
125 .B data
126 and
127 .B bss
128 segments.
129 Otherwise, the child inherits a copy of those segments.
130 Other segment types, in particular stack segments, will be unaffected.
131 May be set only with
132 .BR RFPROC .
133 .PD
134 .PP
135 File descriptors in a shared file descriptor table are kept
136 open until either they are explicitly closed
137 or all processes sharing the table exit.
138 .PP
139 If
140 .B RFPROC
141 is set, the
142 value returned in the parent process
143 is the process id
144 of the child process; the value returned in the child is zero.
145 Without
146 .BR RFPROC ,
147 the return value is zero.
148 Process ids range from 1 to the maximum integer
149 .RB ( int )
150 value.
151 .I Rfork
152 will sleep, if necessary, until required process resources are available.
153 .PP
154 .I Fork
155 is just a call of
156 .BR rfork(RFFDG|RFREND|RFPROC) .
157 .SH SOURCE
158 .B /sys/src/libc/9syscall
159 .br
160 .B /sys/src/libc/9sys/fork.c
161 .SH SEE ALSO
162 .IR intro (3),
163 .IR proc (3),
164 .SH DIAGNOSTICS
165 These functions set
166 .IR errstr .