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32 .\" @(#)getpgrp.2 6.4 (Berkeley) 3/10/91
33 .\"
34 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
35 .\" Modified 1995-04-15 by Michael Chastain <mec@shell.portal.com>:
36 .\" Added 'getpgid'.
37 .\" Modified 1996-07-21 by Andries Brouwer <aeb@cwi.nl>
38 .\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
39 .\" Modified 1999-09-02 by Michael Haardt <michael@moria.de>
40 .\" Modified 2002-01-18 by Michael Kerrisk <mtk-manpages@gmx.net>
41 .\" Modified 2003-01-20 by Andries Brouwer <aeb@cwi.nl>
42 .\"
43 .TH SETPGID 2 2003-01-20 "Linux" "Linux Programmer's Manual"
44 .SH NAME
45 setpgid, getpgid, setpgrp, getpgrp \- set/get process group
46 .SH SYNOPSIS
47 .B #include <unistd.h>
48 .sp
49 .BI "int setpgid(pid_t " pid ", pid_t " pgid );
50 .br
51 .BI "pid_t getpgid(pid_t " pid );
52 .br
53 .B int setpgrp(void);
54 .br
55 .B pid_t getpgrp(void);
56 .SH DESCRIPTION
57 .BR setpgid ()
58 sets the process group ID of the process specified by
59 .I pid
60 to
61 .IR pgid .
62 If
63 .I pid
64 is zero, the process ID of the current process is used. If
65 .I pgid
66 is zero, the process ID of the process specified by
67 .I pid
68 is used. If \fBsetpgid\fP() is used to move a process from one process
69 group to another (as is done by some shells when creating pipelines),
70 both process groups must be part of the same session. In this case,
71 the \fIpgid\fP specifies an existing process group to be joined and the
72 session ID of that group must match the session ID of the joining process.
73
74 .BR getpgid ()
75 returns the process group ID of the process specified by
76 .IR pid .
77 If
78 .I pid
79 is zero, the process ID of the current process is used.
80
81 The call
82 .BR setpgrp ()
83 is equivalent to
84 .BR setpgid(0,0) .
85
86 Similarly,
87 .BR getpgrp ()
88 is equivalent to
89 .BR getpgid(0) .
90 Each process group is a member of a session and each process is a
91 member of the session of which its process group is a member.
92
93 Process groups are used for distribution of signals, and by terminals to
94 arbitrate requests for their input: Processes that have the same process
95 group as the terminal are foreground and may read, while others will
96 block with a signal if they attempt to read.
97 These calls are thus used by programs such as
98 .BR csh (1)
99 to create process groups in implementing job control. The
100 .B TIOCGPGRP
101 and
102 .B TIOCSPGRP
103 calls described in
104 .BR termios (3)
105 are used to get/set the process group of the control terminal.
106
107 If a session has a controlling terminal, CLOCAL is not set and a hangup
108 occurs, then the session leader is sent a SIGHUP. If the session leader
109 exits, the SIGHUP signal will be sent to each process in the foreground
110 process group of the controlling terminal.
111
112 If the exit of the process causes a process group to become orphaned,
113 and if any member of the newly-orphaned process group is stopped, then a
114 SIGHUP signal followed by a SIGCONT signal will be sent to each process
115 in the newly-orphaned process group.
116 .SH "RETURN VALUE"
117 On success,
118 .BR setpgid ()
119 and
120 .BR setpgrp ()
121 return zero. On error, \-1 is returned, and
122 .I errno
123 is set appropriately.
124
125 .BR getpgid ()
126 returns a process group on success.
127 On error, \-1 is returned, and
128 .I errno
129 is set appropriately.
130
131 .BR getpgrp ()
132 always returns the current process group.
133 .SH ERRORS
134 .TP
135 .B EACCES
136 An attempt was made to change the process group ID
137 of one of the children of the calling process and the child had
138 already performed an \fBexecve\fP()
139 (\fBsetpgid\fP(), \fBsetpgrp\fP()).
140 .TP
141 .B EINVAL
142 .I pgid
143 is less than 0
144 (\fBsetpgid\fP(), \fBsetpgrp\fP()).
145 .TP
146 .B EPERM
147 An attempt was made to move a process into a process group in a
148 different session, or to change the process
149 group ID of one of the children of the calling process and the
150 child was in a different session, or to change the process group ID of
151 a session leader
152 (\fBsetpgid\fP(), \fBsetpgrp\fP()).
153 .TP
154 .B ESRCH
155 For
156 .BR getpgid ():
157 .I pid
158 does not match any process.
159 For
160 .BR setpgid ():
161 .I pid
162 is not the current process and not a child of the current process.
163 .SH "CONFORMING TO"
164 The functions
165 .BR setpgid ()
166 and
167 .BR getpgrp ()
168 conform to POSIX.1-2001.
169 The function
170 .BR setpgrp ()
171 is from 4.2BSD.
172 The function
173 .BR getpgid ()
174 conforms to SVr4.
175 .SH NOTES
176 A child created via
177 .BR fork (2)
178 inherits its parent's process group ID.
179 The process group ID is preserved across an
180 .BR execve (2).
181
182 POSIX took
183 .BR setpgid ()
184 from the BSD function
185 .BR setpgrp ().
186 Also System V has a function with the same name, but it is identical to
187 .BR setsid (2).
188 .LP
189 To get the prototypes under glibc, define both _XOPEN_SOURCE and
190 _XOPEN_SOURCE_EXTENDED, or use "#define _XOPEN_SOURCE \fIn\fP"
191 for some integer \fIn\fP larger than or equal to 500.
192 .SH "SEE ALSO"
193 .BR getuid (2),
194 .BR setsid (2),
195 .BR tcgetpgrp (3),
196 .BR tcsetpgrp (3),
197 .BR termios (3),
198 .BR feature_test_macros (7)