1SETPGID(2)                 Linux Programmer's Manual                SETPGID(2)
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NAME

6       setpgid, getpgid, setpgrp, getpgrp - set/get process group
7

SYNOPSIS

9       #include <sys/types.h>
10       #include <unistd.h>
11
12       int setpgid(pid_t pid, pid_t pgid);
13       pid_t getpgid(pid_t pid);
14
15       pid_t getpgrp(void);                 /* POSIX.1 version */
16       pid_t getpgrp(pid_t pid);            /* BSD version */
17
18       int setpgrp(void);                   /* System V version */
19       int setpgrp(pid_t pid, pid_t pgid);  /* BSD version */
20
21   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
22
23       getpgid():
24           _XOPEN_SOURCE >= 500
25               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
26
27       setpgrp() (POSIX.1):
28           _XOPEN_SOURCE >= 500
29               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
30               || /* Glibc versions <= 2.19: */ _SVID_SOURCE
31
32       setpgrp() (BSD), getpgrp() (BSD):
33           [These are available only before glibc 2.19]
34           _BSD_SOURCE &&
35               ! (_POSIX_SOURCE || _POSIX_C_SOURCE || _XOPEN_SOURCE ||
36                   _GNU_SOURCE || _SVID_SOURCE)
37

DESCRIPTION

39       All  of  these interfaces are available on Linux, and are used for get‐
40       ting and setting the process group ID (PGID) of a  process.   The  pre‐
41       ferred,  POSIX.1-specified  ways  of doing this are: getpgrp(void), for
42       retrieving the calling process's PGID; and  setpgid(),  for  setting  a
43       process's PGID.
44
45       setpgid()  sets  the  PGID of the process specified by pid to pgid.  If
46       pid is zero, then the process ID of the calling process  is  used.   If
47       pgid is zero, then the PGID of the process specified by pid is made the
48       same as its process ID.  If setpgid() is used to move  a  process  from
49       one  process  group to another (as is done by some shells when creating
50       pipelines), both process groups must be part of the same  session  (see
51       setsid(2) and credentials(7)).  In this case, the pgid specifies an ex‐
52       isting process group to be joined and the session ID of that group must
53       match the session ID of the joining process.
54
55       The POSIX.1 version of getpgrp(), which takes no arguments, returns the
56       PGID of the calling process.
57
58       getpgid() returns the PGID of the process specified by pid.  If pid  is
59       zero,  the  process ID of the calling process is used.  (Retrieving the
60       PGID of a process other than the caller is rarely  necessary,  and  the
61       POSIX.1 getpgrp() is preferred for that task.)
62
63       The  System V-style  setpgrp(), which takes no arguments, is equivalent
64       to setpgid(0, 0).
65
66       The BSD-specific setpgrp() call, which takes arguments pid and pgid, is
67       a wrapper function that calls
68
69           setpgid(pid, pgid)
70
71       Since  glibc 2.19, the BSD-specific setpgrp() function is no longer ex‐
72       posed by <unistd.h>; calls should be replaced with the  setpgid()  call
73       shown above.
74
75       The  BSD-specific getpgrp() call, which takes a single pid argument, is
76       a wrapper function that calls
77
78           getpgid(pid)
79
80       Since glibc 2.19, the BSD-specific getpgrp() function is no longer  ex‐
81       posed by <unistd.h>; calls should be replaced with calls to the POSIX.1
82       getpgrp() which takes no arguments (if the  intent  is  to  obtain  the
83       caller's PGID), or with the getpgid() call shown above.
84

RETURN VALUE

86       On  success,  setpgid() and setpgrp() return zero.  On error, -1 is re‐
87       turned, and errno is set appropriately.
88
89       The POSIX.1 getpgrp() always returns the PGID of the caller.
90
91       getpgid(), and the BSD-specific getpgrp() return  a  process  group  on
92       success.  On error, -1 is returned, and errno is set appropriately.
93

ERRORS

95       EACCES An attempt was made to change the process group ID of one of the
96              children of the calling process and the child had  already  per‐
97              formed an execve(2) (setpgid(), setpgrp()).
98
99       EINVAL pgid is less than 0 (setpgid(), setpgrp()).
100
101       EPERM  An  attempt was made to move a process into a process group in a
102              different session, or to change the process group ID of  one  of
103              the  children of the calling process and the child was in a dif‐
104              ferent session, or to change the process group ID of  a  session
105              leader (setpgid(), setpgrp()).
106
107       ESRCH  For  getpgid():  pid does not match any process.  For setpgid():
108              pid is not the calling process and not a child  of  the  calling
109              process.
110

CONFORMING TO

112       setpgid()  and  the  version  of getpgrp() with no arguments conform to
113       POSIX.1-2001.
114
115       POSIX.1-2001 also specifies getpgid() and the version of setpgrp() that
116       takes  no  arguments.  (POSIX.1-2008 marks this setpgrp() specification
117       as obsolete.)
118
119       The version of getpgrp() with one argument and the version of setpgrp()
120       that  takes  two arguments derive from 4.2BSD, and are not specified by
121       POSIX.1.
122

NOTES

124       A child created via fork(2) inherits its  parent's  process  group  ID.
125       The PGID is preserved across an execve(2).
126
127       Each  process group is a member of a session and each process is a mem‐
128       ber of the session of which its process group is a member.   (See  cre‐
129       dentials(7).)
130
131       A  session can have a controlling terminal.  At any time, one (and only
132       one) of the process groups in the session can be the foreground process
133       group  for  the terminal; the remaining process groups are in the back‐
134       ground.  If a signal is generated from the terminal (e.g.,  typing  the
135       interrupt  key  to  generate  SIGINT), that signal is sent to the fore‐
136       ground process group.  (See termios(3) for a description of the charac‐
137       ters  that  generate  signals.)   Only the foreground process group may
138       read(2) from the terminal; if  a  background  process  group  tries  to
139       read(2)  from  the  terminal,  then the group is sent a SIGTTIN signal,
140       which suspends it.  The tcgetpgrp(3)  and  tcsetpgrp(3)  functions  are
141       used  to get/set the foreground process group of the controlling termi‐
142       nal.
143
144       The setpgid() and getpgrp() calls are used by programs such as  bash(1)
145       to create process groups in order to implement shell job control.
146
147       If  the  termination  of a process causes a process group to become or‐
148       phaned, and if any member  of  the  newly  orphaned  process  group  is
149       stopped, then a SIGHUP signal followed by a SIGCONT signal will be sent
150       to each process in the  newly  orphaned  process  group.   An  orphaned
151       process  group  is  one  in which the parent of every member of process
152       group is either itself also a member of the process group or is a  mem‐
153       ber  of  a  process  group  in  a  different  session (see also creden‐
154       tials(7)).
155

SEE ALSO

157       getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3),  termios(3),  creden‐
158       tials(7)
159

COLOPHON

161       This  page  is  part of release 5.10 of the Linux man-pages project.  A
162       description of the project, information about reporting bugs,  and  the
163       latest     version     of     this    page,    can    be    found    at
164       https://www.kernel.org/doc/man-pages/.
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168Linux                             2017-09-15                        SETPGID(2)
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