setpgid(2)

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

DESCRIPTION

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

85       On  success,  setpgid() and setpgrp() return zero.  On error, -1 is re‐
86       turned, and errno is set to indicate the error.
87
88       The POSIX.1 getpgrp() always returns the PGID of the caller.
89
90       getpgid(), and the BSD-specific getpgrp() return  a  process  group  on
91       success.   On  error,  -1 is returned, and errno is set to indicate the
92       error.
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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()).
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99       EINVAL pgid is less than 0 (setpgid(), setpgrp()).
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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()).
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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.
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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.
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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

COLOPHON

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168Linux                             2021-03-22                        SETPGID(2)