setpgrp(2)

1setpgid(2)                    System Calls Manual                   setpgid(2)
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NAME

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

LIBRARY

9       Standard C library (libc, -lc)
10

SYNOPSIS

12       #include <unistd.h>
13
14       int setpgid(pid_t pid, pid_t pgid);
15       pid_t getpgid(pid_t pid);
16
17       pid_t getpgrp(void);                            /* POSIX.1 version */
18       [[deprecated]] pid_t getpgrp(pid_t pid);        /* BSD version */
19
20       int setpgrp(void);                              /* System V version */
21       [[deprecated]] int setpgrp(pid_t pid, pid_t pgid);  /* BSD version */
22
23   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24
25       getpgid():
26           _XOPEN_SOURCE >= 500
27               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
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29       setpgrp() (POSIX.1):
30           _XOPEN_SOURCE >= 500
31               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
32               || /* glibc <= 2.19: */ _SVID_SOURCE
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34       setpgrp() (BSD), getpgrp() (BSD):
35           [These are available only before glibc 2.19]
36           _BSD_SOURCE &&
37               ! (_POSIX_SOURCE || _POSIX_C_SOURCE || _XOPEN_SOURCE
38                   || _GNU_SOURCE || _SVID_SOURCE)
39

DESCRIPTION

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

88       On  success,  setpgid() and setpgrp() return zero.  On error, -1 is re‐
89       turned, and errno is set to indicate the error.
90
91       The POSIX.1 getpgrp() always returns the PGID of the caller.
92
93       getpgid(), and the BSD-specific getpgrp() return  a  process  group  on
94       success.   On  error,  -1 is returned, and errno is set to indicate the
95       error.
96

ERRORS

98       EACCES An attempt was made to change the process group ID of one of the
99              children  of  the calling process and the child had already per‐
100              formed an execve(2) (setpgid(), setpgrp()).
101
102       EINVAL pgid is less than 0 (setpgid(), setpgrp()).
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104       EPERM  An attempt was made to move a process into a process group in  a
105              different  session,  or to change the process group ID of one of
106              the children of the calling process and the child was in a  dif‐
107              ferent  session,  or to change the process group ID of a session
108              leader (setpgid(), setpgrp()).
109
110       EPERM  The target process group  does  not  exist.   (setpgid(),  setp‐
111              grp()).
112
113       ESRCH  For  getpgid():  pid does not match any process.  For setpgid():
114              pid is not the calling process and not a child  of  the  calling
115              process.
116

STANDARDS

118       getpgid()
119       setpgid()
120       getpgrp() (no args)
121       setpgrp() (no args)
122              POSIX.1-2008 (but see HISTORY).
123
124       setpgrp() (2 args)
125       getpgrp() (1 arg)
126              None.
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HISTORY

129       getpgid()
130       setpgid()
131       getpgrp() (no args)
132              POSIX.1-2001.
133
134       setpgrp() (no args)
135              POSIX.1-2001.  POSIX.1-2008 marks it as obsolete.
136
137       setpgrp() (2 args)
138       getpgrp() (1 arg)
139              4.2BSD.
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NOTES

142       A  child  created  via  fork(2) inherits its parent's process group ID.
143       The PGID is preserved across an execve(2).
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145       Each process group is a member of a session and each process is a  mem‐
146       ber  of  the session of which its process group is a member.  (See cre‐
147       dentials(7).)
148
149       A session can have a controlling terminal.  At any time, one (and  only
150       one) of the process groups in the session can be the foreground process
151       group for the terminal; the remaining process groups are in  the  back‐
152       ground.   If  a signal is generated from the terminal (e.g., typing the
153       interrupt key to generate SIGINT), that signal is  sent  to  the  fore‐
154       ground process group.  (See termios(3) for a description of the charac‐
155       ters that generate signals.)  Only the  foreground  process  group  may
156       read(2)  from  the  terminal;  if  a  background process group tries to
157       read(2) from the terminal, then the group is  sent  a  SIGTTIN  signal,
158       which  suspends  it.   The  tcgetpgrp(3) and tcsetpgrp(3) functions are
159       used to get/set the foreground process group of the controlling  termi‐
160       nal.
161
162       The  setpgid() and getpgrp() calls are used by programs such as bash(1)
163       to create process groups in order to implement shell job control.
164
165       If the termination of a process causes a process group  to  become  or‐
166       phaned,  and  if  any  member  of  the  newly orphaned process group is
167       stopped, then a SIGHUP signal followed by a SIGCONT signal will be sent
168       to  each  process  in  the  newly  orphaned process group.  An orphaned
169       process group is one in which the parent of  every  member  of  process
170       group  is either itself also a member of the process group or is a mem‐
171       ber of a process  group  in  a  different  session  (see  also  creden‐
172       tials(7)).
173