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

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

9       #include <unistd.h>
10
11       int setpgid(pid_t pid, pid_t pgid);
12       pid_t getpgid(pid_t pid);
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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 */
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20   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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22       getpgid(): _XOPEN_SOURCE >= 500
23       setpgrp() (POSIX.1): _SVID_SOURCE || _XOPEN_SOURCE >= 500
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25       setpgrp() (BSD), getpgrp() (BSD): _BSD_SOURCE && ! (_POSIX_SOURCE ||
26       _POSIX_C_SOURCE || _XOPEN_SOURCE || _XOPEN_SOURCE_EXTENDED ||
27       _GNU_SOURCE || _SVID_SOURCE)
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DESCRIPTION

30       All  of  these interfaces are available on Linux, and are used for get‐
31       ting and setting the process group ID (PGID) of a  process.   The  pre‐
32       ferred,  POSIX.1-specified  ways  of doing this are: getpgrp(void), for
33       retrieving the calling process's PGID; and  setpgid(),  for  setting  a
34       process's PGID.
35
36       setpgid()  sets  the  PGID of the process specified by pid to pgid.  If
37       pid is zero, then the process ID of the calling process  is  used.   If
38       pgid is zero, then the PGID of the process specified by pid is made the
39       same as its process ID.  If setpgid() is used to move  a  process  from
40       one  process  group to another (as is done by some shells when creating
41       pipelines), both process groups must be part of the same  session  (see
42       setsid(2)  and  credentials(7)).   In  this case, the pgid specifies an
43       existing process group to be joined and the session ID  of  that  group
44       must match the session ID of the joining process.
45
46       The POSIX.1 version of getpgrp(), which takes no arguments, returns the
47       PGID of the calling process.
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49       getpgid() returns the PGID of the process specified by pid.  If pid  is
50       zero,  the  process ID of the calling process is used.  (Retrieving the
51       PGID of a process other than the caller is rarely  necessary,  and  the
52       POSIX.1 getpgrp() is preferred for that task.)
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54       The  System  V-style setpgrp(), which takes no arguments, is equivalent
55       to setpgid(0, 0).
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57       The BSD-specific setpgrp() call, which takes arguments pid and pgid, is
58       equivalent to setpgid(pid, pgid).
59
60       The  BSD-specific getpgrp() call, which takes a single pid argument, is
61       equivalent to getpgid(pid).
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RETURN VALUE

64       On success, setpgid() and setpgrp()  return  zero.   On  error,  -1  is
65       returned, and errno is set appropriately.
66
67       The POSIX.1 getpgrp() always returns the PGID of the caller.
68
69       getpgid(),  and  the  BSD-specific  getpgrp() return a process group on
70       success.  On error, -1 is returned, and errno is set appropriately.
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ERRORS

73       EACCES An attempt was made to change the process group ID of one of the
74              children  of  the calling process and the child had already per‐
75              formed an execve(2) (setpgid(), setpgrp()).
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77       EINVAL pgid is less than 0 (setpgid(), setpgrp()).
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79       EPERM  An attempt was made to move a process into a process group in  a
80              different  session,  or to change the process group ID of one of
81              the children of the calling process and the child was in a  dif‐
82              ferent  session,  or to change the process group ID of a session
83              leader (setpgid(), setpgrp()).
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85       ESRCH  For getpgid(): pid does not match any process.   For  setpgid():
86              pid  is  not  the calling process and not a child of the calling
87              process.
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CONFORMING TO

90       setpgid() and the version of getpgrp() with  no  arguments  conform  to
91       POSIX.1-2001.
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93       POSIX.1-2001 also specifies getpgid() and the version of setpgrp() that
94       takes no arguments.  (POSIX.1-2008 marks this  setpgrp()  specification
95       as obsolete.)
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97       The version of getpgrp() with one argument and the version of setpgrp()
98       that takes two arguments derive from 4.2BSD, and are not  specified  by
99       POSIX.1.
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NOTES

102       A  child  created  via  fork(2) inherits its parent's process group ID.
103       The PGID is preserved across an execve(2).
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105       Each process group is a member of a session and each process is a  mem‐
106       ber of the session of which its process group is a member.
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108       A  session can have a controlling terminal.  At any time, one (and only
109       one) of the process groups in the session can be the foreground process
110       group  for  the terminal; the remaining process groups are in the back‐
111       ground.  If a signal is generated from the terminal (e.g.,  typing  the
112       interrupt  key  to  generate  SIGINT), that signal is sent to the fore‐
113       ground process group.  (See termios(3) for a description of the charac‐
114       ters  that  generate  signals.)   Only the foreground process group may
115       read(2) from the terminal; if  a  background  process  group  tries  to
116       read(2)  from  the  terminal,  then the group is sent a SIGTSTP signal,
117       which suspends it.  The tcgetpgrp(3)  and  tcsetpgrp(3)  functions  are
118       used  to get/set the foreground process group of the controlling termi‐
119       nal.
120
121       The setpgid() and getpgrp() calls are used by programs such as  bash(1)
122       to create process groups in order to implement shell job control.
123
124       If  a  session has a controlling terminal, and the CLOCAL flag for that
125       terminal is not set, and a terminal hangup  occurs,  then  the  session
126       leader  is  sent  a SIGHUP.  If the session leader exits, then a SIGHUP
127       signal will also be sent to each  process  in  the  foreground  process
128       group of the controlling terminal.
129
130       If  the  exit of the process causes a process group to become orphaned,
131       and if any member of the newly orphaned process group is stopped,  then
132       a  SIGHUP  signal  followed  by  a  SIGCONT signal will be sent to each
133       process in the newly orphaned process group.  An orphaned process group
134       is  one  in which the parent of every member of process group is either
135       itself also a member of the process group or is a member of  a  process
136       group in a different session (see also credentials(7)).
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SEE ALSO

139       getuid(2),  setsid(2),  tcgetpgrp(3), tcsetpgrp(3), termios(3), creden‐
140       tials(7)
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COLOPHON

143       This page is part of release 3.25 of the Linux  man-pages  project.   A
144       description  of  the project, and information about reporting bugs, can
145       be found at http://www.kernel.org/doc/man-pages/.
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149Linux                             2009-09-20                        SETPGID(2)
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