setpgid

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

NAME
       setpgid, getpgid, setpgrp, getpgrp - set/get process group

SYNOPSIS
       #include <sys/types.h>
       #include <unistd.h>

       int setpgid(pid_t pid, pid_t pgid);
       pid_t getpgid(pid_t pid);

       pid_t getpgrp(void);                 /* POSIX.1 version */
       pid_t getpgrp(pid_t pid);            /* BSD version */

       int setpgrp(void);                   /* System V version */
       int setpgrp(pid_t pid, pid_t pgid);  /* BSD version */

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getpgid():
           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

       setpgrp() (POSIX.1):
           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _SVID_SOURCE

       setpgrp() (BSD), getpgrp() (BSD):
           [These are available only before glibc 2.19]
           _BSD_SOURCE &&
               ! (_POSIX_SOURCE || _POSIX_C_SOURCE || _XOPEN_SOURCE ||
                   _GNU_SOURCE || _SVID_SOURCE)

DESCRIPTION
       All  of  these interfaces are available on Linux, and are used for get-
       ting and setting the process group ID (PGID) of a  process.   The  pre-
       ferred,  POSIX.1-specified  ways  of doing this are: getpgrp(void), for
       retrieving the calling process's PGID; and  setpgid(),  for  setting  a
       process's PGID.

       setpgid()  sets  the  PGID of the process specified by pid to pgid.  If
       pid is zero, then the process ID of the calling process  is  used.   If
       pgid is zero, then the PGID of the process specified by pid is made the
       same as its process ID.  If setpgid() is used to move  a  process  from
       one  process  group to another (as is done by some shells when creating
       pipelines), both process groups must be part of the same  session  (see
       setsid(2) and credentials(7)).  In this case, the pgid specifies an ex-
       isting process group to be joined and the session ID of that group must
       match the session ID of the joining process.

       The POSIX.1 version of getpgrp(), which takes no arguments, returns the
       PGID of the calling process.

       getpgid() returns the PGID of the process specified by pid.  If pid  is
       zero,  the  process ID of the calling process is used.  (Retrieving the
       PGID of a process other than the caller is rarely  necessary,  and  the
       POSIX.1 getpgrp() is preferred for that task.)

       The  System V-style  setpgrp(), which takes no arguments, is equivalent
       to setpgid(0, 0).

       The BSD-specific setpgrp() call, which takes arguments pid and pgid, is
       a wrapper function that calls

           setpgid(pid, pgid)

       Since  glibc 2.19, the BSD-specific setpgrp() function is no longer ex-
       posed by <unistd.h>; calls should be replaced with the  setpgid()  call
       shown above.

       The  BSD-specific getpgrp() call, which takes a single pid argument, is
       a wrapper function that calls

           getpgid(pid)

       Since glibc 2.19, the BSD-specific getpgrp() function is no longer  ex-
       posed by <unistd.h>; calls should be replaced with calls to the POSIX.1
       getpgrp() which takes no arguments (if the  intent  is  to  obtain  the
       caller's PGID), or with the getpgid() call shown above.

RETURN VALUE
       On  success,  setpgid() and setpgrp() return zero.  On error, -1 is re-
       turned, and errno is set appropriately.

       The POSIX.1 getpgrp() always returns the PGID of the caller.

       getpgid(), and the BSD-specific getpgrp() return  a  process  group  on
       success.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EACCES An attempt was made to change the process group ID of one of the
              children of the calling process and the child had  already  per-
              formed an execve(2) (setpgid(), setpgrp()).

       EINVAL pgid is less than 0 (setpgid(), setpgrp()).

       EPERM  An  attempt was made to move a process into a process group in a
              different session, or to change the process group ID of  one  of
              the  children of the calling process and the child was in a dif-
              ferent session, or to change the process group ID of  a  session
              leader (setpgid(), setpgrp()).

       ESRCH  For  getpgid():  pid does not match any process.  For setpgid():
              pid is not the calling process and not a child  of  the  calling
              process.

CONFORMING TO
       setpgid()  and  the  version  of getpgrp() with no arguments conform to
       POSIX.1-2001.

       POSIX.1-2001 also specifies getpgid() and the version of setpgrp() that
       takes  no  arguments.  (POSIX.1-2008 marks this setpgrp() specification
       as obsolete.)

       The version of getpgrp() with one argument and the version of setpgrp()
       that  takes  two arguments derive from 4.2BSD, and are not specified by
       POSIX.1.

NOTES
       A child created via fork(2) inherits its  parent's  process  group  ID.
       The PGID is preserved across an execve(2).

       Each  process group is a member of a session and each process is a mem-
       ber of the session of which its process group is a member.   (See  cre-
       dentials(7).)

       A  session can have a controlling terminal.  At any time, one (and only
       one) of the process groups in the session can be the foreground process
       group  for  the terminal; the remaining process groups are in the back-
       ground.  If a signal is generated from the terminal (e.g.,  typing  the
       interrupt  key  to  generate  SIGINT), that signal is sent to the fore-
       ground process group.  (See termios(3) for a description of the charac-
       ters  that  generate  signals.)   Only the foreground process group may
       read(2) from the terminal; if  a  background  process  group  tries  to
       read(2)  from  the  terminal,  then the group is sent a SIGTTIN signal,
       which suspends it.  The tcgetpgrp(3)  and  tcsetpgrp(3)  functions  are
       used  to get/set the foreground process group of the controlling termi-
       nal.

       The setpgid() and getpgrp() calls are used by programs such as  bash(1)
       to create process groups in order to implement shell job control.

       If  the  termination  of a process causes a process group to become or-
       phaned, and if any member  of  the  newly  orphaned  process  group  is
       stopped, then a SIGHUP signal followed by a SIGCONT signal will be sent
       to each process in the  newly  orphaned  process  group.   An  orphaned
       process  group  is  one  in which the parent of every member of process
       group is either itself also a member of the process group or is a  mem-
       ber  of  a  process  group  in  a  different  session (see also creden-
       tials(7)).

SEE ALSO
       getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3),  termios(3),  creden-
       tials(7)

COLOPHON
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Linux                             2017-09-15                        SETPGID(2)