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man:getpgid

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
     existing 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
     exposed 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
     exposed  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
     returned, 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
     orphaned, 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

     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.

Linux 2017-09-15 SETPGID(2)

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