getpgrp

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 getting
       and setting the process group ID (PGID) of a process.  The preferred,
       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
              performed 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 different
              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 member
       of the session of which its process group is a member.  (See
       credentials(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
       background.  If a signal is generated from the terminal (e.g., typing the
       interrupt key to generate SIGINT), that signal is sent to the foreground
       process group.  (See termios(3) for a description of the characters 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 terminal.

       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 member of a
       process group in a different session (see also credentials(7)).

SEE ALSO
       getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3),
       credentials(7)

COLOPHON
       This page is part of release 5.08 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)