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

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

SYNOPSIS
       #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 <= 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 to indicate the error.

       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 to indicate the error.

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 ter‐
       minal; 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)

Linux                                                                          2021-03-22                                                                     SETPGID(2)