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

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