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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(psid_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
       setpgrp() (POSIX.1): _SVID_SOURCE || _XOPEN_SOURCE >= 500

       setpgrp() (BSD), getpgrp() (BSD): _BSD_SOURCE && ! (_POSIX_SOURCE ||
       _POSIX_C_SOURCE || _XOPEN_SOURCE || _XOPEN_SOURCE_EXTENDED || _GNU_SOURCE ||
       _SVID_SOURCE)

DESCRIPTION
       All  of  these interfaces are available on Linux, and are used for getting and set-
       ting 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  ses-
       sion  (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  equivalent
       to setpgid(pid, pgid).

       The  BSD-specific  getpgrp() call, which takes a single pid argument, is equivalent
       to getpgid(pid).

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.

       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  termi-
       nal,  then the group is sent a SIGTSTP 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 a session has a controlling terminal, and the CLOCAL flag for that  terminal  is
       not  set,  and  a terminal hangup occurs, then the session leader is sent a SIGHUP.
       If the session leader exits, then a SIGHUP signal will also be sent to each process
       in the foreground process group of the controlling terminal.

       If  the  exit  of the process causes a process group to become orphaned, and if any
       member of the newly orphaned process group is stopped, then a  SIGHUP  signal  fol-
       lowed  by  a SIGCONT signal will be sent to each process in the newly orphaned pro-
       cess group.

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

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2008-08-06                        SETPGID(2)

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