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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  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 cre-
       dentials(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 pro-
       cess 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 pro-
              cess 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  ses-
       sion  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 sig-
       nals.)  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 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 followed by a SIGCONT signal will be sent to each process in the
       newly orphaned process 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 informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-08-06                        SETPGID(2)