# setpgid

## NAME



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


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## 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 */
           **[[deprecated]] pid_t getpgrp(pid_t** _pid_**);** /* BSD version */
    
           **int setpgrp(void);** /* System V version */
           **[[deprecated]] 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**()).
    
           **EPERM** The target process group does not exist.  (**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.
    


## STANDARDS



           **getpgid**()
           **setpgid**()
           **getpgrp**() (no args)
           **setpgrp**() (no args)
                  POSIX.1-2008 (but see HISTORY).
    
           **setpgrp**() (2 args)
           **getpgrp**() (1 arg)
                  None.
    


## 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)).
    


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