SETSID(3P)						     POSIX Programmer's Manual							SETSID(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       setsid - create session and set process group ID

SYNOPSIS

       #include <unistd.h>

       pid_t setsid(void);

DESCRIPTION

       The setsid() function shall create a new session, if the calling process is not a process group leader. Upon  return  the  calling  process
       shall  be  the  session leader of this new session, shall be the process group leader of a new process group, and shall have no controlling
       terminal. The process group ID of the calling process shall be set equal to the process ID of the  calling  process.  The  calling  process
       shall be the only process in the new process group and the only process in the new session.

RETURN VALUE

       Upon successful completion, setsid() shall return the value of the new process group ID of the calling process.	Otherwise, it shall return
       (pid_t)-1 and set errno to indicate the error.

ERRORS

       The setsid() function shall fail if:

       EPERM  The calling process is already a process group leader, or the process group ID of a process other than the calling  process  matches
	      the process ID of the calling process.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       The  setsid()  function	is  similar  to  the setpgrp() function of System V.  System V, without job control, groups processes into process
       groups and creates new process groups via setpgrp(); only one process group may be part of a login session.

       Job control allows multiple process groups within a login session.  In order to limit job control actions so that they can only affect pro-
       cesses  in the same login session, this volume of IEEE Std 1003.1-2001 adds the concept of a session that is created via setsid(). The set-
       sid() function also creates the initial process group contained in the session.	Additional process groups can be created via the setpgid()
       function.   A  System  V  process group would correspond to a POSIX System Interfaces session containing a single POSIX process group. Note
       that this function requires that the calling process not be a process group leader. The usual way to ensure this is true is to create a new
       process	with  fork()  and  have it call setsid(). The fork() function guarantees that the process ID of the new process does not match any
       existing process group ID.

FUTURE DIRECTIONS

       None.

SEE ALSO

       getsid(), setpgid(), setpgrp(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/types.h>, <unistd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								SETSID(3P)