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 (con-
       sult the corresponding 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.  Other-
       wise, 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  processes 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 setsid() 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  call-
       ing  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 Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    SETSID(3P)