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 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 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 Technology -- 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(P)