trusty (3) setsid.3posix.gz

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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>


       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 .