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 .