PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult 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. Otherwise, it shall return −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  POSIX.1‐2008  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 POSIX.1‐2008, <sys_types.h>, <unistd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications  Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
       and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .