SETSID(3)                  POSIX Programmer's Manual                 SETSID(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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.1-2017 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.1-2017, <sys_types.h>, <unistd.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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 .



IEEE/The Open Group                  2017                            SETSID(3)
