The tcgetsid() function shall obtain the process group ID of
the session for which the terminal specified by
fildes is the controlling terminal.
Upon successful completion, tcgetsid() shall return the process
group ID associated with the terminal. Otherwise, a value
of (pid_t)-1 shall be returned and errno set to indicate
The tcgetsid() function shall fail if:
The fildes argument is not a valid file descriptor.
The calling process does not have a controlling terminal, or the file
is not the controlling terminal.
The following sections are informative.
The Base Definitions volume of IEEE Std 1003.1-2001, <termios.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