returns the session ID of the current session that has the
terminal associated to
as controlling terminal.
This terminal must be the controlling terminal of the calling process.
refers to the controlling terminal of our session,
will return the session ID of this session.
Otherwise, -1 is returned, and
is set appropriately.
is not a valid file descriptor.
The calling process does not have a controlling terminal, or
it has one but it is not described by
is provided in glibc since version 2.1.
This function is implemented via the
since Linux 2.1.71.