get session ID associated with a controlling terminal
tcgetsid() function returns the value of the session
ID associated with the specified controlling terminal device. The session ID
is defined as the process group ID of the session leader.
If an error occurs,
tcgetsid() returns -1 and the global
variable errno is set to indicate the error, as follows:
- The fd argument is not a valid file descriptor.
- The calling process does not have a controlling terminal or the underlying
terminal device represented by fd is not the
tcgetsid() function is expected to be compliant with
the IEEE Std 1003.1-2008 (“POSIX.1”)
tcgetsid() function has been available since