#include <termios.h> pid_t tcgetsid(int fildes);
The tcgetsid() function obtains the process group ID of the session for which the terminal specified by fildes is the controlling terminal.
Upon successful completion, tcgetsid() returns the process group ID associated with the terminal. Otherwise, a value of (pid_t)−1 is returned and errno is set to indicate the error.
The tcgetsid() function will fail if:
The fildes argument is not associated with a controlling terminal.
The fildes argument is not a valid file descriptor.
The file associated with fildes is not a terminal.
See attributes(5) for descriptions of the following attributes: