static void

sig_hup(int signo)

{

        printf("SIGHUP received, pid = %d\n", getpid());

}



static void

pr_ids(char *name)

{

        printf("%s: pid = %d, ppid = %d, pgrp = %d, tpgrp = %d\n",

            name, getpid(), getppid(), getpgrp(), tcgetpgrp(STDIN_FILENO));

        fflush(stdout);

}

int

main(void)

{

        char    c;

        pid_t   pid;

        pr_ids("parent");

        if ((pid = fork()) < 0) {

                printf("fork error");

        }

        else if (pid > 0) {    

                sleep(5);              

                exit(0);                

        }

        else {                  

                pr_ids("child");

                signal(SIGHUP, sig_hup);        

              kill(getpid(), SIGTSTP);        

                pr_ids("child");        //这里调用pr_ids时，父进程已经关闭，但是调用printf却可以向原来的controlling terminal写

                if (read(STDIN_FILENO, &c, 1) != 1)        //但是这里向原来的terminal读却有问题

                        printf("read error from controlling TTY, errno = %d\n",

                            errno);          //这里也可以向原来的controlling terminal写

                exit(0);

        }

}