#include <stdio.h>      /* For printing output       */
#include <signal.h>     /* for kill()                */
#include <unistd.h>     /* for getppid() and sleep() */
#include <sys/types.h>  /* for pid_t variable type   */

int main(int argc, char *argv[])
{
     int i;
     pid_t parent;

     /* To make this program exit from the shell it was
      * started from, we need to kill the parent
      * process of the process that is running this
      * program.
      *
      * Our parent process is the process (probably
      * a shell) that started this program.
      */

     /* get the process ID (PID) of our parent */
     parent = getppid();

     /* Countdown */
     printf("\nLogging out in 5 seconds: ");
     for (i = 5; i > 0; --i) {
	  fflush(stdout);
	  sleep(1);
	  printf("%d ", i);
     }
     fflush(stdout);
     printf("  GO!\n");
     sleep(1);

     /* Use USR1 signal, because the shell ignores the
      * QUIT and TERM.  As KILL and STOP are to strong
      * for this purpose, and QUIT or ABRT would cause
      * a core dump, we best chose USR1, USR2 or HUP
      */
     if (kill(parent, SIGHUP) < 0) {
	  /* If kill() returns -1, we were not able
	   * to kill the parent. So print an error
	   * message to stderr.
	   */
	  perror(argv[0]);  /* also mention program name */
	  return 1;
     }
     return 0;
}