/* Forks and then the parent sends a signal to the child. The signal   */
/* sent is the command line argument. After this signal is sent, the   */
/* child resumes the endless loop. You'll get the system prompt.       */ 
/* Next, issue the kill command to the child (use 'ps xg' to get the   */
/* pid) with different arguments (except SIGKILL). Stop it for good    */
/* using kill -9 <pid>						       */

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#define  period 3

void handler(int);

main(argc,argv)
int argc;
char *argv[];
{pid_t ChildID;
 int i,flag=0;
 if (argc!=2) {
  fprintf(stderr,"Form: sigdemo <signal>\n");
  exit(1);
 }
 if ((ChildID=fork()) < 0) {
  perror("Fork!!!!");
  exit(1);
 }
 else if (ChildID) { /* Parent */
  fprintf(stderr,"Will Send Signal %d in %d Seconds \n",atoi(argv[1]),period);
  sleep(period);
  fprintf(stderr,"Parent: Sending Signal\n");
  kill(ChildID,atoi(argv[1]));
 }
 else {  /* Child */
  struct sigaction action;
  action.sa_handler = (void (*)(int))handler;
  for (i=1;i<32;i++) {
// if (signal(i,handler)==SIG_ERR) {	old way
   if (sigaction(i,&action,NULL)<0) {
    /* Do nothing. Try this: Write the signal number here so you can discern */
    /* which ones cause an error in the signal() call. Why are they an error?*/
   }
  }
  do {
   if (!flag && (getppid()==1)) {
    fprintf(stderr,"Parent Finished. Child's Parent now init\n");
    flag++;
   }
  } while(1);
 }
}
void handler(int sig)
{fprintf(stderr,"Child: Caught Signal %d\n",sig);
 //return(NULL);
}