#include <stdio.h>#include <unistd.h>#include <stdlib.h>#include <signal.h>#include <sys/types.h>#include <sys/wait.h>pid_t pid;void sig_handler(int signum,siginfo_t *info,void *notused){	if (signum == SIGCHLD) 		printf("process id %d\n",info->si_pid);}int main(){	struct sigaction newact,oldact;		newact.sa_sigaction = sig_handler;	sigemptyset(&newact.sa_mask);	newact.sa_flags = SA_SIGINFO;		sigaction(SIGCHLD,&newact,&oldact);	if ((pid = fork()) < 0)		perror("fork failed\n");	if (pid) {		printf("father id %d\n",getpid());		/* father process */		while (1);	} else {		/* child process */		sleep(2);		printf("child id %d\n",getpid());	}	return 0;}