s - seconds (default)
m - minutes
h - hours
d - days

DESCRIPTION
       --preserve-status
              以與COMMAND相同的狀態(tài)退出，即使命令超時

       --foreground
              當(dāng)不直接從shell提示符運行超時時，允許COMMAND從TTY讀取并獲得TTY信號；在此模式下，COMMAND的子級不會超時

       -k, --kill-after=DURATION
              如果COMMAND仍在運行，也發(fā)送KILL信號在發(fā)出初始信號后很久

       -s, --signal=SIGNAL

              指定超時時要發(fā)送的信號；SIGNAL可以是類似“HUP”的名稱或數(shù)字；有關(guān)信號列表，請參見“kill-l”

       --help
              顯示此幫助并退出 

       --version
              輸出版本信息并退出

...
int main(int argc, char** argv) {
...
    for(int i=1;i<argc;i++) {
    	char* arg = argv[i];
    	if(strlen(arg) <= 0) continue;
    	
    	if(arg[0] == '-') {
			if(!strcmp(arg, "-h") || !strcmp(arg, "--help")) {
				printHelp(argv[0]);
				return EXIT_SUCCESS;
			} else if(!strcmp(arg, "-9") || !strcmp(arg, "--kill")) {
				sig_kill = SIGKILL;
	...
			} else {
				fprintf(stderr, "Illegal argument: %s\n", arg);
				return EXIT_FAILURE;
			}
    	} else {
			/* 
			沒有更多選項。檢查是否有足夠的剩余參數(shù)
			基本語法是/程序[OPTIONS]超時程序[ARGS]
			而超時和程序是強(qiáng)制性的  */
    		if (i+2 > argc) {		// 檢查是否給出超時和程序
				fprintf(stderr, "Not enough arguments. Check %s --help, if you need help\n", argv[0]);
				if(i+1 > argc) {
					// 檢查參數(shù)是否為數(shù)字
					fprintf(stderr, "  Missing: TIMEOUT PROGRAM\n");
				} else {
					if(is_numeric(argv[i]))
						fprintf(stderr, "  Missing: PROGRAM\n");
					else
						fprintf(stderr, "  Missing: TIMEOUT\n");
				}
				return EXIT_FAILURE;
    		} else {
				int seconds = atoi(argv[i]);
				if(seconds < 0) {
					fprintf(stderr, "Timeout cannot be negative");
					return EXIT_FAILURE;
				}
				timeout = (unsigned int)seconds;
				
				// 合并程序和可選程序參數(shù)
				for(int j=i+1;j<argc;j++)
					command = strappend(command, argv[j]);
				
				break;
			}
    	}
    	
    }
    
    // 檢查程序參數(shù)
	if(command == NULL || strlen(command) <= 0) {
		fprintf(stderr, "Not enough arguments. Check %s --help, if you need help\n", argv[0]);
		fprintf(stderr, "  Missing: TIMEOUT PROGRAM\n");
		return EXIT_FAILURE;
	}
    
    // Fork守護(hù)程序（如果需要）
    if (daemonize) {
    	fork_daemon();
    }
    
    
    ...

		int status;
		pid_t wait_status;
		
		// 信號處理器
		signal(SIGINT, sig_handler);
		signal(SIGTERM, sig_handler);
		signal(SIGALRM, sig_handler);
		
		if(verbose) printf("Child process forked with pid %d.\n", proc_pid);
		
		// 設(shè)置報警
		if(timeout > 0) alarm(timeout);
		wait_status = waitpid(proc_pid, &status, 0);		// Wait for child
		runtime += millis();
		if(wait_status < 0) {
			fprintf(stderr, "Error waiting for process: %s\n", strerror(errno));
			return EXIT_FAILURE;
		}
		status = WEXITSTATUS(status);		// 獲取實際退出狀態(tài)
		if(status != 0) {
			if(verbose) fprintf(stderr, "Process exited with status %d after %ld milliseconds\n", status, runtime);
			return status;
		} else {
			if(verbose) printf("Process completed after %ld milliseconds\n", runtime);
			return status;
		}
	}
    
    ...
}
...
static void sig_handler(int sig_no) {
	switch(sig_no) {
		case SIGALRM:
			// Timeout
			if(verbose)
				printf("TIMEOUT after %ld milliseconds.\n", runtime+millis());
			else
				printf("TIMEOUT\n");
			terminate_process();
			exit(EXIT_FAILURE);
			break;
		case SIGINT:
		case SIGTERM:
			if(proc_pid <= 0) exit(EXIT_FAILURE);
			if(verbose) printf("Program termination request\n");
			if(proc_pid > 0) kill(proc_pid, sig_no);
			exit(EXIT_FAILURE);
			return;
	}
}

...

30 9 * * * timeout -s SIGKILL 12h /home/pirate/programs/hadoop/bin/hdfs balancer -threshold 10  > ~/balancer-stdout.log 2>~/balancer-stderr.log & 
32 9 * * * /home/pirate/programs/hadoop/bin/hdfs dfsadmin -setBalancerBandwidth 304857600