A deadman's switch in C for a cronjob

deadman.c

/**
 Original Request:
 
 ****
 A dead man's switch is a switch that is automatically operated if the human operator 
 becomes incapacitated, such as through death, loss of consciousness, or being bodily 
 removed from control. Originally applied to switches on a vehicle or machine, it has 
 since come to be used to describe other intangible uses like in computer software. 
 In alerting systems such a control can be useful, for instance in the case that a 
 cron job or backup process doesn't complete.

In our case, let's assume that a cron job we want to monitor touches a file named 
/tmp/my_cron_job and updates the last modified time each time it runs.

Let's apply the concept to create a script that:

Takes as input two pieces of data: a file whose last modified time we will check 
and a TTL after we consider the cron job to have failed

Returns 0 for an ok status, 1 for an error condition

Example usage:

./dead_man_switch <file_to_check> <ttl>
****

My take:
	get file mtime
	if error then error 1(file gone or permission)
	diff = now-then
	if > ttl then error 1
	if < ttl then not error 0

compile it:
	gcc deadman.c -o deadman

run it:
	./deadman deadman.c 360
	
	// to see values for fun you can do:
	./deadman deadman.c 360 d

**/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <stdbool.h>
#include <sys/stat.h>
#include <sys/types.h>

const char *path_file = NULL;

int main(int argc, char* argv[]) {
	if (!(argc > 2 && argc < 5)) {
		fprintf(stderr, "usage: deadman path MAX_ttl_in_secs [dryrun]\n");
		return -1;
	}

	// quick vars
	time_t now = time(NULL);
	struct stat attr;
	long ttl_seconds = 0;
	bool dryrun = false;

	// dangerous stuff here
	path_file = argv[1];
	ttl_seconds = atol(argv[2]);

	if(argv[3]!=NULL) dryrun = true;

	// if ttl_seconds > diff return 0 - good status
	// otherwise return 1 (file missing, ttl_seconds>diff) - bad status
	if (!stat(path_file, &attr)) {
		// unnecessary casting for darwinbs 
		long diff = (long)now - (long)attr.st_mtime;

		// validate the logics
		if(dryrun) {
			printf("path: %s \n", path_file);
			printf("now : %ld \n", now);
			printf("then: %ld \n", attr.st_mtime);
			printf("diff: %ld \n", diff);
			if(diff < ttl_seconds) printf("ok 1 \n");
			else printf("not ok 0 \n");
		}

		// actual logics heh shortcut 1 second because reasons
		if(diff < ttl_seconds) return 0;
		else return 1;
	} else {
		if(dryrun) {
			printf("path: %s \n", path_file);
			printf("statd error (not found or other) return 1 \n");
		}
		return 1;
	}
}