How to tell what the error is on my website when PHP can't change flag in a file?

Question

Related to a student enrollment website, I have a PHP file that runs at 5:00 AM every morning to check for the students who haven't paid the fees. If the student hasn't paid the fees, they are dropped from the class. This file is called dropstudent.php and this is the folder hierarchy:

cronjobs/
|
|- dropstudent.php
|- flag.txt

The flag.txt file contains just one word - either true or false . Students can only pay the fees (which is handled in a PHP file elsewhere on the website) if the flag is set to true.

Now, before we drop the students, we set the flag to false, perform the checks and perform the necessary drops. In the end, we set this flag back to true.

So far, this was working just fine and no one touched this code. But recently, we have been having complaints about students not being able to pay. I looked into it and it turns out that the step where we are resetting the flag to true is not working since the flag gets changed to false but doesn't return to true.

Here is my code:

#!/opt/rh/php55/root/usr/bin/php

<?php

// require '../dbmanage.php';
require '/path to college servers/dbmanage.php';

logCronJob("dropstudent", "begin");

$filepath = '/path to college servers/cronjobs/flag.txt';

// Change flag to false
$myfile = fopen($filepath, "w") or die("Unable to open file!");
$txt = "false";
fwrite($myfile, $txt);

// do the drop checks and other relevant stuff here

// Change flag back to true
$myfile = fopen($filepath, "w") or die("Unable to open file!");
$txt = "true";
fwrite($myfile, $txt);
fclose($myfile);

It would be great if someone can tell me how to figure out what is wrong here, and what can I do to fix it. I can post more detailed code (the checks and drop) if needed.

Answer 1

You need to call fclose($myfile); after you do the first fwrite() , to ensure that the buffer is flushed. The way you've written it, the first stream won't be closed until the script ends. At that time it will flush its buffer, overwriting what was written by the second stream.

It would be simpler if you used file_put_contents() . It opens, writes, and closes the file in one step:

#!/opt/rh/php55/root/usr/bin/php

<?php

// require '../dbmanage.php';
require '/path to college servers/dbmanage.php';

logCronJob("dropstudent", "begin");

$filepath = '/path to college servers/cronjobs/flag.txt';

// Change flag to false
file_put_contents("false", $filepath);

// do the drop checks and other relevant stuff here

// Change flag back to true
file_put_contents("true", $filepath);

Answer 2

I finally resolved the error. Here are the steps I followed and the error messages I received in between:

1. As @SulthanAllaudeen had suggested, I checked the error logs to find a "Permission Denied" error while opening flag.txt .
2. Talked to the administration regarding any recent changes in the permission or system upgrades. They hadn't made any changes.
3. Followed @Barmar's advice to close the file handle.
4. Still kept getting the same error.
5. Then changed the path to the flag.txt file from being relative to absolute . Turns out that cronjobs need all paths to be absolute, at least in my case.
6. This resolved the "Permission Denied" error. But then I started getting the error "cannot redeclare the function". So the emails.php file that I was including, I changed it to include_once() and it worked.
7. I am still following @Barmar's advice to close the file handle as a good practice.

TL;DR: Resolved the error by giving the absolute paths to all the files being included. Also, changed the include() statement to include_once().