Not working fopen() function in PHP (Apache, Linux Mint)

Question

fopen() does not work on my apache2 local server on Linux Mint

<?php
    error_reporting(E_ALL);
    ini_set('display_errors',1);
    include_once "c&f.php";

    fopen("test.txt", 'w');

The file

test.txt is created and I can open it using Sublime and write to it. The directory for this particular project is /var/www/site02. When configuring apache2 after installation, I specifically changed the ownership of this specific directory (site02) to be able to read and write files (sudo chown $USER:$USER -R ... you get the idea). In fact, I can indeed read and write with my user account in this directory (I can freely use cli git commands in this directory without "sudo").

If I access index.php using the code mentioned above, I get the following error:

"Warning: fopen(test.txt): Unable to open stream: Permission denied in /var/www/site02/index.php, line 6"

What happened? I've tried googling the problem but got thousands of different reasons, which only confused me more. Is the problem a problem with the apache server? Or do I need to make some configuration changes to PHP?

Answer 1

So, after posting this question, I decided to open /var/www/site02 with a file manager (Thunar) to check the permissions under the graphical interface. Yes, the owner of this directory is me and I can read and write. The group is myusername, and the permissions are also read and write. But for "others" there is only one permission: read. I changed it to read and write. And test it with some code:

$fh = fopen("test.txt", 'w') or die("error writing the file");

    $text = <<<_END
    line 1
    line 2
    line 3
    _END;

    fwrite($fh, $text) or die("error writing the file");
    fclose($fh);
    echo "成功！";

And it worked!