How do I give PHP write access to a directory?

Set the owner of the directory to the user running apache. Often nobody on linux

chown nobody:nobody <dirname>

This way your folder will not be world writable, but still writable for apache :)

An easy way is to let PHP create the directory itself in the first place.

<?php
 $dir = 'myDir';

 // create new directory with 744 permissions if it does not exist yet
 // owner will be the user/group the PHP script is run under
 if ( !file_exists($dir) ) {
     mkdir ($dir, 0744);
 }

 file_put_contents ($dir.'/test.txt', 'Hello File');

This saves you the hassle with permissions.

Simple 3-Step Solution

Abstract: You need to set the owner of the directory to the user that PHP uses (web server user).

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Step 1: Determine PHP User

Create a PHP file containing the following:

<?php echo `whoami`; ?>

Upload it to your web server. The output should be similar to the following:

www-data

Therefore, the PHP user is www-data.

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Step 2: Determine Owner of Directory

Next, check the details of the web directory via the command line:

ls -dl /var/www/example.com/public_html/example-folder

The result should be similar to the following:

drwxrwxr-x 2 exampleuser1 exampleuser2 4096 Mar 29 16:34 example-folder

Therefore, the owner of the directory is exampleuser1.

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Step 3: Change Directory Owner to PHP User

Afterwards, change the owner of the web directory to the PHP user:

sudo chown -R www-data /var/www/example.com/public_html/example-folder

Verify that the owner of the web directory has been changed:

ls -dl /var/www/example.com/public_html/example-folder

The result should be similar to the following:

drwxrwxr-x 2 www-data exampleuser2 4096 Mar 29 16:34 example-folder

Therefore, the owner of example-folder has successfully been changed to the PHP user: www-data.

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Done! PHP should now be able to write to the directory.