How do I give PHP write access to a directory?

I'm trying to use PHP to create a file, but it isn't working. I am assuming this is because it doesn't have write access (it's always been the problem before). I tried to test if this was the problem by making the folder chmod 0777, but that just ended up making every script in that directory return a 500 error message until I changed it back. How do I give PHP write access to my file system so it can a create a file?

Edit: It is hosted on Hostgator shared hosting using Apache.

Edit 2: Someone asked for the code: The code is a GD image script. I know the rest of it works as previously I was creating the image every ime it was called. Now I am trying to create them when new text is added and save them to a folder. The write line I have is: imagejpeg(null,$file,85);

I also created a test file to check if it was just a broken script (mainly copied from tizag): http://gearboxshow.info/rkr/lesig.jpg/testfile.txt (I don't know if/how to post the code here properly. Here is the contents of the PHP script, minus PHP tags.)

It returns 13,13,1 (separate lines), so it looks as if it thinks it wrote something, but the testfile.txt is blank (I uploaded a blank one), or non-existent (if I delete it).

Edit 3: The server runs CentOS.

Solution 1:

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.

Solution 2:

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 :)

Solution 3:

Simple 3-Step Solution

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

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.

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.

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.

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