One of the nice features about WordPress is its ability to upgrade and install plugins on the fly. This is nice because now you don’t need to be bothered with the hassle of downloading plugins, unzipping their contents, and transferring them to your web server.

Unfortunately, the way in which WordPress determines if it has the appropriate permissions to upgrade plugins is implemented poorly. When WordPress doesn’t think it has permission, the admin panel will instead prompt you for FTP login information. This is a problem because sometimes WordPress will do this falsely even if it does have proper permissions.

The Problem

The way WordPress tries to guess if it has proper permissions is very primitive. Instead of using PHP’s is_writable, WordPress instead compares the web server’s User ID with the User ID of the wp-content directory’s owner*. While this might work for a large number of cases, it doesn’t work in all of them (including mine).

* It’s actually slightly more complicated than this, but the effect is the same.

The Environment

I run WordPress 3.x on Ubuntu 10.04 LTS under Lighttpd and PHP5-cgi. Lighttpd runs as user www-data and group www-data. If I wanted to let WordPress’ auto-detection of permissions work, I would have to change the owner of my website directories to www-data. This doesn’t fly with me, because I also want my user to have easy access to my document root and don’t like the idea of my data being user-owned by my webserver user.

The Solution

Instead of bending over to WordPress’ permission issues, I was able to perform the following simple steps to have auto-installing/updating plugins and themes *without *changing user ownership of my web files.

1. sudo chgrp -R www-data /path/to/wp/wp-content

   This changes group ownership of wp-content and all sub-directories to be group-owned by your webserver user. wp-content is where WordPress stores plugins, themes, cache files, and (AFAIK) file uploads.

2. sudo chmod -R g+w /path/to/wp/wp-content

   This makes wp-content and all of its sub-directories group-writable.

3. sudo chmod g+s /path/to/wp/wp-content

   This, g+s, is known as setgid. This causes newly-created files to be group-owned by wp-content’s owning group, in this case www-data.

4. Finally, add the following to the bottom of wp-config.php. This is an override built into the WordPress code. For more information, take a look at wp-admin/includes/file.php’s function get_filesystem_method.

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/* Force direct file updating
- http://www.charleshooper.net/blog/wordpress-auto-upgrade-and-dumb-permissions/
*/
define('FS_METHOD', 'direct');

So there you have it. WordPress does a poor job of properly detecting file permissions and, in some cases, needs to be overridden. If you’re still having problems after this, let me know and I will do my best to help you.