I was working on a CentOS 7 server the other day that had a LAMP stack installed. It was used to host only a single instance of WordPress.
Upgrading themes and plugins from the admin interface worked fine, but curiously, WordPress core upgrades did not. Instead, WordPress was asking for FTP details every time, which also prevented auto upgrades from being installed.
This didn’t make any sense because there was no FTP server installed on the box, nor had there ever been one. But it did indicate that WordPress had an issue with overwriting core files.
The first thing I checked was that the /var/www/html directory had the correct file and ownership permissions. It all looked correct, even though I did manually set them again just to make sure. Without success. WordPress was still asking for FTP credentials.
After some research, I found that there is a setting for how WordPress accesses the filesystem when it’s upgrade time. We can define it with a constant called FS_METHOD in wp-config.php. The ins and outs are explained in the codex, under Upgrade Constants:
FS_METHOD forces the filesystem method. It should only be “direct”, “ssh2”, “ftpext”, or “ftpsockets”. Generally, you should only change this if you are experiencing update problems. If you change it and it doesn’t help, change it back/remove it. Under most circumstances, setting it to ‘ftpsockets’ will work if the automatically chosen method does not. Note that your selection here has serious security implications. If you are not familiar with them, you should seek help before making a change.
- (Primary Preference) “direct” forces it to use Direct File I/O requests from within PHP. It is the option chosen by default.
- (Secondary Preference) “ssh2” is to force the usage of the SSH PHP Extension if installed
- (3rd Preference) “ftpext” is to force the usage of the FTP PHP Extension for FTP Access, and finally
- (4th Preference) “ftpsockets” utilises the PHP Sockets Class for FTP Access.
So on this particular server, for whatever reason, WordPress did not choose the first method (direct), even though it should have. Defining this constant manually did the trick, all I had to do was add this line to my wp-config.php file:
// explicitly use direct mode and stop asking for FTP details define('FS_METHOD','direct');
Now updates are working as expected. I’ve never seen this problem on LAMP stacks before. Guess you learn something new every day.