WordPress 4.3 was released couple of days back. Every new release brings along with it some new features and few issues as well. If you are using FTP/SSH2 method for the plugin and theme updates on your WP installation, chances are that post 4.3, you cannot update them anymore and are getting the following error every time you try to do so.
The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions.
WordPress has acknowledged the issue which happened because 4.3 introduces a check to see if the file is writable or not. This is done via is_writable() PHP function. But the PHP function itself is not perfect as it does not check for ownership of the file while performing the check and end up returning false even if the file is writable. While WordPress team has promised that a fix for this would be shipped in 4.3.1 version, meanwhile you can use any of the following two methods to get around the problem.
- Install SFTP/SSH Update Support plugin. This plugin bypasses the SSH2 method completely and should bring back the functionality. You just need to install it to fix the issue. There are no settings to configure.
- Apply this patch which fixes the issue for now i.e. replace the file wp-admin/includes/class-wp-filesystem-ssh2.php with the file from here. Since the next WP update is going to carry the fix, updating the core file at this time shouldn’t be a problem at all and can be done safely.
That’s it. Report if you are still facing any problems.