A WordPress website hosted in Plesk shows the error: open_basedir restriction in effect

Symptoms

When opening a website in a web-browser or installing a WordPress plugin/theme at Plesk > WordPress > example.com > Plugins/Themes, the WordPress plugin/theme references to a non-existent path and, as a result, fails due to open_basedir restiriction:

open_basedir restriction in effect. File(/var/www/vhosts/example.com/public_html/wp-content/cache/wp-rocket/www.example.com/shop/index-https.html/index-https.html_gzip) is not within the allowed path(s): (/var/www/vhosts/example.com/:/tmp/) in /var/www/vhosts/example.com/public_html/wp-content/plugins/wp-rocket/inc/classes/Buffer/class-cache.php on line 96

Cause

The absolute path to the WordPress file is merged with the path to the plugin directory and, as a result, restricted by open_basedir PHP parameter.

Resolution

Contact the WordPress plugin/theme developer to fid out how to fix the path.

The solution below is an example of how the issue can be fixed. It may differ for different plugins and themes:

1. Log in to Plesk.

2. Go to Domains > example.com > File Manager.

3. Edit the file mentioned in the error. In this example, the file is  ...httpdocswp-includesl10n.php.

4. Find WP_PLUGIN_DIR and replace it with basename( dirname( __FILE__ ) ).
   Example:
   Original:

   $path = WP_PLUGIN_DIR . '/' . trim( $plugin_rel_path, '/' );

   Modified:

   $path = basename( dirname( __FILE__ ) );

5. Save changes.