Unable to secure WordPress instance in Plesk: Permissions for files and directories still marked as Not Secure

Symptoms

• When clicking the Secure button in Plesk at Domains > example.com > Check Security nothing happens: There is still a red exclamation mark next to Permissions for files and directories.

• Unable to apply security measure "Restrict access to files and directories":

  PLESK_ERROR: Unable to set permissions on /var/www/vhosts/example.com/httpdocs/script.php: Operation not permitted

Cause

Incorrect ownership on files/directories under a domain document root directory.

Resolution

Files/directories under a domain document root directory should belong to psacln group and to the sysuser user. Set the correct ownership as follows:

1. Connect to the Plesk server using SSH.

2. Modify the ownership for all files and directories inside domain's document root:

   # plesk repair fs -y example.com

Note: the solution above is applicable for Plesk 17.8 and Plesk Obsidian. For other versions use the solution from this article: How to restore default permissions in the virtual host directory on Linux