Unable to access File Manager for a certain domain or for all domains on a server: Permission denied

Symptoms

Unable to access File Manager for a certain domain or for all domains on a server:

Internal error: Unable to find the directory /var/www/vhosts/example.com/: filemng failed: filemng: opendir failed: Permission denied System error 13: Permission denied

Message Unable to find the directory /var/www/vhosts/example.com/: filemng failed: filemng: opendir failed: Permission denied System error 13: Permission denied
File    FileManagerController.php
Line    1054
Type    PleskUtilException

Also, it is not possible to connect to this domain using FTP:

Unable to connect FTP :
421 Service not available, remote server has closed.

Cause

Incorrect permissions on domain's folder.

Resolution

1. Connect to the server using SSH .
2. Run the following command to repair file permissions by Plesk:

   # plesk repair fs example.com
   Checking virtual hosts' file system
   There are files or directories with suspicious permissions in the
   root directory of the domain 'example.com' ..................... [WARNING]

3. Correct the permissions for the affected folder and its , setting the system user and Plesk service group:

   # chown -R System_User.psaserv /var/www/vhosts/example.com/httpdocs/
   # chown -R System_User.psaserv  /var/www/vhosts/example.com/error_docs/
   # chown -R System_User.psaserv  /var/www/vhosts/example.com/web_users/
   # chown -R System_User.root  /var/www/vhosts/example.com/logs

   where
   System_User - system user (main user) of the subscription that should be the same as shown in Plesk > Domains > example.com

4. Check permissions again and OK message should be displayed:

   # plesk repair fs -verbose example.com
   Checking virtual hosts' file system ................................. [OK]
   Error messages: 0; Warnings: 0; Errors resolved: 0