Website hosted in Plesk shows error 502 in the browser: AH01071: Got error 'Primary script unknown'

Symptoms

• Website displays the error 502 Bad Gateway.
• Under domain logs /var/www/vhosts/example.com/logs the following error can be found:

  CONFIG_TEXT: [proxy_fcgi:error] [pid 17521:tid 140525340448512] [client 35.181.112.20:0] AH01071: Got error 'Primary script unknown'

• Plesk utility plesk repair fs returns domain incorrect ownership.

  # There is incorrect ownership on some items in the WWW root directory
  of the domain 'example.com' ............................................ [ERROR]

Cause

Incorrect domain file permissions.

Resolution

1. Connect into the server via SSH

2. Fix the domain permissions with the following Plesk utility:

# plesk repair fs example.com -y

If issue is present on several domains, execute the following command instead:

# plesk repair fs -y