Pb change permission certificat SSL

Hi,

I can't change the permission to the SSL certificate

root@vm1jh:~# chmod 400 /etc/pve/local/pve-ssl.*
chmod: changing permissions of `/etc/pve/local/pve-ssl.key': Function not implemented
chmod: changing permissions of `/etc/pve/local/pve-ssl.pem': Function not implemented



For the security i want olny acces by root

bet regards