The Synology NAS or Network Attached Storage is base on Linux but it doesn’t have a “passwd” command as usually Linux system to change Synology NAS user or root password. If you want to change user or root password of Synology NAS you need to use “synouser” command instead of “passwd” as below example.

synouser --setpw admin yourpassword

Please note that we can’t change on root user. We need to change admin password instead of root and you will able to use that password to login as root.