Synology's OS doesn't seem to have a passwd command, and I have been unable to change my Root user's password using the synouser command:
MyNas > synouser --setpw root hunter2
Lastest SynoErr=[user_set.c:1040]
synouser.c:616 SYNOUserSet failed. synoerr=[0x1D00]
I found this thread with the same error message, but I don't want to install sudo and passwd from Optware on this NAS.
This thread suggests rebooting the Synology, and I tried that in desperation, but I get the same error after it finishes starting.