Unable to join Fedora 20 machine to Active Directory RODC with realmd
The reason why you are seeing this error is because you can't write to the RODC to create a password. AD creates a computer password when the object is created and a randomly generated one while joining a domain.
You have to rely on Kerberos which caches the server password and when you join to RODC it will not prompt you. First create a keytab file on the writable DC for the specific Linux server then move it there, preferable to /etc/krb5.keytab and set permission to 600.