[Samba] kerberos

[Saad Benateigha]

I am having a problem using kerberos 

I have installed samba4, and it appears to work correctly 
However I want to create a service principle 
and every time I try to use 
kadmin -p admin 
I get this error: 
Database error! Required KADM5 principal missing while initializing kadmin interface 

What am I doing wrong? 
Is there another command since Samba4 has it own kerberos? 
Please shed some light on my dilemma. 

Thank you 
Saad