The login should be admin/root@REALM or admin/admin@REALM and the password you used when creating the KDC database.
The exact value should be in your
an example above form my centOS the location could be different in Ubuntu
So with the above value my login would be either
admin/admin@TEST.COM or root/admin@TEST.COM or whatever you chose in the begining
The password you entered during the creation of the database see below extract is the one you use in the above scenario
# kdb5_util create -s
Loading random data
Initializing database '/var/kerberos/krb5kdc/principal' for realm 'TEST.COM',
master key name 'K/M@TEST.COM'
You will be prompted for the database Master Password.
It is important that you NOT FORGET this password.
Enter KDC database master key:
Re-enter KDC database master key to verify:
Or whatever you chose I hope you keep the password safely !!