apt - Unable to locate krb5-admin-server krb5-kdc

I am trying to install Kerberos5 on my ubuntu-14.10-server-64bit, then I type the command:

sudo apt-get install krb5-admin-server krb5-kdc

I receive

E: Unable to locate package krb5-admin-server
E: Unable to locate package krb5-kdc

What can be the problem?
Thanks

I post this as an answer because it solved the problem.

Do a sudo apt-get update to update the repos cache before sudo apt-get install