Before installing the Kerberos server a properly configured DNS server is needed for your domain. Since the Kerberos Realm by convention matches the domain name, this section uses the example.com domain configured in the section called “Primary Master”.

Also, Kerberos is a time sensitive protocol. So if the local system time between a client machine and the server differs by more than five minutes (by default), the workstation will not be able to authenticate. To correct the problem all hosts should have their time synchronized using the Network Time Protocol (NTP). For details on setting up NTP see the section called “Time Synchronisation with NTP”.

The first step in installing a Kerberos Realm is to install the krb5-kdc and krb5-admin-server packages. From a terminal enter:

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

You will be asked at the end of the install to supply a name for the Kerberos and Admin servers, which may or may not be the same server, for the realm.

Next, create the new realm with the kdb5_newrealm utility:

sudo krb5_newrealm

The questions asked during installation are used to configure the /etc/krb5.conf file. If you need to adjust the Key Distribution Center (KDC) settings simply edit the file and restart the krb5-kdc daemon.

Your new Kerberos Realm is now ready to authenticate clients.

In order to authenticate to a Kerberos Realm, the krb5-user and libpam-krb5 packages are needed, along with a few others that are not strictly necessary but make life easier. To install the packages enter the following in a terminal prompt:

sudo apt-get install krb5-user libpam-krb5 libpam-ccreds auth-client-config

The auth-client-config package allows simple configuration of PAM for authentication from multiple sources, and the libpam-ccreds will cache authentication credentials allowing you to login in case the Key Distribution Center (KDC) is unavailable. This package is also useful for laptops that may authenticate using Kerberos while on the corporate network, but will need to be accessed off the network as well.

To configure the client in a terminal enter:

sudo dpkg-reconfigure krb5-config

You will then be prompted to enter the name of the Kerberos Realm. Also, if you don't have DNS configured with Kerberos SRV records, the menu will prompt you for the hostname of the Key Distribution Center (KDC) and Realm Administration server.

The dpkg-reconfigure adds entries to the /etc/krb5.conf file for your Realm. You should have entries similar to the following:

[libdefaults]
        default_realm = EXAMPLE.COM
...
[realms]
        EXAMPLE.COM = }                
                kdc = 192.168.0.1               
                admin_server = 192.168.0.1
        }

You can test the configuration by requesting a ticket using the kinit utility. For example:

kinit [email protected]
Password for [email protected]:

When a ticket has been granted, the details can be viewed using klist:

klist
Ticket cache: FILE:/tmp/krb5cc_1000
Default principal: [email protected]

Valid starting     Expires            Service principal
07/24/08 05:18:56  07/24/08 15:18:56  krbtgt/[email protected]
        renew until 07/25/08 05:18:57


Kerberos 4 ticket cache: /tmp/tkt1000
klist: You have no tickets cached

Next, use the auth-client-config to configure the libpam-krb5 module to request a ticket during login:

sudo auth-client-config -a -p kerberos_example

You will should now receive a ticket upon successful login authentication.