kerberos - Introduction to the Kerberos system
The Kerberos system authenticates individual users in a network
environment. After authenticating yourself to Kerberos, you can use
network utilities such as rlogin, rcp, and rsh without having to
present passwords to the remote hosts and without having to edit and
use .rhosts files. Note that these utilities will work without
passwords only if the remote machines you deal with support the
If you enter your username and the remote machine is not a Kerberos
system, you will get the following message:
Principal unknown (Kerberos) you haven't been registered as a
You will have to see your system administrator when the above message
A Kerberos name usually contains three parts. The first is the
primary, which is usually a user's or service's name. The second is
the instance, which in the case of a user is usually null. Some users
may have privileged instances, such as ``root'' or ``admin''. In the
case of a service, the instance is the fully qualified name of the
machine on which it runs; i.e. there can be an rlogin service running
on the machine ABC, which is different from the rlogin service running
on the machine XYZ. The third part of a Kerberos name is the realm.
The realm corresponds to the Kerberos service providing authentication
for the principal.
When writing a Kerberos name, the principal name is separated from the
instance (if not null) by a slash (/), and the realm (if not the local
realm) follows, preceded by an ``@'' sign. The following are examples
of valid Kerberos names:
When you authenticate yourself with Kerberos, you get an initial
Kerberos ticket. A Kerberos ticket is an encrypted protocol message
that provides authentication. Kerberos uses this ticket for network
utilities such as rlogin and rcp. The ticket transactions are done
transparently, so you do not have to worry about their management.
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Note, however, that tickets will expire. Privileged tickets, such as
those with the instance ``root'', expire with in a few minutes, while
tickets that carry more ordinary privileges may be valid for several
hours or a day, depending on the Kerberos server configuration. If
your login session extends beyond the lifetime limit, you will have to
re-authenticate yourself to Kerberos to get new tickets. Use the kinit
command to re-authenticate yourself.
If you use the kinit command to get your tickets, make sure you use
the kdestroy command to destroy your tickets before you end your login
session. You should put the kdestroy command in your .logout file so
that your tickets will be destroyed automatically when you logout. For
more information about the kinit and kdestroy commands, see the
kinit(1) and kdestroy(1) manual pages.
Kerberos tickets can be forwarded. In order to forward tickets, you
must request forwardable tickets when you use the kinit command. Once
you have forwardable tickets, most Kerberos programs have a command
line option to forward them to the remote host.
Currently, Kerberos support is available for the following network
services: rlogin, rsh, rcp, telnet, ftp, and login.
Kerberos was developed by the Massachusetts Institute of Technology by
Steve Miller, MIT Project Athena/Digital Equipment Corporation, and
Clifford Neuman, MIT Project Athena.
kdestroy(1), kinit(1), klist(1), kpasswd(1), krb5.conf(4), libkrb5(3).
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