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 remote hosts and without having to bother with
.rhosts files. Note that these utilities will work without passwords
only if the remote machines you deal with support the Kerberos system.
If you enter your username and kinit responds with this message:
kinit(v5): Client not found in Kerberos database while getting initial
you haven’t been registered as a Kerberos user. See your system
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, however, 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 don’t have to worry about their management.
Note, however, that tickets expire. Privileged tickets, such as those
with the instance ‘‘root’’, expire in a few minutes, while tickets that
carry more ordinary privileges may be good for several hours or a day,
depending on the installation’s policy. If your login session extends
beyond the time limit, you will have to re-authenticate yourself to
Kerberos to get new tickets. Use the kinit command to re-authenticate
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 kinit. 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, krdist (a Kerberized version
of rdist), ksu (a Kerberized version of su), login, and Xdm.
kdestroy(1), kinit(1), klist(1), kpasswd(1), rsh (1), rcp(1),
rlogin(1), telnet(1), ftp(1), krdist(1), ksu(1), sclient(1), xdm(1),
des_crypt(3), hash(3), krb5strings(3), krb5.conf(5), kdc.conf(5),
kadmin(8), kadmind(8), kdb5_util(8), telnetd(8), ftpd(8), rdistd(8),
sserver(8), klogind(8c), kshd(8c), login(8c)
Steve Miller, MIT Project Athena/Digital Equipment Corporation
Clifford Neuman, MIT Project Athena
Kerberos was developed at MIT. OpenVision rewrote and donated the
administration server, which is used in the current version of Kerberos
Copyright 1985,1986,1989-1996,2002 Massachusetts Institute of