NAME¶
kerberos - introduction to the Kerberos system
DESCRIPTION¶
The Kerberos system authenticates individual users in a network environment.
After authenticating yourself to Kerberos, you can use Kerberos-enabled
programs without having to present passwords.
If you enter your username and
kinit responds with this message:
kinit(v5): Client not found in Kerberos database while getting initial
credentials
you haven't been registered as a Kerberos user. See your system administrator.
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:
david
jennifer/admin
joeuser@BLEEP.COM
cbrown/root@FUBAR.ORG
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 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
kinit. Once you have forwardable
tickets, most Kerberos programs have a command line option to forward them to
the remote host.
ENVIRONMENT VARIABLES¶
Several environment variables affect the operation of Kerberos-enabled programs.
These include:
- KRB5CCNAME
- Specifies the location of the credential cache, in the form
TYPE:residual. If no type prefix is present, the FILE
type is assumed and residual is the pathname of the cache file. A
collection of multiple caches may be used by specifying the DIR
type and the pathname of a private directory (which must already exist).
The default cache file is /tmp/krb5cc_ uid where uid is the
decimal user ID of the user.
- KRB5_KTNAME
- Specifies the location of the keytab file, in the form
TYPE: residual. If no type is present, the FILE type
is assumed and residual is the pathname of the keytab file. The
default keytab file is /etc/krb5.keytab.
- KRB5_CONFIG
- Specifies the location of the Kerberos configuration file.
The default is /etc/krb5.conf.
- KRB5_KDC_PROFILE
- Specifies the location of the KDC configuration file, which
contains additional configuration directives for the Key Distribution
Center daemon and associated programs. The default is
/usr/local/var/krb5kdc/kdc.conf.
- KRB5RCACHETYPE
- Specifies the default type of replay cache to use for
servers. Valid types include "dfl" for the normal file type and
"none" for no replay cache. KRB5RCACHEDIR Specifies the
default directory for replay caches used by servers. The default is the
value of the TMPDIR environment variable, or /var/tmp if
TMPDIR is not set.
- KRB5_TRACE
- Specifies a filename to write trace log output to. Trace
logs can help illuminate decisions made internally by the Kerberos
libraries. The default is not to write trace log output anywhere.
Most environment variables are disabled for certain programs, such as login
system programs and setuid programs, which are designed to be secure when run
within an untrusted process environment.
SEE ALSO¶
kdestroy(1),
kinit(1),
klist(1),
kswitch(1),
kpasswd(1),
ksu(1),
krb5.conf(5),
kdc.conf(5),
kadmin(1),
kadmind(8),
kdb5_util(8),
krb5kdc(8)
BUGS¶
AUTHORS¶
Steve Miller, MIT Project Athena/Digital Equipment Corporation
Clifford Neuman, MIT Project Athena
Greg Hudson, MIT Kerberos Consortium
HISTORY¶
The MIT Kerberos 5 implementation was developed at MIT, with contributions from
many outside parties. It is currently maintained by the MIT Kerberos
Consortium.
RESTRICTIONS¶
Copyright 1985,1986,1989-1996,2002,2011 Massachusetts Institute of
Technology