kerberos(7) - phpMan

KERBEROS(7) MIT Kerberos KERBEROS(7)

NAME
kerberos - Overview of using Kerberos

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 or certificates to those programs.

If you receive the following response from kinit(1):

kinit: 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 ssh service running on the machine ABC (ssh/ABC@REALM),
which is different from the ssh service running on the machine XYZ (ssh/XYZ@REALM). The
third part of a Kerberos name is the realm. The realm corresponds to the Kerberos service
providing authentication for the principal. Realms are conventionally all-uppercase, and
often match the end of hostnames in the realm (for instance, host01.example.com might be
in realm EXAMPLE.COM).

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 AT BLEEP.COM
cbrown/root AT FUBAR.ORG

When you authenticate yourself with Kerberos you get an initial Kerberos ticket. (A Ker-
beros ticket is an encrypted protocol message that provides authentication.) Kerberos
uses this ticket for network utilities such as ssh. The ticket transactions are done
transparently, so you don't have to worry about their management.

Note, however, that tickets expire. Administrators may configure more privileged tickets,
such as those with service or instance of root or admin, to expire in a few minutes, while
tickets that carry more ordinary privileges may be good for several hours or a day. If
your login session extends beyond the time limit, you will have to re-authenticate your-
self to Kerberos to get new tickets using the kinit(1) command.

Some tickets are renewable beyond their initial lifetime. This means that kinit -R can
extend their lifetime without requiring you to re-authenticate.

If you wish to delete your local tickets, use the kdestroy(1) command.

Kerberos tickets can be forwarded. In order to forward tickets, you must request forward-
able tickets when you kinit. Once you have forwardable tickets, most Kerberos programs
have a command line option to forward them to the remote host. This can be useful for,
e.g., running kinit on your local machine and then sshing into another to do work. Note
that this should not be done on untrusted machines since they will then have your tickets.

ENVIRONMENT VARIABLES
Several environment variables affect the operation of Kerberos-enabled programs. These
include:

KRB5CCNAME
Default name for the credentials cache file, in the form TYPE:residual. The type
of the default cache may determine the availability of a cache collection. FILE is
not a collection type; KEYRING, DIR, and KCM are.

If not set, the value of default_ccache_name from configuration files (see
KRB5_CONFIG) will be used. If that is also not set, the default type is FILE, and
the residual is the path /tmp/krb5cc_*uid*, where uid is the decimal user ID of the
user.

KRB5_KTNAME
Specifies the location of the default 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. If unset, FILE:/etc/krb5.keytab will be used.

KRB5_CONFIG
Specifies the location of the Kerberos configuration file. The default is
/etc/krb5.conf. Multiple filenames can be specified, separated by a colon; all
files which are present will be read.

KRB5_KDC_PROFILE
Specifies the location of the KDC configuration file, which contains additional
configuration directives for the Key Distribution Center daemon and associated pro-
grams. The default is /var/kerberos/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. The default is dfl.

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. For example, env
KRB5_TRACE=/dev/stderr kinit would send tracing information for kinit(1) to
/dev/stderr. The default is not to write trace log output anywhere.

KRB5_CLIENT_KTNAME
Default client keytab file name. If unset, FILE:/var/ker-
beros/krb5/user/%{euid}/client.keytab will be used).

KPROP_PORT
kprop(8) port to use. Defaults to 754.

Most environment variables are disabled for certain programs, such as login system pro-
grams 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
Robbie Harwood, Red Hat, Inc.

HISTORY
The MIT Kerberos 5 implementation was developed at MIT, with contributions from many out-
side parties. It is currently maintained by the MIT Kerberos Consortium.

RESTRICTIONS
Copyright 1985, 1986, 1989-1996, 2002, 2011, 2018 Masachusetts Institute of Technology

AUTHOR
MIT

1.17 KERBEROS(7)

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