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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@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 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 yourself 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 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. 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 /usr/local/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 programs. The default
is /usr/local/var/krb5kdc/kdc.conf.
KRB5RCACHENAME
(New in release 1.18) Specifies the location of the default
replay cache, in the form type:residual. The file2 type with a
pathname residual specifies a replay cache file in the version-2
format in the specified location. The none type (residual is
ignored) disables the replay cache. The dfl type (residual is
ignored) indicates the default, which uses a file2 replay cache
in a temporary directory. The default is dfl:.
KRB5RCACHETYPE
Specifies the type of the default replay cache, if
KRB5RCACHENAME is unspecified. No residual can be specified, so
none and dfl are the only useful types.
KRB5RCACHEDIR
Specifies the directory used by the dfl replay cache type. 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:/usr/local/var/krb5/user/%{euid}/client.keytab will be
used).
KPROP_PORT
kprop(8) port to use. Defaults to 754.
GSS_MECH_CONFIG
Specifies a filename containing GSSAPI mechanism module
configuration. The default is to read /usr/local/etc/gss/mech
and files with a .conf suffix within the directory
/usr/local/etc/gss/mech.d.
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
Robbie Harwood, Red Hat, Inc.
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, 2018 Masachusetts
Institute of Technology
AUTHOR
MIT
COPYRIGHT
1985-2023, MIT
1.21.2 KERBEROS(7)