KERBEROS(1)KERBEROS(1)NAMEkerberos - introduction to the Kerberos system
DESCRIPTION
The Kerberos system authenticates individual users in a network envi‐
ronment. After authenticating yourself to Kerberos, you can use Ker‐
beros-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 admin‐
istrator.
A Kerberos name usually contains three parts. The first is the pri‐
mary, 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 Ker‐
beros ticket. (A Kerberos ticket is an encrypted protocol message that
provides authentication.) Kerberos uses this ticket for network utili‐
ties such as rlogin and rcp. The ticket transactions are done trans‐
parently, 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 ses‐
sion. 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 for‐
wardable 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 col‐
lection 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 con‐
tains additional configuration directives for the Key Distribu‐
tion Center daemon and associated programs. 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. KRB5RCACHEDIR Specifies the default direc‐
tory 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 any‐
where.
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 ALSOkdestroy(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)BUGSAUTHORS
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 contribu‐
tions 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
KERBEROS(1)
