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KERBEROS(1)                                                        KERBEROS(1)



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  quali-
       fied  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
               joeuserATBLEEP.COM
               cbrown/rootATFUBAR.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 man-
       agement.

       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, depend-
       ing 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 tick-
       ets 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 mul-
              tiple 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  /var/ker-
              beros/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 inter-
              nally 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  pro-
       grams, 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), kad-
       mind(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



                                                                   KERBEROS(1)