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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

                                                                                      KERBEROS(1)