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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)