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
              /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 /etc/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:/etc/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  /etc/gss/mech  and  files  with  a  .conf suffix within the directory
              /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

       1985-2022, MIT