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

1.20.1                                                                                               KERBEROS(7)