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KERBEROS(7)                      MIT Kerberos                      KERBEROS(7)
NAME
       kerberos - Overview of using Kerberos
DESCRIPTION
       The  Kerberos  system authenticates individual users in a network envi-
       ronment.  After authenticating yourself to Kerberos, you can  use  Ker-
       beros-enabled  programs without having to present passwords or certifi-
       cates to those programs.
       If you receive the following response from kinit(1):
       kinit: Client not found in Kerberos database while getting initial cre-
       dentials
       you haven't been registered as a Kerberos user.  See your system admin-
       istrator.
       A Kerberos name usually contains three parts.  The first  is  the  pri-
       mary,  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 Ker-
       beros 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 AT BLEEP.COM
          cbrown/root AT FUBAR.ORG
       When you authenticate yourself with Kerberos you get  an  initial  Ker-
       beros ticket.  (A Kerberos ticket is an encrypted protocol message that
       provides authentication.)  Kerberos uses this ticket for network utili-
       ties  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  ordi-
       nary  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  for-
       wardable  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 con-
              tains additional configuration directives for the Key  Distribu-
              tion  Center  daemon  and  associated  programs.  The default is
              /var/kerberos/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:/var/ker-
              beros/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 configu-
              ration.  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 contribu-
       tions from many outside parties.  It is currently maintained by the MIT
       Kerberos Consortium.
RESTRICTIONS
       Copyright  1985,  1986, 1989-1996, 2002, 2011, 2018 Masachusetts Insti-
       tute of Technology
AUTHOR
       MIT
COPYRIGHT
       1985-2020, MIT
1.18.2                                                             KERBEROS(7)