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krb5.conf(5)                     MIT Kerberos                     krb5.conf(5)




NAME

       krb5.conf - Kerberos configuration file

       The krb5.conf file contains Kerberos configuration information, includ-
       ing the locations of KDCs and admin servers for the Kerberos realms  of
       interest, defaults for the current realm and for Kerberos applications,
       and mappings of hostnames onto Kerberos realms.  Normally,  you  should
       install  your  krb5.conf  file in the directory /etc.  You can override
       the default location by setting the environment  variable  KRB5_CONFIG.
       Multiple colon-separated filenames may be specified in KRB5_CONFIG; all
       files which are present will be read.  Starting in release 1.14, direc-
       tory  names  can also be specified in KRB5_CONFIG; all files within the
       directory  whose  names  consist  solely  of  alphanumeric  characters,
       dashes, or underscores will be read.


STRUCTURE

       The krb5.conf file is set up in the style of a Windows INI file.  Lines
       beginning with '#' or  ';'  (possibly  after  initial  whitespace)  are
       ignored  as  comments.   Sections  are  headed  by the section name, in
       square brackets.  Each section may contain zero or more  relations,  of
       the form:

          foo = bar

       or:

          fubar = {
              foo = bar
              baz = quux
          }

       Placing  a  '*'  after  the closing bracket of a section name indicates
       that the section is final, meaning that if  the  same  section  appears
       within  a  later  file specified in KRB5_CONFIG, it will be ignored.  A
       subsection can be marked as final by placing a '*' after either the tag
       name or the closing brace.

       The  krb5.conf file can include other files using either of the follow-
       ing directives at the beginning of a line:

          include FILENAME
          includedir DIRNAME

       FILENAME or DIRNAME should be an  absolute  path.  The  named  file  or
       directory  must  exist and be readable.  Including a directory includes
       all files within the directory whose names consist solely  of  alphanu-
       meric  characters,  dashes,  or underscores.  Starting in release 1.15,
       files with names ending in ".conf" are also included, unless  the  name
       begins  with ".".  Included profile files are syntactically independent
       of their parents, so each included  file  must  begin  with  a  section
       header.   Starting  in  release  1.17,  files  are read in alphanumeric
       order; in previous releases, they may be read in any order.

       The krb5.conf file can specify that configuration  should  be  obtained
       from  a loadable module, rather than the file itself, using the follow-
       ing directive at the beginning of a line before any section headers:

          module MODULEPATH:RESIDUAL

       MODULEPATH may be relative to the library path of  the  krb5  installa-
       tion,  or it may be an absolute path.  RESIDUAL is provided to the mod-
       ule at initialization time.  If  krb5.conf  uses  a  module  directive,
       kdc.conf(5) should also use one if it exists.


SECTIONS

       The krb5.conf file may contain the following sections:

                    +---------------+----------------------------+
                    |[libdefaults]  | Settings  used by the Ker- |
                    |               | beros V5 library           |
                    +---------------+----------------------------+
                    |[realms]       | Realm-specific     contact |
                    |               | information and settings   |
                    +---------------+----------------------------+
                    |[domain_realm] | Maps  server  hostnames to |
                    |               | Kerberos realms            |
                    +---------------+----------------------------+
                    |[capaths]      | Authentication  paths  for |
                    |               | non-hierarchical           |
                    |               | cross-realm                |
                    +---------------+----------------------------+
                    |[appdefaults]  | Settings used by some Ker- |
                    |               | beros V5 applications      |
                    +---------------+----------------------------+
                    |[plugins]      | Controls   plugin   module |
                    |               | registration               |
                    +---------------+----------------------------+

       Additionally, krb5.conf may include any of the relations  described  in
       kdc.conf(5), but it is not a recommended practice.

   [libdefaults]
       The libdefaults section may contain any of the following relations:

       allow_weak_crypto
              If  this  flag  is  set to false, then weak encryption types (as
              noted in Encryption_types in kdc.conf(5)) will be  filtered  out
              of  the  lists  default_tgs_enctypes,  default_tkt_enctypes, and
              permitted_enctypes.  The default value for this tag is false.

       canonicalize
              If this flag is set to true, initial ticket requests to the  KDC
              will  request canonicalization of the client principal name, and
              answers with different  client  principals  than  the  requested
              principal will be accepted.  The default value is false.

       ccache_type
              This  parameter  determines the format of credential cache types
              created by kinit(1) or other programs.  The default value is  4,
              which represents the most current format.  Smaller values can be
              used for compatibility with very old implementations of Kerberos
              which interact with credential caches on the same host.

       clockskew
              Sets  the  maximum allowable amount of clockskew in seconds that
              the library will tolerate before assuming that a  Kerberos  mes-
              sage is invalid.  The default value is 300 seconds, or five min-
              utes.

              The clockskew setting is also used when evaluating ticket  start
              and  expiration  times.   For example, tickets that have reached
              their expiration time can still be used (and renewed if they are
              renewable tickets) if they have been expired for a shorter dura-
              tion than the clockskew setting.

       default_ccache_name
              This relation specifies  the  name  of  the  default  credential
              cache.  The default is KCM:.  This relation is subject to param-
              eter expansion (see below).  New in release 1.11.

       default_client_keytab_name
              This relation specifies the  name  of  the  default  keytab  for
              obtaining     client     credentials.      The     default    is
              FILE:/opt/local/var/krb5/user/%{euid}/client.keytab.  This rela-
              tion  is  subject  to  parameter  expansion (see below).  New in
              release 1.11.

       default_keytab_name
              This relation specifies the default keytab name to  be  used  by
              application    servers   such   as   sshd.    The   default   is
              FILE:/etc/krb5.keytab.  This relation is  subject  to  parameter
              expansion (see below).

       default_rcache_name
              This  relation  specifies  the name of the default replay cache.
              The default is dfl:.  This  relation  is  subject  to  parameter
              expansion (see below).  New in release 1.18.

       default_realm
              Identifies  the  default Kerberos realm for the client.  Set its
              value to your Kerberos realm.  If this value is not set, then  a
              realm  must  be  specified  with  every  Kerberos principal when
              invoking programs such as kinit(1).

       default_tgs_enctypes
              Identifies the supported list of session  key  encryption  types
              that  the  client should request when making a TGS-REQ, in order
              of preference from highest to lowest.  The list may be delimited
              with  commas or whitespace.  See Encryption_types in kdc.conf(5)
              for a list of the accepted values for  this  tag.   Starting  in
              release  1.18,  the default value is the value of permitted_enc-
              types.  For previous releases or if  permitted_enctypes  is  not
              set,    the    default    value    is    aes256-cts-hmac-sha1-96
              aes128-cts-hmac-sha1-96               aes256-cts-hmac-sha384-192
              aes128-cts-hmac-sha256-128 des3-cbc-sha1 arcfour-hmac-md5 camel-
              lia256-cts-cmac camellia128-cts-cmac.

              Do not set this unless required for specific  backward  compati-
              bility  purposes;  stale  values  of  this  setting  can prevent
              clients from taking advantage of new stronger enctypes when  the
              libraries are upgraded.

       default_tkt_enctypes
              Identifies  the  supported  list of session key encryption types
              that the client should request when making an AS-REQ,  in  order
              of preference from highest to lowest.  The format is the same as
              for default_tgs_enctypes.  Starting in release 1.18, the default
              value is the value of permitted_enctypes.  For previous releases
              or if permitted_enctypes  is  not  set,  the  default  value  is
              aes256-cts-hmac-sha1-96                  aes128-cts-hmac-sha1-96
              aes256-cts-hmac-sha384-192            aes128-cts-hmac-sha256-128
              des3-cbc-sha1   arcfour-hmac-md5   camellia256-cts-cmac   camel-
              lia128-cts-cmac.

              Do not set this unless required for specific  backward  compati-
              bility  purposes;  stale  values  of  this  setting  can prevent
              clients from taking advantage of new stronger enctypes when  the
              libraries are upgraded.

       dns_canonicalize_hostname
              Indicate whether name lookups will be used to canonicalize host-
              names for use in service principal names.  Setting this flag  to
              false  can  improve  security  by  reducing reliance on DNS, but
              means  that  short  hostnames  will  not  be  canonicalized   to
              fully-qualified  hostnames.   If  this option is set to fallback
              (new in release 1.18), DNS canonicalization will  only  be  per-
              formed  the  server hostname is not found with the original name
              when requesting credentials.  The default value is true.

       dns_lookup_kdc
              Indicate whether DNS SRV records should be used  to  locate  the
              KDCs  and  other  servers for a realm, if they are not listed in
              the  krb5.conf  information  for  the  realm.   (Note  that  the
              admin_server entry must be in the krb5.conf realm information in
              order to contact kadmind, because  the  DNS  implementation  for
              kadmin is incomplete.)

              Enabling  this  option  does open up a type of denial-of-service
              attack, if someone spoofs the DNS records and redirects  you  to
              another  server.   However,  it's no worse than a denial of ser-
              vice, because that fake KDC will be unable  to  decode  anything
              you  send  it  (besides the initial ticket request, which has no
              encrypted data), and anything the fake KDC  sends  will  not  be
              trusted  without  verification  using  some secret that it won't
              know.

       dns_uri_lookup
              Indicate whether DNS URI records should be used  to  locate  the
              KDCs  and  other  servers for a realm, if they are not listed in
              the krb5.conf information for the realm.  SRV records  are  used
              as  a  fallback if no URI records were found.  The default value
              is true.  New in release 1.15.

       enforce_ok_as_delegate
              If this flag to true, GSSAPI credential delegation will be  dis-
              abled  when  the  ok-as-delegate  flag is not set in the service
              ticket.  If this flag is false, the ok-as-delegate  ticket  flag
              is  only  enforced  when  an  application  specifically requests
              enforcement.  The default value is false.

       err_fmt
              This relation allows for custom error message formatting.  If  a
              value is set, error messages will be formatted by substituting a
              normal error message for %M and an error  code  for  %C  in  the
              value.

       extra_addresses
              This allows a computer to use multiple local addresses, in order
              to allow Kerberos to work in a  network  that  uses  NATs  while
              still using address-restricted tickets.  The addresses should be
              in a comma-separated list.  This option has no effect  if  noad-
              dresses is true.

       forwardable
              If  this  flag  is  true, initial tickets will be forwardable by
              default, if allowed by the KDC.  The default value is false.

       ignore_acceptor_hostname
              When accepting GSSAPI or krb5 security contexts  for  host-based
              service  principals,  ignore  any hostname passed by the calling
              application, and allow clients to authenticate  to  any  service
              principal in the keytab matching the service name and realm name
              (if given).  This option can improve the  administrative  flexi-
              bility  of  server  applications  on multihomed hosts, but could
              compromise the security of virtual  hosting  environments.   The
              default value is false.  New in release 1.10.

       k5login_authoritative
              If  this  flag  is  true,  principals  must be listed in a local
              user's k5login file to be granted login access, if a .k5login(5)
              file  exists.   If  this flag is false, a principal may still be
              granted login access through other mechanisms even if a  k5login
              file  exists but does not list the principal.  The default value
              is true.

       k5login_directory
              If set, the library will look for a local  user's  k5login  file
              within the named directory, with a filename corresponding to the
              local username.  If not set, the library will look  for  k5login
              files  in the user's home directory, with the filename .k5login.
              For security reasons, .k5login files must be owned by the  local
              user or by root.

       kcm_mach_service
              On macOS only, determines the name of the bootstrap service used
              to contact the KCM daemon for the KCM credential cache type.  If
              the  value  is  -,  Mach RPC will not be used to contact the KCM
              daemon.  The default value is org.h5l.kcm.

       kcm_socket
              Determines the path to the Unix domain socket used to access the
              KCM  daemon  for the KCM credential cache type.  If the value is
              -, Unix domain sockets will not be used to contact the KCM  dae-
              mon.  The default value is /var/run/.heim_org.h5l.kcm-socket.

       kdc_default_options
              Default  KDC options (Xored for multiple values) when requesting
              initial  tickets.   By  default  it   is   set   to   0x00000010
              (KDC_OPT_RENEWABLE_OK).

       kdc_timesync
              Accepted values for this relation are 1 or 0.  If it is nonzero,
              client machines will compute the difference between  their  time
              and  the time returned by the KDC in the timestamps in the tick-
              ets and use this value to correct for an inaccurate system clock
              when  requesting  service tickets or authenticating to services.
              This corrective factor is only used by the Kerberos library;  it
              is not used to change the system clock.  The default value is 1.

       noaddresses
              If this flag is true, requests for initial tickets will  not  be
              made  with  address restrictions set, allowing the tickets to be
              used across NATs.  The default value is true.

       permitted_enctypes
              Identifies the encryption types that  servers  will  permit  for
              session  keys  and  for  ticket  and  authenticator  encryption,
              ordered by preference  from  highest  to  lowest.   Starting  in
              release  1.18,  this  tag  also  acts  as  the default value for
              default_tgs_enctypes  and  default_tkt_enctypes.   The   default
              value     for     this     tag     is    aes256-cts-hmac-sha1-96
              aes128-cts-hmac-sha1-96               aes256-cts-hmac-sha384-192
              aes128-cts-hmac-sha256-128 des3-cbc-sha1 arcfour-hmac-md5 camel-
              lia256-cts-cmac camellia128-cts-cmac.

       plugin_base_dir
              If set, determines the base directory  where  krb5  plugins  are
              located.   The default value is the krb5/plugins subdirectory of
              the krb5 library directory.  This relation is subject to parame-
              ter expansion (see below) in release 1.17 and later.

       preferred_preauth_types
              This  allows  you  to  set the preferred preauthentication types
              which the client will attempt before others which may be  adver-
              tised  by a KDC.  The default value for this setting is "17, 16,
              15, 14", which forces libkrb5 to attempt to use PKINIT if it  is
              supported.

       proxiable
              If  this  flag  is  true,  initial  tickets will be proxiable by
              default, if allowed by the KDC.  The default value is false.

       qualify_shortname
              If this string is set, it determines the domain suffix for  sin-
              gle-component  hostnames  when  DNS canonicalization is not used
              (either because dns_canonicalize_hostname is  false  or  because
              forward  canonicalization  failed).   The  default  value is the
              first search domain of the system's DNS configuration.  To  dis-
              able qualification of shortnames, set this relation to the empty
              string with qualify_shortname = "".  (New in release 1.18.)

       rdns   If this flag is true, reverse name lookup will be used in  addi-
              tion  to forward name lookup to canonicalizing hostnames for use
              in service principal names.  If dns_canonicalize_hostname is set
              to false, this flag has no effect.  The default value is true.

       realm_try_domains
              Indicate  whether  a  host's domain components should be used to
              determine the Kerberos realm of the host.   The  value  of  this
              variable  is  an integer: -1 means not to search, 0 means to try
              the host's domain itself, 1 means to also try the domain's imme-
              diate  parent,  and so forth.  The library's usual mechanism for
              locating Kerberos realms is used to determine whether  a  domain
              is   a   valid  realm,  which  may  involve  consulting  DNS  if
              dns_lookup_kdc is set.  The default is not to search domain com-
              ponents.

       renew_lifetime
              (duration string.)  Sets the default renewable lifetime for ini-
              tial ticket requests.  The default value is 0.

       spake_preauth_groups
              A whitespace or comma-separated list of  words  which  specifies
              the  groups  allowed  for SPAKE preauthentication.  The possible
              values are:

                        +-------------+----------------------------+
                        |edwards25519 | Edwards25519  curve   (RFC |
                        |             | 7748)                      |
                        +-------------+----------------------------+
                        |P-256        | NIST   P-256   curve  (RFC |
                        |             | 5480)                      |
                        +-------------+----------------------------+
                        |P-384        | NIST  P-384   curve   (RFC |
                        |             | 5480)                      |
                        +-------------+----------------------------+
                        |P-521        | NIST   P-521   curve  (RFC |
                        |             | 5480)                      |
                        +-------------+----------------------------+

              The default value for the client is edwards25519.   The  default
              value for the KDC is empty.  New in release 1.17.

       ticket_lifetime
              (duration string.)  Sets the default lifetime for initial ticket
              requests.  The default value is 1 day.

       udp_preference_limit
              When sending a message to the KDC, the library  will  try  using
              TCP  before  UDP if the size of the message is above udp_prefer-
              ence_limit.   If  the  message  is  smaller   than   udp_prefer-
              ence_limit,  then  UDP  will be tried before TCP.  Regardless of
              the size, both protocols will be  tried  if  the  first  attempt
              fails.

       verify_ap_req_nofail
              If  this flag is true, then an attempt to verify initial creden-
              tials will fail if the client machine does not  have  a  keytab.
              The default value is false.

       client_aware_channel_bindings
              If  this flag is true, then all application protocol authentica-
              tion requests will be flagged to indicate that  the  application
              supports  channel bindings when operating over a secure channel.
              The default value is false.

   [realms]
       Each tag in the [realms] section of the file is the name of a  Kerberos
       realm.  The value of the tag is a subsection with relations that define
       the properties of that particular realm.  For each realm, the following
       tags may be specified in the realm's subsection:

       admin_server
              Identifies  the host where the administration server is running.
              Typically, this is the primary Kerberos server.  This  tag  must
              be  given  a  value  in order to communicate with the kadmind(8)
              server for the realm.

       auth_to_local
              This tag allows you to set a general rule for mapping  principal
              names  to  local user names.  It will be used if there is not an
              explicit mapping for the principal name  that  is  being  trans-
              lated. The possible values are:

              RULE:exp
                     The local name will be formulated from exp.

                     The    format   for   exp   is   [n:string](regexp)s/pat-
                     tern/replacement/g.  The integer  n  indicates  how  many
                     components  the  target  principal  should have.  If this
                     matches, then a string will be formed from  string,  sub-
                     stituting  the realm of the principal for $0 and the n'th
                     component of the principal for $n (e.g., if the principal
                     was  johndoe/admin  then  [2:$2$1foo] would result in the
                     string adminjohndoefoo).  If this string matches  regexp,
                     then the s//[g] substitution command will be run over the
                     string.  The optional g will cause the substitution to be
                     global  over  the  string,  instead of replacing only the
                     first match in the string.

              DEFAULT
                     The principal name will be used as the local  user  name.
                     If the principal has more than one component or is not in
                     the default realm, this rule is not  applicable  and  the
                     conversion will fail.

              For example:

                 [realms]
                     ATHENA.MIT.EDU = {
                         auth_to_local = RULE:[2:$1](johndoe)s/^.*$/guest/
                         auth_to_local = RULE:[2:$1;$2](^.*;admin$)s/;admin$//
                         auth_to_local = RULE:[2:$2](^.*;root)s/^.*$/root/
                         auth_to_local = DEFAULT
                     }

              would  result in any principal without root or admin as the sec-
              ond component to be translated with the default rule.  A princi-
              pal  with a second component of admin will become its first com-
              ponent.  root will be used as the local name for  any  principal
              with  a  second  component  of root.  The exception to these two
              rules are any principals johndoe/*, which will  always  get  the
              local name guest.

       auth_to_local_names
              This subsection allows you to set explicit mappings from princi-
              pal names to local user names.  The tag is the mapping name, and
              the value is the corresponding local user name.

       default_domain
              This  tag  specifies  the  domain  used to expand hostnames when
              translating Kerberos 4 service principals to Kerberos 5  princi-
              pals  (for  example, when converting rcmd.hostname to host/host-
              name.domain).

       disable_encrypted_timestamp
              If this flag is true, the  client  will  not  perform  encrypted
              timestamp  preauthentication  if  requested by the KDC.  Setting
              this flag can help  to  prevent  dictionary  attacks  by  active
              attackers,  if  the realm's KDCs support SPAKE preauthentication
              or if initial authentication always uses  another  mechanism  or
              always  uses  FAST.   This flag persists across client referrals
              during initial authentication.  This flag does not  prevent  the
              KDC from offering encrypted timestamp.  New in release 1.17.

       http_anchors
              When  KDCs  and kpasswd servers are accessed through HTTPS prox-
              ies, this tag can be used to specify the location of the CA cer-
              tificate  which should be trusted to issue the certificate for a
              proxy server.  If left unspecified, the system-wide default  set
              of CA certificates is used.

              The  syntax  for  values  is  similar  to that of values for the
              pkinit_anchors tag:

              FILE: filename

              filename is assumed to be the name of an OpenSSL-style ca-bundle
              file.

              DIR: dirname

              dirname is assumed to be an directory which contains CA certifi-
              cates.  All files in the directory will  be  examined;  if  they
              contain certificates (in PEM format), they will be used.

              ENV: envvar

              envvar  specifies  the name of an environment variable which has
              been set to a value conforming to one of  the  previous  values.
              For   example,  ENV:X509_PROXY_CA,  where  environment  variable
              X509_PROXY_CA has been set to FILE:/tmp/my_proxy.pem.

       kdc    The name or address of a host running a KDC for that realm.   An
              optional  port  number,  separated from the hostname by a colon,
              may be included.  If the name or address  contains  colons  (for
              example,  if it is an IPv6 address), enclose it in square brack-
              ets to distinguish the colon from a port  separator.   For  your
              computer  to be able to communicate with the KDC for each realm,
              this tag must be given a value in each realm subsection  in  the
              configuration  file, or there must be DNS SRV records specifying
              the KDCs.

       kpasswd_server
              Points to the server where all the  password  changes  are  per-
              formed.   If there is no such entry, DNS will be queried (unless
              forbidden  by  dns_lookup_kdc).   Finally,  port  464   on   the
              admin_server host will be tried.

       master_kdc
              The  name  for  primary_kdc prior to release 1.19.  Its value is
              used as a fallback if primary_kdc is not specified.

       primary_kdc
              Identifies the primary KDC(s).  Currently, this tag is  used  in
              only one case: If an attempt to get credentials fails because of
              an invalid password, the client software will attempt to contact
              the  primary  KDC,  in  case  the  user's password has just been
              changed, and the updated database has not been propagated to the
              replica servers yet.  New in release 1.19.

       v4_instance_convert
              This subsection allows the administrator to configure exceptions
              to the default_domain mapping rule.  It  contains  V4  instances
              (the tag name) which should be translated to some specific host-
              name (the tag value) as the second component in  a  Kerberos  V5
              principal name.

       v4_realm
              This  relation  is used by the krb524 library routines when con-
              verting a V5 principal name to a V4 principal name.  It is  used
              when  the  V4 realm name and the V5 realm name are not the same,
              but still share the same principal names and passwords. The  tag
              value is the Kerberos V4 realm name.

   [domain_realm]
       The [domain_realm] section provides a translation from a domain name or
       hostname to a Kerberos realm name.  The tag name can be a host name  or
       domain  name,  where domain names are indicated by a prefix of a period
       (.).  The value of the relation is the Kerberos  realm  name  for  that
       particular  host  or  domain.  A host name relation implicitly provides
       the corresponding domain name relation, unless an explicit domain  name
       relation  is  provided.  The Kerberos realm may be identified either in
       the realms section or using DNS SRV records.   Host  names  and  domain
       names should be in lower case.  For example:

          [domain_realm]
              crash.mit.edu = TEST.ATHENA.MIT.EDU
              .dev.mit.edu = TEST.ATHENA.MIT.EDU
              mit.edu = ATHENA.MIT.EDU

       maps  the host with the name crash.mit.edu into the TEST.ATHENA.MIT.EDU
       realm.  The second entry maps all hosts under  the  domain  dev.mit.edu
       into  the  TEST.ATHENA.MIT.EDU  realm,  but  not the host with the name
       dev.mit.edu.  That host is matched by the third entry, which  maps  the
       host mit.edu and all hosts under the domain mit.edu that do not match a
       preceding rule into the realm ATHENA.MIT.EDU.

       If no translation entry applies to a hostname used for a service  prin-
       cipal  for  a  service  ticket  request,  the library will try to get a
       referral to the appropriate realm from the client realm's KDC.  If that
       does  not  succeed, the host's realm is considered to be the hostname's
       domain portion converted to  uppercase,  unless  the  realm_try_domains
       setting in [libdefaults] causes a different parent domain to be used.

   [capaths]
       In  order  to perform direct (non-hierarchical) cross-realm authentica-
       tion, configuration is needed to  determine  the  authentication  paths
       between realms.

       A  client will use this section to find the authentication path between
       its realm and the realm of the server.  The server will use  this  sec-
       tion  to verify the authentication path used by the client, by checking
       the transited field of the received ticket.

       There is a tag for each participating client realm, and  each  tag  has
       subtags  for each of the server realms.  The value of the subtags is an
       intermediate realm which may participate in the cross-realm authentica-
       tion.  The subtags may be repeated if there is more then one intermedi-
       ate realm.  A value of  "."  means  that  the  two  realms  share  keys
       directly,  and no intermediate realms should be allowed to participate.

       Only those entries which will be needed on the  client  or  the  server
       need to be present.  A client needs a tag for its local realm with sub-
       tags for all the realms of servers it will need to authenticate to.   A
       server  needs a tag for each realm of the clients it will serve, with a
       subtag of the server realm.

       For example, ANL.GOV, PNL.GOV, and NERSC.GOV all wish to use the ES.NET
       realm  as  an  intermediate realm.  ANL has a sub realm of TEST.ANL.GOV
       which will authenticate with NERSC.GOV but not PNL.GOV.  The  [capaths]
       section for ANL.GOV systems would look like this:

          [capaths]
              ANL.GOV = {
                  TEST.ANL.GOV = .
                  PNL.GOV = ES.NET
                  NERSC.GOV = ES.NET
                  ES.NET = .
              }
              TEST.ANL.GOV = {
                  ANL.GOV = .
              }
              PNL.GOV = {
                  ANL.GOV = ES.NET
              }
              NERSC.GOV = {
                  ANL.GOV = ES.NET
              }
              ES.NET = {
                  ANL.GOV = .
              }

       The  [capaths] section of the configuration file used on NERSC.GOV sys-
       tems would look like this:

          [capaths]
              NERSC.GOV = {
                  ANL.GOV = ES.NET
                  TEST.ANL.GOV = ES.NET
                  TEST.ANL.GOV = ANL.GOV
                  PNL.GOV = ES.NET
                  ES.NET = .
              }
              ANL.GOV = {
                  NERSC.GOV = ES.NET
              }
              PNL.GOV = {
                  NERSC.GOV = ES.NET
              }
              ES.NET = {
                  NERSC.GOV = .
              }
              TEST.ANL.GOV = {
                  NERSC.GOV = ANL.GOV
                  NERSC.GOV = ES.NET
              }

       When a subtag is used more than once within a tag, clients will use the
       order  of  values  to  determine  the path.  The order of values is not
       important to servers.

   [appdefaults]
       Each tag in the [appdefaults] section names a Kerberos  V5  application
       or  an  option  that  is  used by some Kerberos V5 application[s].  The
       value of the tag defines the default behaviors for that application.

       For example:

          [appdefaults]
              telnet = {
                  ATHENA.MIT.EDU = {
                      option1 = false
                  }
              }
              telnet = {
                  option1 = true
                  option2 = true
              }
              ATHENA.MIT.EDU = {
                  option2 = false
              }
              option2 = true

       The above four ways of specifying the value of an option are  shown  in
       order  of  decreasing precedence. In this example, if telnet is running
       in the realm EXAMPLE.COM, it  should,  by  default,  have  option1  and
       option2   set  to  true.   However,  a  telnet  program  in  the  realm
       ATHENA.MIT.EDU should have option1 set to  false  and  option2  set  to
       true.   Any other programs in ATHENA.MIT.EDU should have option2 set to
       false by default.  Any programs running in  other  realms  should  have
       option2 set to true.

       The  list  of  specifiable options for each application may be found in
       that application's man pages.  The application defaults specified  here
       are overridden by those specified in the realms section.

   [plugins]
          o pwqual interface

          o kadm5_hook interface

          o clpreauth and kdcpreauth interfaces

       Tags  in  the  [plugins] section can be used to register dynamic plugin
       modules and to turn modules on  and  off.   Not  every  krb5  pluggable
       interface  uses  the [plugins] section; the ones that do are documented
       here.

       New in release 1.9.

       Each pluggable interface corresponds to a subsection of [plugins].  All
       subsections support the same tags:

       disable
              This  tag may have multiple values. If there are values for this
              tag, then the named modules will be disabled for  the  pluggable
              interface.

       enable_only
              This  tag may have multiple values. If there are values for this
              tag, then only the named modules will be enabled for  the  plug-
              gable interface.

       module This  tag  may  have multiple values.  Each value is a string of
              the form modulename:pathname, which  causes  the  shared  object
              located  at  pathname to be registered as a dynamic module named
              modulename for the pluggable interface.  If pathname is  not  an
              absolute  path,  it  will  be  treated  as relative to the plug-
              in_base_dir value from [libdefaults].

       For pluggable interfaces where module order matters, modules registered
       with  a  module  tag  normally come first, in the order they are regis-
       tered, followed by built-in modules in the order  they  are  documented
       below.   If  enable_only  tags  are  used, then the order of those tags
       overrides the normal module order.

       The following subsections are currently supported within the  [plugins]
       section:

   ccselect interface
       The ccselect subsection controls modules for credential cache selection
       within a cache collection.  In addition to any registered dynamic  mod-
       ules,  the  following  built-in modules exist (and may be disabled with
       the disable tag):

       k5identity
              Uses a .k5identity file in the user's home directory to select a
              client principal

       realm  Uses  the  service  realm to guess an appropriate cache from the
              collection

       hostname
              If the service principal is host-based, uses the  service  host-
              name to guess an appropriate cache from the collection

   pwqual interface
       The  pwqual subsection controls modules for the password quality inter-
       face, which is  used  to  reject  weak  passwords  when  passwords  are
       changed.  The following built-in modules exist for this interface:

       dict   Checks against the realm dictionary file

       empty  Rejects empty passwords

       hesiod Checks  against  user information stored in Hesiod (only if Ker-
              beros was built with Hesiod support)

       princ  Checks against components of the principal name

   kadm5_hook interface
       The kadm5_hook interface provides plugins with information on principal
       creation,  modification, password changes and deletion.  This interface
       can be used to write a plugin to synchronize MIT Kerberos with  another
       database  such  as  Active Directory.  No plugins are built in for this
       interface.

   kadm5_auth interface
       The kadm5_auth section (introduced in release  1.16)  controls  modules
       for  the  kadmin  authorization  interface,  which determines whether a
       client principal is allowed to perform a kadmin operation.  The follow-
       ing built-in modules exist for this interface:

       acl    This  module  reads the kadm5.acl(5) file, and authorizes opera-
              tions which are allowed according to the rules in the file.

       self   This module authorizes self-service operations  including  pass-
              word changes, creation of new random keys, fetching the client's
              principal record or string attributes, and fetching  the  policy
              record associated with the client principal.

   clpreauth and kdcpreauth interfaces
       The clpreauth and kdcpreauth interfaces allow plugin modules to provide
       client and KDC preauthentication mechanisms.   The  following  built-in
       modules exist for these interfaces:

       pkinit This module implements the PKINIT preauthentication mechanism.

       encrypted_challenge
              This module implements the encrypted challenge FAST factor.

       encrypted_timestamp
              This module implements the encrypted timestamp mechanism.

   hostrealm interface
       The hostrealm section (introduced in release 1.12) controls modules for
       the host-to-realm interface, which affects the local mapping  of  host-
       names  to  realm  names and the choice of default realm.  The following
       built-in modules exist for this interface:

       profile
              This module consults the [domain_realm] section of  the  profile
              for  authoritative host-to-realm mappings, and the default_realm
              variable for the default realm.

       dns    This module looks for DNS  records  for  fallback  host-to-realm
              mappings  and  the  default  realm.   It  only  operates  if the
              dns_lookup_realm variable is set to true.

       domain This module applies heuristics for fallback  host-to-realm  map-
              pings.   It  implements the realm_try_domains variable, and uses
              the uppercased parent domain of the hostname if  that  does  not
              produce a result.

   localauth interface
       The localauth section (introduced in release 1.12) controls modules for
       the local  authorization  interface,  which  affects  the  relationship
       between  Kerberos  principals and local system accounts.  The following
       built-in modules exist for this interface:

       default
              This module implements the DEFAULT type for  auth_to_local  val-
              ues.

       rule   This module implements the RULE type for auth_to_local values.

       names  This  module  looks  for  an auth_to_local_names mapping for the
              principal name.

       auth_to_local
              This  module  processes  auth_to_local  values  in  the  default
              realm's   section,   and   applies  the  default  method  if  no
              auth_to_local values exist.

       k5login
              This module authorizes a principal to a local account  according
              to the account's .k5login(5) file.

       an2ln  This  module  authorizes  a  principal to a local account if the
              principal name maps to the local account name.

   certauth interface
       The certauth section (introduced in release 1.16) controls modules  for
       the  certificate  authorization  interface,  which determines whether a
       certificate is allowed to preauthenticate a user via PKINIT.  The  fol-
       lowing built-in modules exist for this interface:

       pkinit_san
              This  module  authorizes the certificate if it contains a PKINIT
              Subject Alternative Name for the requested client principal,  or
              a  Microsoft  UPN SAN matching the principal if pkinit_allow_upn
              is set to true for the realm.

       pkinit_eku
              This module rejects the certificate if it does  not  contain  an
              Extended    Key    Usage    attribute    consistent   with   the
              pkinit_eku_checking value for the realm.

       dbmatch
              This module authorizes or rejects the certificate  according  to
              whether it matches the pkinit_cert_match string attribute on the
              client principal, if that attribute is present.


PKINIT OPTIONS

       NOTE:
          The following are PKINIT-specific  options.   These  values  may  be
          specified   in   [libdefaults]  as  global  defaults,  or  within  a
          realm-specific subsection of [libdefaults], or may be  specified  as
          realm-specific  values  in  the  [realms] section.  A realm-specific
          value overrides, not adds to, a generic [libdefaults] specification.
          The search order is:

       1. realm-specific subsection of [libdefaults]:

             [libdefaults]
                 EXAMPLE.COM = {
                     pkinit_anchors = FILE:/usr/local/example.com.crt
                 }

       2. realm-specific value in the [realms] section:

             [realms]
                 OTHERREALM.ORG = {
                     pkinit_anchors = FILE:/usr/local/otherrealm.org.crt
                 }

       3. generic value in the [libdefaults] section:

             [libdefaults]
                 pkinit_anchors = DIR:/usr/local/generic_trusted_cas/

   Specifying PKINIT identity information
       The  syntax  for  specifying Public Key identity, trust, and revocation
       information for PKINIT is as follows:

       FILE:filename[,keyfilename]
              This option has context-specific behavior.

              In pkinit_identity or pkinit_identities, filename specifies  the
              name of a PEM-format file containing the user's certificate.  If
              keyfilename is not specified, the user's private key is expected
              to  be  in filename as well.  Otherwise, keyfilename is the name
              of the file containing the private key.

              In pkinit_anchors or pkinit_pool, filename is assumed to be  the
              name of an OpenSSL-style ca-bundle file.

       DIR:dirname
              This option has context-specific behavior.

              In  pkinit_identity  or  pkinit_identities,  dirname specifies a
              directory with files named *.crt and *.key where the first  part
              of  the  file name is the same for matching pairs of certificate
              and private key files.  When a file with a name ending with .crt
              is found, a matching file ending with .key is assumed to contain
              the private key.  If no such file is found, then the certificate
              in the .crt is not used.

              In  pkinit_anchors  or  pkinit_pool, dirname is assumed to be an
              OpenSSL-style hashed CA directory where each CA cert  is  stored
              in  a  file  named  hash-of-ca-cert.#.   This  infrastructure is
              encouraged, but all files in the directory will be examined  and
              if they contain certificates (in PEM format), they will be used.

              In pkinit_revoke, dirname is  assumed  to  be  an  OpenSSL-style
              hashed  CA  directory  where each revocation list is stored in a
              file named hash-of-ca-cert.r#.  This infrastructure  is  encour-
              aged,  but  all  files  in the directory will be examined and if
              they contain a revocation list (in PEM  format),  they  will  be
              used.

       PKCS12:filename
              filename  is  the name of a PKCS #12 format file, containing the
              user's certificate and private key.

       PKCS11:[module_name=]modname[:slotid=slot-id][:token=token-label][:cer-
       tid=cert-id][:certlabel=cert-label]
              All keyword/values are optional.  modname specifies the location
              of  a  library implementing PKCS #11.  If a value is encountered
              with no keyword, it is assumed to be the modname.   If  no  mod-
              ule-name is specified, the default is opensc-pkcs11.so.  slotid=
              and/or token= may be specified to force the use of a  particular
              smard  card reader or token if there is more than one available.
              certid= and/or certlabel= may be specified to force  the  selec-
              tion  of  a  particular  certificate  on  the  device.   See the
              pkinit_cert_match configuration option for more ways to select a
              particular certificate to use for PKINIT.

       ENV:envvar
              envvar  specifies  the name of an environment variable which has
              been set to a value conforming to one of  the  previous  values.
              For   example,   ENV:X509_PROXY,   where   environment  variable
              X509_PROXY has been set to FILE:/tmp/my_proxy.pem.

   PKINIT krb5.conf options
       pkinit_anchors
              Specifies the location of  trusted  anchor  (root)  certificates
              which  the  client trusts to sign KDC certificates.  This option
              may be specified multiple times.  These values from  the  config
              file are not used if the user specifies X509_anchors on the com-
              mand line.

       pkinit_cert_match
              Specifies matching rules that the client certificate must  match
              before  it  is used to attempt PKINIT authentication.  If a user
              has multiple certificates available (on a  smart  card,  or  via
              other  media),  there  must  be  exactly  one certificate chosen
              before attempting PKINIT authentication.   This  option  may  be
              specified  multiple  times.   All the available certificates are
              checked against each rule in order until there  is  a  match  of
              exactly one certificate.

              The  Subject  and  Issuer  comparison  strings  are the RFC 2253
              string representations  from  the  certificate  Subject  DN  and
              Issuer DN values.

              The syntax of the matching rules is:
                 [relation-operator]component-rule ...

              where:

              relation-operator
                     can be either &&, meaning all component rules must match,
                     or ||, meaning only one component rule must  match.   The
                     default is &&.

              component-rule
                     can be one of the following.  Note that there is no punc-
                     tuation or whitespace between component rules.
                        <SUBJECT>regular-expression
                        <ISSUER>regular-expression
                        <SAN>regular-expression
                        <EKU>extended-key-usage-list
                        <KU>key-usage-list


                     extended-key-usage-list  is  a  comma-separated  list  of
                     required  Extended  Key  Usage values.  All values in the
                     list must be present in the  certificate.   Extended  Key
                     Usage values can be:

                     o pkinit

                     o msScLogin

                     o clientAuth

                     o emailProtection

                     key-usage-list  is a comma-separated list of required Key
                     Usage values.  All values in the list must be present  in
                     the certificate.  Key Usage values can be:

                     o digitalSignature

                     o keyEncipherment

              Examples:

                 pkinit_cert_match = ||<SUBJECT>.*DoE.*<SAN>.*@EXAMPLE.COM
                 pkinit_cert_match = &&<EKU>msScLogin,clientAuth<ISSUER>.*DoE.*
                 pkinit_cert_match = <EKU>msScLogin,clientAuth<KU>digitalSignature

       pkinit_eku_checking
              This option specifies what Extended Key Usage value the KDC cer-
              tificate presented to the client must contain.   (Note  that  if
              the   KDC  certificate  has  the  pkinit  SubjectAlternativeName
              encoded as the Kerberos TGS name, EKU checking is not  necessary
              since  the  issuing CA has certified this as a KDC certificate.)
              The values recognized in the krb5.conf file are:

              kpKDC  This is the default value and specifies that the KDC must
                     have the id-pkinit-KPKdc EKU as defined in RFC 4556.

              kpServerAuth
                     If  kpServerAuth is specified, a KDC certificate with the
                     id-kp-serverAuth EKU will be accepted.   This  key  usage
                     value is used in most commercially issued server certifi-
                     cates.

              none   If none is specified, then the KDC certificate  will  not
                     be  checked  to verify it has an acceptable EKU.  The use
                     of this option is not recommended.

       pkinit_dh_min_bits
              Specifies the size of the Diffie-Hellman  key  the  client  will
              attempt to use.  The acceptable values are 1024, 2048, and 4096.
              The default is 2048.

       pkinit_identities
              Specifies the location(s) to be used to find  the  user's  X.509
              identity  information.   If  this  option  is specified multiple
              times, each value is attempted in order until  certificates  are
              found.   Note  that these values are not used if the user speci-
              fies X509_user_identity on the command line.

       pkinit_kdc_hostname
              The presence of this option indicates that the client is willing
              to accept a KDC certificate with a dNSName SAN (Subject Alterna-
              tive Name) rather than requiring the id-pkinit-san as defined in
              RFC  4556.   This  option  may be specified multiple times.  Its
              value should contain the acceptable hostname  for  the  KDC  (as
              contained in its certificate).

       pkinit_pool
              Specifies the location of intermediate certificates which may be
              used by the client to complete the trust  chain  between  a  KDC
              certificate  and a trusted anchor.  This option may be specified
              multiple times.

       pkinit_require_crl_checking
              The default certificate verification process will  always  check
              the available revocation information to see if a certificate has
              been revoked.  If a match is found for the certificate in a CRL,
              verification  fails.   If  the certificate being verified is not
              listed in a CRL, or there is no CRL present for its issuing  CA,
              and pkinit_require_crl_checking is false, then verification suc-
              ceeds.

              However, if pkinit_require_crl_checking is true and there is  no
              CRL  information available for the issuing CA, then verification
              fails.

              pkinit_require_crl_checking should be set to true if the  policy
              is such that up-to-date CRLs must be present for every CA.

       pkinit_revoke
              Specifies  the  location  of  Certificate  Revocation List (CRL)
              information to be used by the client when verifying the validity
              of  the KDC certificate presented.  This option may be specified
              multiple times.


PARAMETER EXPANSION

       Starting   with   release   1.11,   several    variables,    such    as
       default_keytab_name, allow parameters to be expanded.  Valid parameters
       are:

                    +------------------+----------------------------+
                    |%{TEMP}           | Temporary directory        |
                    +------------------+----------------------------+
                    |%{uid}            | Unix real UID  or  Windows |
                    |                  | SID                        |
                    +------------------+----------------------------+
                    |%{euid}           | Unix  effective user ID or |
                    |                  | Windows SID                |
                    +------------------+----------------------------+
                    |%{USERID}         | Same as %{uid}             |
                    +------------------+----------------------------+
                    |%{null}           | Empty string               |
                    +------------------+----------------------------+
                    |%{LIBDIR}         | Installation       library |
                    |                  | directory                  |
                    +------------------+----------------------------+
                    |%{BINDIR}         | Installation binary direc- |
                    |                  | tory                       |
                    +------------------+----------------------------+
                    |%{SBINDIR}        | Installation admin  binary |
                    |                  | directory                  |
                    +------------------+----------------------------+
                    |%{username}       | (Unix)  Username of effec- |
                    |                  | tive user ID               |
                    +------------------+----------------------------+
                    |%{APPDATA}        | (Windows) Roaming applica- |
                    |                  | tion data for current user |
                    +------------------+----------------------------+
                    |%{COMMON_APPDATA} | (Windows) Application data |
                    |                  | for all users              |
                    +------------------+----------------------------+
                    |%{LOCAL_APPDATA}  | (Windows)  Local  applica- |
                    |                  | tion data for current user |
                    +------------------+----------------------------+


                    |%{SYSTEM}         | (Windows)  Windows  system |
                    |                  | folder                     |
                    +------------------+----------------------------+
                    |%{WINDOWS}        | (Windows) Windows folder   |
                    +------------------+----------------------------+
                    |%{USERCONFIG}     | (Windows)   Per-user   MIT |
                    |                  | krb5 config file directory |
                    +------------------+----------------------------+
                    |%{COMMONCONFIG}   | (Windows) Common MIT  krb5 |
                    |                  | config file directory      |
                    +------------------+----------------------------+


SAMPLE KRB5.CONF FILE

       Here is an example of a generic krb5.conf file:

          [libdefaults]
              default_realm = ATHENA.MIT.EDU
              dns_lookup_kdc = true
              dns_lookup_realm = false

          [realms]
              ATHENA.MIT.EDU = {
                  kdc = kerberos.mit.edu
                  kdc = kerberos-1.mit.edu
                  kdc = kerberos-2.mit.edu
                  admin_server = kerberos.mit.edu
                  primary_kdc = kerberos.mit.edu
              }
              EXAMPLE.COM = {
                  kdc = kerberos.example.com
                  kdc = kerberos-1.example.com
                  admin_server = kerberos.example.com
              }

          [domain_realm]
              mit.edu = ATHENA.MIT.EDU

          [capaths]
              ATHENA.MIT.EDU = {
                     EXAMPLE.COM = .
              }
              EXAMPLE.COM = {
                     ATHENA.MIT.EDU = .
              }


FILES

       /etc/krb5.conf


SEE ALSO

       syslog(3)


AUTHOR

       MIT


COPYRIGHT

       1985-2021, MIT



1.19.1                                                            krb5.conf(5)

kerberos5 1.19.1 - Generated Tue Mar 9 16:32:21 CST 2021
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