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Manual Pages  — KRB5.CONF


krb5.conf – configuration file for Kerberos 5



#include <krb5.h>


The krb5.conf file specifies several configuration parameters for the Kerberos 5 library, as well as for some programs.

The file consists of one or more sections, containing a number of bindings. The value of each binding can be either a string or a list of other bindings. The grammar looks like:

        /* empty */

sections:         section sections         section

section:         '[' section_name ']' bindings

section_name:         STRING

bindings:         binding bindings         binding

binding:         name '=' STRING         name '=' '{' bindings '}'

name:         STRING

STRINGs consists of one or more non-whitespace characters.

STRINGs that are specified later in this man-page uses the following notation.
  values can be either yes/true or no/false.
time values can be a list of year, month, day, hour, min, second. Example: 1 month 2 days 30 min. If no unit is given, seconds is assumed.
  valid encryption types are: des-cbc-crc, des-cbc-md4, des-cbc-md5, des3-cbc-sha1, arcfour-hmac-md5, aes128-cts-hmac-sha1-96, and aes256-cts-hmac-sha1-96 .
  an address can be either a IPv4 or a IPv6 address.

Currently recognised sections and bindings are:
  Specifies the default values to be used for Kerberos applications. You can specify defaults per application, realm, or a combination of these. The preference order is:
  1. application realm option
  2. application option
  3. realm option
  4. option

The supported options are:

forwardable = boolean
  When obtaining initial credentials, make the credentials forwardable.
proxiable = boolean
  When obtaining initial credentials, make the credentials proxiable.
no-addresses = boolean
  When obtaining initial credentials, request them for an empty set of addresses, making the tickets valid from any address.
ticket_lifetime = time
  Default ticket lifetime.
renew_lifetime = time
  Default renewable ticket lifetime.
encrypt = boolean
  Use encryption, when available.
forward = boolean
  Forward credentials to remote host (for rsh(1), telnet(1), etc).
default_realm = REALM
  Default realm to use, this is also known as your "local realm". The default is the result of krb5_get_host_realm(local hostname).
allow_weak_crypto = boolean
  is weaks crypto algorithms allowed to be used, among others, DES is considered weak.
clockskew = time
  Maximum time differential (in seconds) allowed when comparing times. Default is 300 seconds (five minutes).
kdc_timeout = time
  Maximum time to wait for a reply from the kdc, default is 3 seconds.
  These are described in the krb5_425_conv_principal(3) manual page.
capath = {
destination-realm= next-hop-realm
This is deprecated, see the capaths section below.
default_cc_type = cctype
  sets the default credentials type.
default_cc_name = ccname
  the default credentials cache name. If you want to change the type only use default_cc_type. The string can contain variables that are expanded on runtime. Only support variable now is %{uid} that expands to the current user id.
default_etypes = etypes ...
  A list of default encryption types to use. (Default: all enctypes if allow_weak_crypto = TRUE, else all enctypes except single DES enctypes.)
default_as_etypes = etypes ...
  A list of default encryption types to use in AS requests. (Default: the value of default_etypes.)
default_tgs_etypes = etypes ...
  A list of default encryption types to use in TGS requests. (Default: the value of default_etypes.)
default_etypes_des = etypes ...
  A list of default encryption types to use when requesting a DES credential.
default_keytab_name = keytab
  The keytab to use if no other is specified, default is "FILE:/etc/krb5.keytab".
dns_lookup_kdc = boolean
  Use DNS SRV records to lookup KDC services location.
dns_lookup_realm = boolean
  Use DNS TXT records to lookup domain to realm mappings.
kdc_timesync = boolean
  Try to keep track of the time differential between the local machine and the KDC, and then compensate for that when issuing requests.
max_retries = number
  The max number of times to try to contact each KDC.
large_msg_size = number
  The threshold where protocols with tiny maximum message sizes are not considered usable to send messages to the KDC.
ticket_lifetime = time
  Default ticket lifetime.
renew_lifetime = time
  Default renewable ticket lifetime.
forwardable = boolean
  When obtaining initial credentials, make the credentials forwardable. This option is also valid in the [realms] section.
proxiable = boolean
  When obtaining initial credentials, make the credentials proxiable. This option is also valid in the [realms] section.
verify_ap_req_nofail = boolean
  If enabled, failure to verify credentials against a local key is a fatal error. The application has to be able to read the corresponding service key for this to work. Some applications, like su(1), enable this option unconditionally.
warn_pwexpire = time
  How soon to warn for expiring password. Default is seven days.
http_proxy = proxy-spec
  A HTTP-proxy to use when talking to the KDC via HTTP.
dns_proxy = proxy-spec
  Enable using DNS via HTTP.
extra_addresses = address ...
  A list of addresses to get tickets for along with all local addresses.
time_format = string
  How to print time strings in logs, this string is passed to strftime(3).
date_format = string
  How to print date strings in logs, this string is passed to strftime(3).
log_utc = boolean
  Write log-entries using UTC instead of your local time zone.
scan_interfaces = boolean
  Scan all network interfaces for addresses, as opposed to simply using the address associated with the system's host name.
fcache_version = int
  Use file credential cache format version specified.
krb4_get_tickets = boolean
  Also get Kerberos 4 tickets in kinit, login, and other programs. This option is also valid in the [realms] section.
fcc-mit-ticketflags = boolean
  Use MIT compatible format for file credential cache. It's the field ticketflags that is stored in reverse bit order for older than Heimdal 0.7. Setting this flag to TRUE make it store the MIT way, this is default for Heimdal 0.7.
  If set to "ignore", the framework will ignore any the server input to krb5_rd_req(3), this is very useful when the GSS-API server input the wrong server name into the gss_accept_sec_context call.
  This is a list of mappings from DNS domain to Kerberos realm. Each binding in this section looks like:

    domain = realm

The domain can be either a full name of a host or a trailing component, in the latter case the domain-string should start with a period. The trailing component only matches hosts that are in the same domain, ie ".example.com" matches "foo.example.com", but not "foo.test.example.com".

The realm may be the token `dns_locate', in which case the actual realm will be determined using DNS (independently of the setting of the `dns_lookup_realm' option).

kdc = [service/]host[:port]
  Specifies a list of kdcs for this realm. If the optional port is absent, the default value for the "kerberos/udp" "kerberos/tcp", and "http/tcp" port (depending on service) will be used. The kdcs will be used in the order that they are specified.

The optional service specifies over what medium the kdc should be contacted. Possible services are "udp", "tcp", and "http". Http can also be written as "http://". Default service is "udp" and "tcp".

admin_server = host[:port]
  Specifies the admin server for this realm, where all the modifications to the database are performed.
kpasswd_server = host[:port]
  Points to the server where all the password changes are performed. If there is no such entry, the kpasswd port on the admin_server host will be tried.
krb524_server = host[:port]
  Points to the server that does 524 conversions. If it is not mentioned, the krb524 port on the kdcs will be tried.
  See krb5_425_conv_principal(3).
  a boolan variable that defaults to false. Old DCE secd (pre 1.1) might need this to be true.
client-realm= {
server-realm= hop-realm ...
  This serves two purposes. First the first listed hop-realm tells a client which realm it should contact in order to ultimately obtain credentials for a service in the server-realm. Secondly, it tells the KDC (and other servers) which realms are allowed in a multi-hop traversal from client-realm to server-realm. Except for the client case, the order of the realms are not important.
entity= destination
  Specifies that entity should use the specified destination for logging. See the krb5_openlog(3) manual page for a list of defined destinations.
database= {
  Use this database for this realm. See the info documetation how to configure different database backends.
realm= REALM
  Specifies the realm that will be stored in this database. It realm isn't set, it will used as the default database, there can only be one entry that doesn't have a realm stanza.
mkey_file= FILENAME
  Use this keytab file for the master key of this database. If not specified DATABASENAME.mkey will be used.
acl_file= PA FILENAME
  Use this file for the ACL list of this database.
log_file= FILENAME
  Use this file as the log of changes performed to the database. This file is used by ipropd-master for propagating changes to slaves.
max-request = SIZE
  Maximum size of a kdc request.
require-preauth = BOOL
  If set pre-authentication is required. Since krb4 requests are not pre-authenticated they will be rejected.
ports = list of ports
  List of ports the kdc should listen to.
addresses = list of interfaces
  List of addresses the kdc should bind to.
enable-kerberos4 = BOOL
  Turn on Kerberos 4 support.
v4-realm = REALM
  To what realm v4 requests should be mapped.
enable-524 = BOOL
  Should the Kerberos 524 converting facility be turned on. Default is the same as enable-kerberos4.
enable-http = BOOL
  Should the kdc answer kdc-requests over http.
enable-kaserver = BOOL
  If this kdc should emulate the AFS kaserver.
tgt-use-strongest-session-key = BOOL
  If this is TRUE then the KDC will prefer the strongest key from the client's AS-REQ or TGS-REQ enctype list for the ticket session key that is supported by the KDC and the target principal when the target principal is a krbtgt principal. Else it will prefer the first key from the client's AS-REQ enctype list that is also supported by the KDC and the target principal. Defaults to TRUE.
svc-use-strongest-session-key = BOOL
  Like tgt-use-strongest-session-key, but applies to the session key enctype of tickets for services other than krbtgt principals. Defaults to TRUE.
preauth-use-strongest-session-key = BOOL
  If TRUE then select the strongest possible enctype from the client's AS-REQ for PA-ETYPE-INFO2 (i.e., for password-based pre-authentication). Else pick the first supported enctype from the client's AS-REQ. Defaults to TRUE.
use-strongest-server-key = BOOL
  If TRUE then the KDC picks, for the ticket encrypted part's key, the first supported enctype from the target service principal's hdb entry's current keyset. Else the KDC picks the first supported enctype from the target service principal's hdb entry's current keyset. Defaults to TRUE.
check-ticket-addresses = BOOL
  Verify the addresses in the tickets used in tgs requests.
allow-null-ticket-addresses = BOOL
  Allow address-less tickets.
allow-anonymous = BOOL
  If the kdc is allowed to hand out anonymous tickets.
encode_as_rep_as_tgs_rep = BOOL
  Encode as-rep as tgs-rep tobe compatible with mistakes older DCE secd did.
kdc_warn_pwexpire = TIME
  The time before expiration that the user should be warned that her password is about to expire.
logging = Logging
  What type of logging the kdc should use, see also [logging]/kdc.
use_2b = {
principal= BOOL
  boolean value if the 524 daemon should return AFS 2b tokens for principal.
hdb-ldap-structural-object structural object
  If the LDAP backend is used for storing principals, this is the structural object that will be used when creating and when reading objects. The default value is account .
hdb-ldap-create-base creation dn
  is the dn that will be appended to the principal when creating entries. Default value is the search dn.
enable-digest = BOOL
  Should the kdc answer digest requests. The default is FALSE.
digests_allowed = list of digests
  Specifies the digests the kdc will reply to. The default is ntlm-v2.
require-preauth = BOOL
  If pre-authentication is required to talk to the kadmin server.
password_lifetime = time
  If a principal already have its password set for expiration, this is the time it will be valid for after a change.
default_keys = keytypes...
  For each entry in default_keys try to parse it as a sequence of etype:salttype:salt syntax of this if something like:


If etype is omitted it means everything, and if string is omitted it means the default salt string (for that principal and encryption type). Additional special values of keytypes are:

v5 The Kerberos 5 salt pw-salt
v4 The Kerberos 4 salt des:pw-salt:
use_v4_salt = BOOL
  When true, this is the same as

default_keys = des3:pw-salt v4

and is only left for backwards compatibility.

  Check the Password quality assurance in the info documentation for more information.
check_library = library-name
  Library name that contains the password check_function
check_function = function-name
  Function name for checking passwords in check_library
policy_libraries = library1 ... libraryN
  List of libraries that can do password policy checks
policies = policy1 ... policyN
  List of policy names to apply to the password. Builtin policies are among other minimum-length, character-class, external-check.


KRB5_CONFIG points to the configuration file to read.


  configuration file for Kerberos 5.


        default_realm = FOO.SE
        .foo.se = FOO.SE
        .bar.se = FOO.SE
        FOO.SE = {
                kdc = kerberos.foo.se
                v4_name_convert = {
                        rcmd = host
                v4_instance_convert = {
                        xyz = xyz.bar.se
                default_domain = foo.se
        kdc = FILE:/var/heimdal/kdc.log
        kdc = SYSLOG:INFO
        default = SYSLOG:INFO:USER


Since krb5.conf is read and parsed by the krb5 library, there is not a lot of opportunities for programs to report parsing errors in any useful format. To help overcome this problem, there is a program verify_krb5_conf that reads krb5.conf and tries to emit useful diagnostics from parsing errors. Note that this program does not have any way of knowing what options are actually used and thus cannot warn about unknown or misspelled ones.


kinit(1), krb5_425_conv_principal(3), krb5_openlog(3), strftime(3), verify_krb5_conf(8)

HEIMDAL KRB5.CONF (5) May 4, 2005

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