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heimdal-krb5.conf - Man Page

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 */

	section sections

	'[' section_name ']' bindings


	binding bindings

	name '=' STRING
	name '=' '{' bindings '}'


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.


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).

historical_anon_pkinit = boolean

Enable legacy anonymous pkinit command-line syntax. With this option set to true, the kinit(1) --anonymous command with no principal argument specified will request an anonymous pkinit ticket from the default realm. If a principal argument is specified, it is used as an explicit realm name for anonymous pkinit even without an @ prefix.

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

are weak 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.

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. The Only supported variable currently is %{uid} which 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.

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 makes it store the MIT way, this is default for Heimdal 0.7.


If set to "ignore", the framework will ignore any of 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.

k5login_directory = directory

Alternative location for user .k5login files. This option is provided for compatibility with MIT krb5 configuration files.

k5login_authoritative = boolean

If true then if a principal is not found in k5login files then krb5_userok(3) will not fallback on principal to username mapping. This option is provided for compatibility with MIT krb5 configuration files.

kuserok = rule ...

Specifies krb5_userok(3) behavior. If multiple values are given, then krb5_userok(3) will evaluate them in order until one succeeds or all fail. Rules are implemented by plugins, with three built-in plugins described below. Default: USER-K5LOGIN SIMPLE DENY.

kuserok = DENY

If set and evaluated then krb5_userok(3) will deny access to the given username no matter what the principal name might be.

kuserok = SIMPLE

If set and evaluated then krb5_userok(3) will use principal to username mapping (see auth_to_local below). If the principal maps to the requested username then access is allowed.

kuserok = SYSTEM-K5LOGIN[:directory]

If set and evaluated then krb5_userok(3) will use k5login files named after the luser argument to krb5_userok(3) in the given directory or in /etc/k5login.d/. K5login files are text files, with each line containing just a principal name; principals apearing in a user's k5login file are permitted access to the user's account. Note: this rule performs no ownership nor permissions checks on k5login files; proper ownership and permissions/ACLs are expected due to the k5login location being a system location.

kuserok = USER-K5LOGIN

If set and evaluated then krb5_userok(3) will use ~luser/.k5login and ~luser/.k5login.d/*. User k5login files and directories must be owned by the user and must not have world nor group write permissions.

aname2lname-text-db = filename

The named file must be a sorted (in increasing order) text file where every line consists of an unparsed principal name optionally followed by whitespace and a username. The aname2lname function will do a binary search on this file, if configured, looking for lines that match the given principal name, and if found the given username will be used, or, if the username is missing, an error will be returned. If the file doesn't exist, or if no matching line is found then other plugins will be allowed to run.


strict checking in FILE credential caches that owner, no symlink and permissions is correct.

name_canon_rules = rules

One or more service principal name canonicalization rules. Each rule consists of one or more tokens separated by colon (':'). Currently these rules are used only for hostname canonicalization (usually when getting a service ticket, from a ccache or a TGS, but also when acquiring GSS initiator credentials from a keytab). These rules can be used to implement DNS resolver-like search lists without having to use DNS.

NOTE: Name canonicalization rules are an experimental feature.

The first token is a rule type, one of: as-is, qualify, or nss.

Any remaining tokens must be options tokens: use_fast (use FAST to protect TGS exchanges; currently not supported), use_dnssec (use DNSSEC to protect hostname lookups; currently not supported), ccache_only , use_referrals, no_referrals, lookup_realm, mindots=N, maxdots=N, order=N, domain= domain, realm= realm, match_domain= domain, and match_realm= realm.

When trying to obtain a service ticket for a host-based service principal name, name canonicalization rules are applied to that name in the order given, one by one, until one succeds (a service ticket is obtained), or all fail. Similarly when acquiring GSS initiator credentials from a keytab, and when comparing a non-canonical GSS name to a canonical one.

For each rule the system checks that the hostname has at least mindots periods (if given) in it, at most maxdots periods (if given), that the hostname ends in the given match_domain (if given), and that the realm of the principal matches the match_realm (if given).

As-is rules leave the hostname unmodified but may set a realm. Qualify rules qualify the hostname with the given domain and also may set the realm. The nss rule uses the system resolver to lookup the host's canonical name and is usually not secure. Note that using the nss rule type implies having to have principal aliases in the HDB (though not necessarily in keytabs).

The empty realm denotes "ask the client's realm's TGS". The empty realm may be set as well as matched.

The order in which rules are applied is as follows: first all the rules with explicit order then all other rules in the order in which they appear. If any two rules have the same explicit order, their order of appearance in krb5.conf breaks the tie. Explicitly specifying order can be useful where tools read and write the configuration file without preserving parameter order.

Malformed rules are ignored.

allow_hierarchical_capaths = boolean

When validating cross-realm transit paths, absent any explicit capath from the client realm to the server realm, allow a hierarchical transit path via the common ancestor domain of the two realms. Defaults to true. Note, absent an explicit setting, hierarchical capaths are always used by the KDC when generating a referral to a destination with which is no direct trust.


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.


a boolan variable that defaults to false. Old DCE secd (pre 1.1) might need this to be true.

auth_to_local_names = {
principal_name = username

The given principal_name will be mapped to the given username if the REALM is a default realm.

auth_to_local = HEIMDAL_DEFAULT

Use the Heimdal default principal to username mapping. Applies to principals from the REALM if and only if REALM is a default realm.

auth_to_local = DEFAULT

Use the MIT default principal to username mapping. Applies to principals from the REALM if and only if REALM is a default realm.

auth_to_local = DB:/path/to/db.txt

Use a binary search of the given DB. The DB must be a flat-text file sortedf in the "C" locale, with each record being a line (separated by either LF or CRLF) consisting of a principal name followed by whitespace followed by a username. Applies to principals from the REALM if and only if REALM is a default realm.

auth_to_local = DB:/path/to/db

Use the given DB, if there's a plugin for it. Applies to principals from the REALM if and only if REALM is a default realm.

auth_to_local = RULE:...

Use the given rule, if there's a plugin for it. Applies to principals from the REALM if and only if REALM is a default realm.

auth_to_local = NONE

No additional principal to username mapping is done. Note that auth_to_local_names and any preceding auth_to_local rules have precedence.

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. The DATABASETYPE should be one of 'lmdb', 'db3', 'db1', 'db', 'sqlite', or 'ldap'. 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. It is also used by kadmind and kadmin (when used with the -l option), and by all applications using libkadm5 with the local backend, for two-phase commit functionality. Slaves also use this. Setting this to /dev/null disables two-phase commit and incremental propagation. Use iprop-log to show the contents of this log file.

log-max-size = number

When the log reaches this size (in bytes), the log will be truncated, saving some entries, and keeping the latest version number so as to not disrupt incremental propagation. If set to a negative value then automatic log truncation will be disabled. Defaults to 52428800 (50MB).

max-request = SIZE

Maximum size of a kdc request.

require-preauth = BOOL

If set pre-authentication is required.

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-http = BOOL

Should the kdc answer kdc-requests over http.

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 FALSE.

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 FALSE.

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 FALSE.

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.

historical_anon_realm = boolean

Enables pre-7.0 non-RFC-comformant KDC behavior. With this option set to true the client realm in anonymous pkinit AS replies will be the requested realm, rather than the RFC-conformant WELLKNOWN:ANONYMOUS realm. This can have a security impact on servers that expect to grant access to anonymous-but-authenticated to the KDC users of the realm in question: they would also grant access to unauthenticated anonymous users. As such, it is not recommend to set this option to true.

encode_as_rep_as_tgs_rep = BOOL

Encode as-rep as tgs-rep to be 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.

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.

kx509_ca = file

Specifies the PEM credentials for the kx509 certification authority.

require_initial_kca_tickets = boolean

Specified whether to require that tickets for the kca_service service principal be INITIAL. This may be set on a per-realm basis as well as globally. Defaults to true for the global setting.

kx509_include_pkinit_san = boolean

If true then the kx509 client principal's name and realm will be included in an id-pkinit-san certificate extension. This can be set on a per-realm basis as well as globally. Defaults to true for the global setting.

kx509_template = file

Specifies the PEM file with a template for the certificates to be issued. The following variables can be interpolated in the subject name using ${variable} syntax:


The full name of the kx509 client principal.


The full name of the kx509 client principal, excluding the realm name.


The name of the client principal's realm.

The kx509, kx509_template, kx509_include_pkinit_san, and require_initial_kca_tickets parameters may be set on a per-realm basis as well.

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:


The Kerberos 5 salt pw-salt

default_key_rules = {
globing-rule = keytypes...

a globbing rule to matching a principal, and when true, use the keytypes as specified the same format as [kadmin]default_keys .

prune-key-history = BOOL

When adding keys to the key history, drop keys that are too old to match unexpired tickets (based on the principal's maximum ticket lifetime). If the KDC keystore is later compromised traffic protected with the discarded older keys may remain protected. This also keeps the HDB records for principals with key history from growing without bound. The default (backwards compatible) value is "false".

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
	name_canon_rules = as-is:realm=FOO.SE
	name_canon_rules = qualify:domain=foo.se:realm=FOO.SE
	name_canon_rules = qualify:domain=bar.se:realm=FOO.SE
	name_canon_rules = nss
	.foo.se = FOO.SE
	.bar.se = FOO.SE
	FOO.SE = {
		kdc = kerberos.foo.se
		default_domain = foo.se
	kdc = FILE:/var/heimdal/kdc.log
	default_key_rules = {
		*/ppp@* = arcfour-hmac-md5:pw-salt


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.

See Also

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


May 4, 2005