Ubuntu Manpage: krb5.conf — configuration file for Kerberos 5

Provided by: heimdal-docs_7.8.git20221117.28daf24+dfsg-9ubuntu1_all

NAME

       krb5.conf — configuration file for Kerberos 5

SYNOPSIS

       #include <krb5.h>

DESCRIPTION

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:

file:
/* empty */
sections
includes

sections:
section sections
section

section:
'[' section_name ']' bindings

section_name:
STRING

bindings:
binding bindings
binding

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

name:
STRING

includes:
'include' path
'includedir' path

path: STRING

STRINGs consists of one or more non-whitespace characters.

Files and directories may be included by absolute path. Including a directory causes all files in the
directory to be included as if each file had been included separately, but only files whose names consist
of alphanumeric, hyphen, and underscore are included, though they may also end in '.conf'.

STRINGs that are specified later in this man-page uses the following notation.

boolean
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.

etypes
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 .

address
an address can be either a IPv4 or a IPv6 address.

Currently recognised sections and bindings are:

[appdefaults]
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.

[libdefaults]

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.

check-rd-req-server
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.

fcache_strict_checking
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.

[domain_realm]
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).

[realms]

REALM = {

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.

tgs_require_subkey
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.

}

[capaths]

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.

}

[logging]

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.

[kdc]

database = {

dbname = [DATBASETYPE:]DATABASENAME
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:

principal-name
The full name of the kx509 client principal.

principal-name-without-realm
The full name of the kx509 client principal, excluding the realm name.

principal-name-realm
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.

[kadmin]

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:

[(des|des3|etype):](pw-salt|afs3-salt)[:string]

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

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.

[password_quality]
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.

ENVIRONMENT

       KRB5_CONFIG points to the configuration file to read.

FILES

       /etc/krb5.conf  configuration file for Kerberos 5.

EXAMPLES

             [libdefaults]
                     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
             [domain_realm]
                     .foo.se = FOO.SE
                     .bar.se = FOO.SE
             [realms]
                     FOO.SE = {
                             kdc = kerberos.foo.se
                             default_domain = foo.se
                     }
             [logging]
                     kdc = FILE:/var/heimdal/kdc.log
                     kdc = SYSLOG:INFO
                     default = SYSLOG:INFO:USER
             [kadmin]
                     default_key_rules = {
                             */ppp@* = arcfour-hmac-md5:pw-salt
                     }

DIAGNOSTICS

       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.