KRB5.CONF(5) File Formats Manual KRB5.CONF(5)
NAME
krb5.conf - Kerberos configuration file
DESCRIPTION
krb5.conf contains configuration information needed by the Kerberos V5 library. This includes information describing the default Kerberos
realm, and the location of the Kerberos key distribution centers for known realms.
The krb5.conf file uses an INI-style format. Sections are delimited by square braces; within each section, there are relations where tags
can be assigned to have specific values. Tags can also contain a subsection, which contains further relations or subsections. A tag can
be assigned to multiple values. Here is an example of the INI-style format used by krb5.conf:
[section1]
tag1 = value_a
tag1 = value_b
tag2 = value_c
[section 2]
tag3 = {
subtag1 = subtag_value_a
subtag1 = subtag_value_b
subtag2 = subtag_value_c
}
tag4 = {
subtag1 = subtag_value_d
subtag2 = subtag_value_e
}
The following sections are currently used in the krb5.conf file:
[libdefaults]
Contains various default values used by the Kerberos V5 library.
[login]
Contains default values used by the Kerberos V5 login program, login.krb5(8).
[realms]
Contains subsections keyed by Kerberos realm names which describe where to find the Kerberos servers for a particular realm, and
other realm-specific information.
[domain_realm]
Contains relations which map subdomains and domain names to Kerberos realm names. This is used by programs to determine what realm
a host should be in, given its fully qualified domain name.
[logging]
Contains relations which determine how Kerberos entities are to perform their logging.
[capaths]
Contains the authentication paths used with non-hierarchical cross-realm. Entries in the section are used by the client to determine
the intermediate realms which may be used in cross-realm authentication. It is also used by the end-service when checking the tran-
sited field for trusted intermediate realms.
Each of these sections will be covered in more details in the following sections.
LIBDEFAULTS SECTION
The following relations are defined in the [libdefaults] section:
default_keytab_name
This relation specifies the default keytab name to be used by application severs such as telnetd and rlogind. The default is
"/etc/krb5.keytab". This formerly defaulted to "/etc/v5srvtab", but was changed to the current value.
default_realm
This relation identifies the default realm to be used in a client host's Kerberos activity.
default_tgs_enctypes
This relation identifies the supported list of session key encryption types that should be returned by the KDC. The list may be
delimited with commas or whitespace.
default_tkt_enctypes
This relation identifies the supported list of session key encryption types that should be requested by the client, in the same for-
mat.
clockskew
This relation sets the maximum allowable amount of clockskew in seconds that the library will tolerate before assuming that a Ker-
beros message is invalid. The default value is 300 seconds, or five minutes.
kdc_timesync
If the value of this relation is non-zero, the library will compute the difference between the system clock and the time returned by
the KDC and in order to correct for an inaccurate system clock. This corrective factor is only used by the Kerberos library.
kdc_req_checksum_type
For compatability with DCE security servers which do not support the default CKSUMTYPE_RSA_MD5 used by this version of Kerberos. Use
a value of 2 to use the CKSUMTYPE_RSA_MD4 instead. This applies to DCE 1.1 and earlier.
ap_req_checksum_type
This allows you to set the checksum type used in the authenticator of KRB_AP_REQ messages. The default value for this type is
CKSUMTYPE_RSA_MD5. For compatibility with applications linked against DCE version 1.1 or earlier Kerberos libraries, use a value of
2 to use the CKSUMTYPE_RSA_MD4 instead.
safe_checksum_type
This allows you to set the preferred keyed-checksum type for use in KRB_SAFE messages. The default value for this type is CKSUM-
TYPE_RSA_MD5_DES. For compatibility with applications linked against DCE version 1.1 or earlier Kerberos libraries, use a value of
3 to use the CKSUMTYPE_RSA_MD4_DES instead. This field is ignored when its value is incompatible with the session key type.
ccache_type
User this parameter on systems which are DCE clients, to specify the type of cache to be created by kinit, or when forwarded tickets
are received. DCE and Kerberos can share the cache, but some versions of DCE do not support the default cache as created by this
version of Kerberos. Use a value of 1 on DCE 1.0.3a systems, and a value of 2 on DCE 1.1 systems.
LOGIN SECTION
The [login] section is used to configure the behavior of the Kerberos V5 login program, login.krb5(8). Refer to the manual entry for
login.krb5 for a description of the relations allowed in this section.
REALMS SECTION
Each tag in the [realms] section of the file names a Kerberos realm. The value of the tag is a subsection where the relations in that sub-
section define the properties of that particular realm. For example:
[realms]
ATHENA.MIT.EDU = {
kdc = KERBEROS.MIT.EDU
kdc = KERBEROS-1.MIT.EDU:750
kdc = KERBEROS-2.MIT.EDU:88
admin_server = KERBEROS.MIT.EDU
default_domain = MIT.EDU
v4_instance_convert = {
mit = mit.edu
lithium = lithium.lcs.mit.edu
}
v4_realm = LCS.MIT.EDU
}
For each realm, the following tags may be specified in the realm's subsection:
kdc The value of this relation is the name of a host running a KDC for that realm. An optional port number (preceded by a colon) may be
appended to the hostname.
admin_server
This relation identifies the host where the administration server is running. Typically this is the Master Kerberos server.
default_domain
This relation identifies the default domain for which hosts in this realm are assumed to be in. This is needed for translating V4
principal names (which do not contain a domain name) to V5 principal names (which do).
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 hostname (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 converting a V5 principal name to a V4 principal name. It is used when V4
realm name and the V5 realm are not the same, but still share the same principal names and passwords. The tag value is the Kerberos
V4 realm name.
DOMAIN_REALM SECTION
The [domain_realm] section provides a translation from a hostname to the Kerberos realm name for the services provided by that host.
The tag name can be a hostname, or a domain name, where domain names are indicated by a prefix of a period ('.') character. The value of
the relation is the Kerberos realm name for that particular host or domain. Host names and domain names should be in lower case.
If no translation entry applies, the host's realm is considered to be the hostname's domain portion converted to upper case. For example,
the following [domain_realm] section:
[domain_realm]
.mit.edu = ATHENA.MIT.EDU
mit.edu = ATHENA.MIT.EDU
dodo.mit.edu = SMS_TEST.MIT.EDU
.ucsc.edu = CATS.UCSC.EDU
maps dodo.mit.edu into the SMS_TEST.MIT.EDU realm, all other hosts in the MIT.EDU domain to the ATHENA.MIT.EDU realm, and all hosts in the
UCSC.EDU domain into the CATS.UCSC.EDU realm. ucbvax.berkeley.edu would be mapped by the default rules to the BERKELEY.EDU realm, while
sage.lcs.mit.edu would be mapped to the LCS.MIT.EDU realm.
LOGGING SECTION
The [logging] section indicates how a particular entity is to perform its logging. The relations specified in this section assign one or
more values to the entity name.
Currently, the following entities are used:
kdc These entries specify how the KDC is to perform its logging.
admin_server
These entries specify how the administrative server is to perform its logging.
default
These entries specify how to perform logging in the absence of explicit specifications otherwise.
Values are of the following forms:
FILE=<filename>
FILE:<filename>
This value causes the entity's logging messages to go to the specified file. If the = form is used, then the file is overwritten.
Otherwise, the file is appended to.
STDERR This value causes the entity's logging messages to go to its standard error stream.
CONSOLE
This value causes the entity's logging messages to go to the console, if the system supports it.
DEVICE=<devicename>
This causes the entity's logging messages to go to the specified device.
SYSLOG[:<severity>[:<facility>]]
This causes the entity's logging messages to go to the system log.
The severity argument specifies the default severity of system log messages. This may be any of the following severities supported
by the syslog(3) call minus the LOG_ prefix: LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR, LOG_WARNING, LOG_NOTICE, LOG_INFO, and
LOG_DEBUG. For example, to specify LOG_CRIT severity, one would use CRIT for severity.
The facility argument specifies the facility under which the messages are logged. This may be any of the following facilities sup-
ported by the syslog(3) call minus the LOG_ prefix: LOG_KERN, LOG_USER, LOG_MAIL, LOG_DAEMON, LOG_AUTH, LOG_LPR, LOG_NEWS, LOG_UUCP,
LOG_CRON, and LOG_LOCAL0 through LOG_LOCAL7.
If no severity is specified, the default is ERR, and if no facility is specified, the default is AUTH.
In the following example, the logging messages from the KDC will go to the console and to the system log under the facility LOG_DAEMON with
default severity of LOG_INFO; and the logging messages from the administrative server will be appended to the file /var/adm/kadmin.log and
sent to the device /dev/tty04.
[logging]
kdc = CONSOLE
kdc = SYSLOG:INFO:DAEMON
admin_server = FILE:/var/adm/kadmin.log
admin_server = DEVICE=/dev/tty04
CAPATHS SECTION
Cross-realm authentication is typically organized hierarchically. This hierarchy is based on the name of the realm, which thus imposes
restrictions on the choice of realm names, and on who may participate in a cross-realm authentication. A non hierarchical orgization may be
used, but requires a database to construct the authentication paths between the realms. This section defines that database.
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 be the client, by checking the transited field of the received ticket.
There is a tag name for each participating realm, and each tag has subtags for each of the realms. The value of the subtags is an interme-
diate realm which may participate in the cross-realm authentication. The subtags may be repeated if there is more then one intermediate
realm. A value of "." means that the two realms share keys directly, and no intermediate realms should be allowed to participate.
There are n**2 possible entries in this table, but only those entries which will be needed on the client or the server need to be present.
The client needs a tag for its local realm, with subtags for all the realms of servers it will need to authenticate with. A server needs a
tag for each realm of the clients it will serve.
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 [capath] 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 [capath] section of the configuration file used on NERSC.GOV systems 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
}
In the above examples, the ordering is not important, except when the same subtag name is used more then once. The client will use this to
determing the path. (It is not important to the server, since the transited field is not sorted.)
If this section is not present, or if the client or server cannot find a client/server path, then normal hierarchical orginization is
assumed.
This feature is not currently supported by DCE. DCE security servers can be used with Kerberized clients and servers, but versions prior to
DCE 1.1 did not fill in the transited field, and should be used with caution.
FILES
/etc/krb5.conf
SEE ALSO
syslog(3)
KRB5.CONF(5)