--- name: "krb5.conf" section: "5heimdal" platform: "linux" package: "heimdal-docs" version: "7.8.git20221117.28daf24+dfsg-9+deb13u1" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/krb5.conf/5heimdal" --- # krb5.conf(5heimdal) configuration file for Kerberos 5 ## NAME **krb5.conf** – configuration file for Kerberos 5 ## SYNOPSIS **#include \** ## 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)](/rsh/1.md), [telnet(1)](/telnet/1.md), etc). - historical\_anon\_pkinit = *boolean* Enable legacy anonymous pkinit command-line syntax. With this option set to true, the [kinit(1)](/kinit/1.md) **-****-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)](/su/1.md), 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)](/strftime/3.md). - date\_format = *string* How to print date strings in logs, this string is passed to [strftime(3)](/strftime/3.md). - 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)](/krb5_rd_req/3.md), 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)](/krb5_openlog/3.md) 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. ## SEE ALSO [kinit(1)](/kinit/1.md), [krb5\_openlog(3)](/krb5_openlog/3.md), [strftime(3)](/strftime/3.md), [verify\_krb5\_conf(8)](/verify_krb5_conf/8.md)