1SSSD-KRB5(5) File Formats and Conventions SSSD-KRB5(5)
2
6 sssd-krb5 - SSSD Kerberos provider
7
9 This manual page describes the configuration of the Kerberos 5
10 authentication backend for sssd(8). For a detailed syntax reference,
11 please refer to the “FILE FORMAT” section of the sssd.conf(5) manual
12 page.
13 The Kerberos 5 authentication backend contains auth and chpass
15 providers. It must be paired with an identity provider in order to
16 function properly (for example, id_provider = ldap). Some information
17 required by the Kerberos 5 authentication backend must be provided by
18 the identity provider, such as the user's Kerberos Principal Name
19 (UPN). The configuration of the identity provider should have an entry
20 to specify the UPN. Please refer to the man page for the applicable
21 identity provider for details on how to configure this.
22 This backend also provides access control based on the .k5login file in
24 the home directory of the user. See k5login(5) for more details. Please
25 note that an empty .k5login file will deny all access to this user. To
26 activate this feature, use 'access_provider = krb5' in your SSSD
27 configuration.
28 In the case where the UPN is not available in the identity backend,
30 sssd will construct a UPN using the format username@krb5_realm.
31
33 If the auth-module krb5 is used in an SSSD domain, the following
34 options must be used. See the sssd.conf(5) manual page, section “DOMAIN
35 SECTIONS”, for details on the configuration of an SSSD domain.
36 krb5_server, krb5_backup_server (string)
38 Specifies the comma-separated list of IP addresses or hostnames of
39 the Kerberos servers to which SSSD should connect, in the order of
40 preference. For more information on failover and server redundancy,
41 see the “FAILOVER” section. An optional port number (preceded by a
42 colon) may be appended to the addresses or hostnames. If empty,
43 service discovery is enabled; for more information, refer to the
44 “SERVICE DISCOVERY” section.
45 When using service discovery for KDC or kpasswd servers, SSSD first
47 searches for DNS entries that specify _udp as the protocol and
48 falls back to _tcp if none are found.
49 This option was named “krb5_kdcip” in earlier releases of SSSD.
51 While the legacy name is recognized for the time being, users are
52 advised to migrate their config files to use “krb5_server” instead.
53 krb5_realm (string)
55 The name of the Kerberos realm. This option is required and must be
56 specified.
57 krb5_kpasswd, krb5_backup_kpasswd (string)
59 If the change password service is not running on the KDC,
60 alternative servers can be defined here. An optional port number
61 (preceded by a colon) may be appended to the addresses or
62 hostnames.
63 For more information on failover and server redundancy, see the
65 “FAILOVER” section. NOTE: Even if there are no more kpasswd servers
66 to try, the backend is not switched to operate offline if
67 authentication against the KDC is still possible.
68 Default: Use the KDC
70 krb5_ccachedir (string)
72 Directory to store credential caches. All the substitution
73 sequences of krb5_ccname_template can be used here, too, except %d
74 and %P. The directory is created as private and owned by the user,
75 with permissions set to 0700.
76 Default: /tmp
78 krb5_ccname_template (string)
80 Location of the user's credential cache. Three credential cache
81 types are currently supported: “FILE”, “DIR” and
82 “KEYRING:persistent”. The cache can be specified either as
83 TYPE:RESIDUAL, or as an absolute path, which implies the “FILE”
84 type. In the template, the following sequences are substituted:
85 %u
87 login name
88 %U
90 login UID
91 %p
93 principal name
94 %r
96 realm name
97 %h
99 home directory
100 %d
102 value of krb5_ccachedir
103 %P
105 the process ID of the SSSD client
106 %%
108 a literal '%'
109 If the template ends with 'XXXXXX' mkstemp(3) is used to create a
111 unique filename in a safe way.
112 When using KEYRING types, the only supported mechanism is
114 “KEYRING:persistent:%U”, which uses the Linux kernel keyring to
115 store credentials on a per-UID basis. This is also the recommended
116 choice, as it is the most secure and predictable method.
117 The default value for the credential cache name is sourced from the
119 profile stored in the system wide krb5.conf configuration file in
120 the [libdefaults] section. The option name is default_ccache_name.
121 See krb5.conf(5)'s PARAMETER EXPANSION paragraph for additional
122 information on the expansion format defined by krb5.conf.
123 NOTE: Please be aware that libkrb5 ccache expansion template from
125 krb5.conf(5) uses different expansion sequences than SSSD.
126 Default: (from libkrb5)
128 krb5_keytab (string)
130 The location of the keytab to use when validating credentials
131 obtained from KDCs.
132 Default: System keytab, normally /etc/krb5.keytab
134 krb5_store_password_if_offline (boolean)
136 Store the password of the user if the provider is offline and use
137 it to request a TGT when the provider comes online again.
138 NOTE: this feature is only available on Linux. Passwords stored in
140 this way are kept in plaintext in the kernel keyring and are
141 potentially accessible by the root user (with difficulty).
142 Default: false
144 krb5_use_fast (string)
146 Enables flexible authentication secure tunneling (FAST) for
147 Kerberos pre-authentication. The following options are supported:
148 never use FAST. This is equivalent to not setting this option at
150 all.
151 try to use FAST. If the server does not support FAST, continue the
153 authentication without it.
154 demand to use FAST. The authentication fails if the server does not
156 require fast.
157 Default: not set, i.e. FAST is not used.
159 NOTE: a keytab or support for anonymous PKINIT is required to use
161 FAST.
162 NOTE: SSSD supports FAST only with MIT Kerberos version 1.8 and
164 later. If SSSD is used with an older version of MIT Kerberos, using
165 this option is a configuration error.
166 krb5_fast_principal (string)
168 Specifies the server principal to use for FAST.
169 krb5_fast_use_anonymous_pkinit (boolean)
171 If set to true try to use anonymous PKINIT instead of a keytab to
172 get the required credential for FAST. The krb5_fast_principal
173 options is ignored in this case.
174 Default: false
176 krb5_use_kdcinfo (boolean)
178 Specifies if the SSSD should instruct the Kerberos libraries what
179 realm and which KDCs to use. This option is on by default, if you
180 disable it, you need to configure the Kerberos library using the
181 krb5.conf(5) configuration file.
182 See the sssd_krb5_locator_plugin(8) manual page for more
184 information on the locator plugin.
185 Default: true
187 krb5_kdcinfo_lookahead (string)
189 When krb5_use_kdcinfo is set to true, you can limit the amount of
190 servers handed to sssd_krb5_locator_plugin(8). This might be
191 helpful when there are too many servers discovered using SRV
192 record.
193 The krb5_kdcinfo_lookahead option contains two numbers separated by
195 a colon. The first number represents number of primary servers used
196 and the second number specifies the number of backup servers.
197 For example 10:0 means that up to 10 primary servers will be handed
199 to sssd_krb5_locator_plugin(8) but no backup servers.
200 Default: 3:1
202 krb5_use_enterprise_principal (boolean)
204 Specifies if the user principal should be treated as enterprise
205 principal. See section 5 of RFC 6806 for more details about
206 enterprise principals.
207 Default: false (AD provider: true)
209 The IPA provider will set to option to 'true' if it detects that
211 the server is capable of handling enterprise principals and the
212 option is not set explicitly in the config file.
213 krb5_use_subdomain_realm (boolean)
215 Specifies to use subdomains realms for the authentication of users
216 from trusted domains. This option can be set to 'true' if
217 enterprise principals are used with upnSuffixes which are not known
218 on the parent domain KDCs. If the option is set to 'true' SSSD will
219 try to send the request directly to a KDC of the trusted domain the
220 user is coming from.
221 Default: false
223 krb5_map_user (string)
225 The list of mappings is given as a comma-separated list of pairs
226 “username:primary” where “username” is a UNIX user name and
227 “primary” is a user part of a kerberos principal. This mapping is
228 used when user is authenticating using “auth_provider = krb5”.
229 example:
231 krb5_realm = REALM
233 krb5_map_user = joe:juser,dick:richard
234 “joe” and “dick” are UNIX user names and “juser” and “richard” are
236 primaries of kerberos principals. For user “joe” resp. “dick” SSSD
237 will try to kinit as “juser@REALM” resp. “richard@REALM”.
238 Default: not set
240 krb5_auth_timeout (integer)
242 Timeout in seconds after an online authentication request or change
243 password request is aborted. If possible, the authentication
244 request is continued offline.
245 Default: 6
247 krb5_validate (boolean)
249 Verify with the help of krb5_keytab that the TGT obtained has not
250 been spoofed. The keytab is checked for entries sequentially, and
251 the first entry with a matching realm is used for validation. If no
252 entry matches the realm, the last entry in the keytab is used. This
253 process can be used to validate environments using cross-realm
254 trust by placing the appropriate keytab entry as the last entry or
255 the only entry in the keytab file.
256 Default: false
258 krb5_renewable_lifetime (string)
260 Request a renewable ticket with a total lifetime, given as an
261 integer immediately followed by a time unit:
262 s for seconds
264 m for minutes
266 h for hours
268 d for days.
270 If there is no unit given, s is assumed.
272 NOTE: It is not possible to mix units. To set the renewable
274 lifetime to one and a half hours, use '90m' instead of '1h30m'.
275 Default: not set, i.e. the TGT is not renewable
277 krb5_lifetime (string)
279 Request ticket with a lifetime, given as an integer immediately
280 followed by a time unit:
281 s for seconds
283 m for minutes
285 h for hours
287 d for days.
289 If there is no unit given s is assumed.
291 NOTE: It is not possible to mix units. To set the lifetime to one
293 and a half hours please use '90m' instead of '1h30m'.
294 Default: not set, i.e. the default ticket lifetime configured on
296 the KDC.
297 krb5_renew_interval (string)
299 The time in seconds between two checks if the TGT should be
300 renewed. TGTs are renewed if about half of their lifetime is
301 exceeded, given as an integer immediately followed by a time unit:
302 s for seconds
304 m for minutes
306 h for hours
308 d for days.
310 If there is no unit given, s is assumed.
312 NOTE: It is not possible to mix units. To set the renewable
314 lifetime to one and a half hours, use '90m' instead of '1h30m'.
315 If this option is not set or is 0 the automatic renewal is
317 disabled.
318 Default: not set
320 krb5_canonicalize (boolean)
322 Specifies if the host and user principal should be canonicalized.
323 This feature is available with MIT Kerberos 1.7 and later versions.
324 Default: false
326
328 The failover feature allows back ends to automatically switch to a
329 different server if the current server fails.
330 Failover Syntax
332 The list of servers is given as a comma-separated list; any number of
333 spaces is allowed around the comma. The servers are listed in order of
334 preference. The list can contain any number of servers.
335 For each failover-enabled config option, two variants exist: primary
337 and backup. The idea is that servers in the primary list are preferred
338 and backup servers are only searched if no primary servers can be
339 reached. If a backup server is selected, a timeout of 31 seconds is
340 set. After this timeout SSSD will periodically try to reconnect to one
341 of the primary servers. If it succeeds, it will replace the current
342 active (backup) server.
343 The Failover Mechanism
345 The failover mechanism distinguishes between a machine and a service.
346 The back end first tries to resolve the hostname of a given machine; if
347 this resolution attempt fails, the machine is considered offline. No
348 further attempts are made to connect to this machine for any other
349 service. If the resolution attempt succeeds, the back end tries to
350 connect to a service on this machine. If the service connection attempt
351 fails, then only this particular service is considered offline and the
352 back end automatically switches over to the next service. The machine
353 is still considered online and might still be tried for another
354 service.
355 Further connection attempts are made to machines or services marked as
357 offline after a specified period of time; this is currently hard coded
358 to 30 seconds.
359 If there are no more machines to try, the back end as a whole switches
361 to offline mode, and then attempts to reconnect every 30 seconds.
362 Failover time outs and tuning
364 Resolving a server to connect to can be as simple as running a single
365 DNS query or can involve several steps, such as finding the correct
366 site or trying out multiple host names in case some of the configured
367 servers are not reachable. The more complex scenarios can take some
368 time and SSSD needs to balance between providing enough time to finish
369 the resolution process but on the other hand, not trying for too long
370 before falling back to offline mode. If the SSSD debug logs show that
371 the server resolution is timing out before a live server is contacted,
372 you can consider changing the time outs.
373 This section lists the available tunables. Please refer to their
375 description in the sssd.conf(5), manual page.
376 dns_resolver_server_timeout
378 Time in milliseconds that sets how long would SSSD talk to a single
379 DNS server before trying next one.
380 Default: 1000
382 dns_resolver_op_timeout
384 Time in seconds to tell how long would SSSD try to resolve single
385 DNS query (e.g. resolution of a hostname or an SRV record) before
386 trying the next hostname or discovery domain.
387 Default: 3
389 dns_resolver_timeout
391 How long would SSSD try to resolve a failover service. This service
392 resolution internally might include several steps, such as
393 resolving DNS SRV queries or locating the site.
394 Default: 6
396 For LDAP-based providers, the resolve operation is performed as part of
398 an LDAP connection operation. Therefore, also the “ldap_opt_timeout”
399 timeout should be set to a larger value than “dns_resolver_timeout”
400 which in turn should be set to a larger value than
401 “dns_resolver_op_timeout” which should be larger than
402 “dns_resolver_server_timeout”.
403
405 The service discovery feature allows back ends to automatically find
406 the appropriate servers to connect to using a special DNS query. This
407 feature is not supported for backup servers.
408 Configuration
410 If no servers are specified, the back end automatically uses service
411 discovery to try to find a server. Optionally, the user may choose to
412 use both fixed server addresses and service discovery by inserting a
413 special keyword, “_srv_”, in the list of servers. The order of
414 preference is maintained. This feature is useful if, for example, the
415 user prefers to use service discovery whenever possible, and fall back
416 to a specific server when no servers can be discovered using DNS.
417 The domain name
419 Please refer to the “dns_discovery_domain” parameter in the
420 sssd.conf(5) manual page for more details.
421 The protocol
423 The queries usually specify _tcp as the protocol. Exceptions are
424 documented in respective option description.
425 See Also
427 For more information on the service discovery mechanism, refer to RFC
428 2782.
429
431 The following example assumes that SSSD is correctly configured and FOO
432 is one of the domains in the [sssd] section. This example shows only
433 configuration of Kerberos authentication; it does not include any
434 identity provider.
435 [domain/FOO]
437 auth_provider = krb5
438 krb5_server = 192.168.1.1
439 krb5_realm = EXAMPLE.COM
440
443 sssd(8), sssd.conf(5), sssd-ldap(5), sssd-krb5(5), sssd-simple(5),
444 sssd-ipa(5), sssd-ad(5), sssd-files(5), sssd-sudo(5), sssd-session-
445 recording(5), sss_cache(8), sss_debuglevel(8), sss_obfuscate(8),
446 sss_seed(8), sssd_krb5_locator_plugin(8), sss_ssh_authorizedkeys(8),
447 sss_ssh_knownhostsproxy(8), sssd-ifp(5), pam_sss(8). sss_rpcidmapd(5)
448 sssd-systemtap(5)
449
451 The SSSD upstream - https://github.com/SSSD/sssd/
452SSSD 07/04/2022 SSSD-KRB5(5)