1SSSD-KRB5(5) File Formats and Conventions SSSD-KRB5(5)
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6 sssd-krb5 - SSSD Kerberos provider
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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.
25 Please note that an empty .k5login file will deny all access to this
26 user. To activate this feature, use 'access_provider = krb5' in your
27 SSSD 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_auth_timeout (integer)
130 Timeout in seconds after an online authentication request or change
131 password request is aborted. If possible, the authentication
132 request is continued offline.
133 Default: 6
135 krb5_validate (boolean)
137 Verify with the help of krb5_keytab that the TGT obtained has not
138 been spoofed. The keytab is checked for entries sequentially, and
139 the first entry with a matching realm is used for validation. If no
140 entry matches the realm, the last entry in the keytab is used. This
141 process can be used to validate environments using cross-realm
142 trust by placing the appropriate keytab entry as the last entry or
143 the only entry in the keytab file.
144 Default: false
146 krb5_keytab (string)
148 The location of the keytab to use when validating credentials
149 obtained from KDCs.
150 Default: /etc/krb5.keytab
152 krb5_store_password_if_offline (boolean)
154 Store the password of the user if the provider is offline and use
155 it to request a TGT when the provider comes online again.
156 NOTE: this feature is only available on Linux. Passwords stored in
158 this way are kept in plaintext in the kernel keyring and are
159 potentially accessible by the root user (with difficulty).
160 Default: false
162 krb5_renewable_lifetime (string)
164 Request a renewable ticket with a total lifetime, given as an
165 integer immediately followed by a time unit:
166 s for seconds
168 m for minutes
170 h for hours
172 d for days.
174 If there is no unit given, s is assumed.
176 NOTE: It is not possible to mix units. To set the renewable
178 lifetime to one and a half hours, use '90m' instead of '1h30m'.
179 Default: not set, i.e. the TGT is not renewable
181 krb5_lifetime (string)
183 Request ticket with a lifetime, given as an integer immediately
184 followed by a time unit:
185 s for seconds
187 m for minutes
189 h for hours
191 d for days.
193 If there is no unit given s is assumed.
195 NOTE: It is not possible to mix units. To set the lifetime to one
197 and a half hours please use '90m' instead of '1h30m'.
198 Default: not set, i.e. the default ticket lifetime configured on
200 the KDC.
201 krb5_renew_interval (string)
203 The time in seconds between two checks if the TGT should be
204 renewed. TGTs are renewed if about half of their lifetime is
205 exceeded, given as an integer immediately followed by a time unit:
206 s for seconds
208 m for minutes
210 h for hours
212 d for days.
214 If there is no unit given, s is assumed.
216 NOTE: It is not possible to mix units. To set the renewable
218 lifetime to one and a half hours, use '90m' instead of '1h30m'.
219 If this option is not set or is 0 the automatic renewal is
221 disabled.
222 Default: not set
224 krb5_use_fast (string)
226 Enables flexible authentication secure tunneling (FAST) for
227 Kerberos pre-authentication. The following options are supported:
228 never use FAST. This is equivalent to not setting this option at
230 all.
231 try to use FAST. If the server does not support FAST, continue the
233 authentication without it.
234 demand to use FAST. The authentication fails if the server does not
236 require fast.
237 Default: not set, i.e. FAST is not used.
239 NOTE: a keytab is required to use FAST.
241 NOTE: SSSD supports FAST only with MIT Kerberos version 1.8 and
243 later. If SSSD is used with an older version of MIT Kerberos, using
244 this option is a configuration error.
245 krb5_fast_principal (string)
247 Specifies the server principal to use for FAST.
248 krb5_canonicalize (boolean)
250 Specifies if the host and user principal should be canonicalized.
251 This feature is available with MIT Kerberos 1.7 and later versions.
252 Default: false
254 krb5_use_kdcinfo (boolean)
256 Specifies if the SSSD should instruct the Kerberos libraries what
257 realm and which KDCs to use. This option is on by default, if you
258 disable it, you need to configure the Kerberos library using the
259 krb5.conf(5) configuration file.
260 See the sssd_krb5_locator_plugin(8) manual page for more
262 information on the locator plugin.
263 Default: true
265 krb5_kdcinfo_lookahead (string)
267 When krb5_use_kdcinfo is set to true, you can limit the amount of
268 servers handed to sssd_krb5_locator_plugin(8). This might be
269 helpful when there are too many servers discovered using SRV
270 record.
271 The krb5_kdcinfo_lookahead option contains two numbers separated by
273 a colon. The first number represents number of primary servers used
274 and the second number specifies the number of backup servers.
275 For example 10:0 means that up to 10 primary servers will be handed
277 to sssd_krb5_locator_plugin(8) but no backup servers.
278 Default: 3:1
280 krb5_use_enterprise_principal (boolean)
282 Specifies if the user principal should be treated as enterprise
283 principal. See section 5 of RFC 6806 for more details about
284 enterprise principals.
285 Default: false (AD provider: true)
287 The IPA provider will set to option to 'true' if it detects that
289 the server is capable of handling enterprise principals and the
290 option is not set explicitly in the config file.
291 krb5_map_user (string)
293 The list of mappings is given as a comma-separated list of pairs
294 “username:primary” where “username” is a UNIX user name and
295 “primary” is a user part of a kerberos principal. This mapping is
296 used when user is authenticating using “auth_provider = krb5”.
297 example:
299 krb5_realm = REALM
301 krb5_map_user = joe:juser,dick:richard
302 “joe” and “dick” are UNIX user names and “juser” and “richard” are
304 primaries of kerberos principals. For user “joe” resp. “dick” SSSD
305 will try to kinit as “juser@REALM” resp. “richard@REALM”.
306 Default: not set
308
310 The failover feature allows back ends to automatically switch to a
311 different server if the current server fails.
312 Failover Syntax
314 The list of servers is given as a comma-separated list; any number of
315 spaces is allowed around the comma. The servers are listed in order of
316 preference. The list can contain any number of servers.
317 For each failover-enabled config option, two variants exist: primary
319 and backup. The idea is that servers in the primary list are preferred
320 and backup servers are only searched if no primary servers can be
321 reached. If a backup server is selected, a timeout of 31 seconds is
322 set. After this timeout SSSD will periodically try to reconnect to one
323 of the primary servers. If it succeeds, it will replace the current
324 active (backup) server.
325 The Failover Mechanism
327 The failover mechanism distinguishes between a machine and a service.
328 The back end first tries to resolve the hostname of a given machine; if
329 this resolution attempt fails, the machine is considered offline. No
330 further attempts are made to connect to this machine for any other
331 service. If the resolution attempt succeeds, the back end tries to
332 connect to a service on this machine. If the service connection attempt
333 fails, then only this particular service is considered offline and the
334 back end automatically switches over to the next service. The machine
335 is still considered online and might still be tried for another
336 service.
337 Further connection attempts are made to machines or services marked as
339 offline after a specified period of time; this is currently hard coded
340 to 30 seconds.
341 If there are no more machines to try, the back end as a whole switches
343 to offline mode, and then attempts to reconnect every 30 seconds.
344 Failover time outs and tuning
346 Resolving a server to connect to can be as simple as running a single
347 DNS query or can involve several steps, such as finding the correct
348 site or trying out multiple host names in case some of the configured
349 servers are not reachable. The more complex scenarios can take some
350 time and SSSD needs to balance between providing enough time to finish
351 the resolution process but on the other hand, not trying for too long
352 before falling back to offline mode. If the SSSD debug logs show that
353 the server resolution is timing out before a live server is contacted,
354 you can consider changing the time outs.
355 This section lists the available tunables. Please refer to their
357 description in the sssd.conf(5), manual page.
358 dns_resolver_server_timeout
360 Time in milliseconds that sets how long would SSSD talk to a single
361 DNS server before trying next one.
362 Default: 1000
364 dns_resolver_op_timeout
366 Time in seconds to tell how long would SSSD try to resolve single
367 DNS query (e.g. resolution of a hostname or an SRV record) before
368 trying the next hostname or discovery domain.
369 Default: 2
371 dns_resolver_timeout
373 How long would SSSD try to resolve a failover service. This service
374 resolution internally might include several steps, such as
375 resolving DNS SRV queries or locating the site.
376 Default: 4
378 For LDAP-based providers, the resolve operation is performed as part of
380 an LDAP connection operation. Therefore, also the “ldap_opt_timeout>”
381 timeout should be set to a larger value than “dns_resolver_timeout”
382 which in turn should be set to a larger value than
383 “dns_resolver_op_timeout” which should be larger than
384 “dns_resolver_server_timeout”.
385
387 The service discovery feature allows back ends to automatically find
388 the appropriate servers to connect to using a special DNS query. This
389 feature is not supported for backup servers.
390 Configuration
392 If no servers are specified, the back end automatically uses service
393 discovery to try to find a server. Optionally, the user may choose to
394 use both fixed server addresses and service discovery by inserting a
395 special keyword, “_srv_”, in the list of servers. The order of
396 preference is maintained. This feature is useful if, for example, the
397 user prefers to use service discovery whenever possible, and fall back
398 to a specific server when no servers can be discovered using DNS.
399 The domain name
401 Please refer to the “dns_discovery_domain” parameter in the
402 sssd.conf(5) manual page for more details.
403 The protocol
405 The queries usually specify _tcp as the protocol. Exceptions are
406 documented in respective option description.
407 See Also
409 For more information on the service discovery mechanism, refer to RFC
410 2782.
411
413 The following example assumes that SSSD is correctly configured and FOO
414 is one of the domains in the [sssd] section. This example shows only
415 configuration of Kerberos authentication; it does not include any
416 identity provider.
417 [domain/FOO]
419 auth_provider = krb5
420 krb5_server = 192.168.1.1
421 krb5_realm = EXAMPLE.COM
422
425 sssd(8), sssd.conf(5), sssd-ldap(5), sssd-krb5(5), sssd-simple(5),
426 sssd-ipa(5), sssd-ad(5), sssd-files(5), sssd-sudo(5), sssd-session-
427 recording(5), sss_cache(8), sss_debuglevel(8), sss_obfuscate(8),
428 sss_seed(8), sssd_krb5_locator_plugin(8), sss_ssh_authorizedkeys(8),
429 sss_ssh_knownhostsproxy(8), sssd-ifp(5), pam_sss(8). sss_rpcidmapd(5)
430 sssd-systemtap(5)
431
433 The SSSD upstream - https://pagure.io/SSSD/sssd/
434SSSD 10/22/2019 SSSD-KRB5(5)