| SSSD-LDAP(5) | File Formats and Conventions | SSSD-LDAP(5) |
NAME¶
sssd-ldap - SSSD LDAP provider
DESCRIPTION¶
This manual page describes the configuration of LDAP domains for sssd(8). Refer to the “FILE FORMAT” section of the sssd.conf(5) manual page for detailed syntax information.
You can configure SSSD to use more than one LDAP domain.
LDAP back end supports id, auth, access and chpass providers. If you want to authenticate against an LDAP server either TLS/SSL or LDAPS is required. sssd does not support authentication over an unencrypted channel. Even if the LDAP server is used only as an identity provider, an encrypted channel is strongly recommended. Please refer to “ldap_access_filter” config option for more information about using LDAP as an access provider.
CONFIGURATION OPTIONS¶
All of the common configuration options that apply to SSSD domains also apply to LDAP domains. Refer to the “DOMAIN SECTIONS” section of the sssd.conf(5) manual page for full details. Note that SSSD LDAP mapping attributes are described in the sssd-ldap-attributes(5) manual page.
ldap_uri, ldap_backup_uri (string)
The format of the URI must match the format defined in RFC 2732:
ldap[s]://<host>[:port]
For explicit IPv6 addresses, <host> must be enclosed in brackets []
example: ldap://[fc00::126:25]:389
ldap_chpass_uri, ldap_chpass_backup_uri (string)
To enable service discovery ldap_chpass_dns_service_name must be set.
Default: empty, i.e. ldap_uri is used.
ldap_search_base (string)
Starting with SSSD 1.7.0, SSSD supports multiple search bases using the syntax:
search_base[?scope?[filter][?search_base?scope?[filter]]*]
The scope can be one of "base", "onelevel" or "subtree".
The filter must be a valid LDAP search filter as specified by http://www.ietf.org/rfc/rfc2254.txt
Examples:
ldap_search_base = dc=example,dc=com (which is equivalent to) ldap_search_base = dc=example,dc=com?subtree?
ldap_search_base = cn=host_specific,dc=example,dc=com?subtree?(host=thishost)?dc=example.com?subtree?
Note: It is unsupported to have multiple search bases which reference identically-named objects (for example, groups with the same name in two different search bases). This will lead to unpredictable behavior on client machines.
Default: If not set, the value of the defaultNamingContext or namingContexts attribute from the RootDSE of the LDAP server is used. If defaultNamingContext does not exist or has an empty value namingContexts is used. The namingContexts attribute must have a single value with the DN of the search base of the LDAP server to make this work. Multiple values are are not supported.
ldap_schema (string)
Four schema types are currently supported:
The main difference between these schema types is how group memberships are recorded in the server. With rfc2307, group members are listed by name in the memberUid attribute. With rfc2307bis and IPA, group members are listed by DN and stored in the member attribute. The AD schema type sets the attributes to correspond with Active Directory 2008r2 values.
Default: rfc2307
ldap_pwmodify_mode (string)
Two modes are currently supported:
Note: First, a new connection is established to verify current password by binding as the user that requested password change. If successful, this connection is used to change the password therefore the user must have write access to userPassword attribute.
Default: exop
ldap_default_bind_dn (string)
ldap_default_authtok_type (string)
The two mechanisms currently supported are:
password
obfuscated_password
Default: password
See the sss_obfuscate(8) manual page for more information.
ldap_default_authtok (string)
ldap_force_upper_case_realm (boolean)
Default: false
ldap_enumeration_refresh_timeout (integer)
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 300
ldap_purge_cache_timeout (integer)
Setting this option to zero will disable the cache cleanup operation. Please note that if enumeration is enabled, the cleanup task is required in order to detect entries removed from the server and can't be disabled. By default, the cleanup task will run every 3 hours with enumeration enabled.
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 0 (disabled)
ldap_group_nesting_level (integer)
Note: This option specifies the guaranteed level of nested groups to be processed for any lookup. However, nested groups beyond this limit may be returned if previous lookups already resolved the deeper nesting levels. Also, subsequent lookups for other groups may enlarge the result set for original lookup if re-queried.
If ldap_group_nesting_level is set to 0 then no nested groups are processed at all. However, when connected to Active-Directory Server 2008 and later using “id_provider=ad” it is furthermore required to disable usage of Token-Groups by setting ldap_use_tokengroups to false in order to restrict group nesting.
Default: 2
ldap_use_tokengroups
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: True for AD and IPA otherwise False.
ldap_host_search_base (string)
See “ldap_search_base” for information about configuring multiple search bases.
Default: the value of ldap_search_base
ldap_service_search_base (string)
syntax:
search_base[?scope?[filter][?search_base?scope?[filter]]*]
The scope can be one of "base", "onelevel" or "subtree". The scope functions as specified in section 4.5.1.2 of http://tools.ietf.org/html/rfc4511
The filter must be a valid LDAP search filter as specified by http://www.ietf.org/rfc/rfc2254.txt
For examples of this syntax, please refer to the “ldap_search_base” examples section.
Default: the value of ldap_search_base
Please note that specifying scope or filter is not supported for searches against an Active Directory Server that might yield a large number of results and trigger the Range Retrieval extension in the response.
ldap_iphost_search_base (string)
syntax:
search_base[?scope?[filter][?search_base?scope?[filter]]*]
The scope can be one of "base", "onelevel" or "subtree". The scope functions as specified in section 4.5.1.2 of http://tools.ietf.org/html/rfc4511
The filter must be a valid LDAP search filter as specified by http://www.ietf.org/rfc/rfc2254.txt
For examples of this syntax, please refer to the “ldap_search_base” examples section.
Default: the value of ldap_search_base
Please note that specifying scope or filter is not supported for searches against an Active Directory Server that might yield a large number of results and trigger the Range Retrieval extension in the response.
ldap_ipnetwork_search_base (string)
syntax:
search_base[?scope?[filter][?search_base?scope?[filter]]*]
The scope can be one of "base", "onelevel" or "subtree". The scope functions as specified in section 4.5.1.2 of http://tools.ietf.org/html/rfc4511
The filter must be a valid LDAP search filter as specified by http://www.ietf.org/rfc/rfc2254.txt
For examples of this syntax, please refer to the “ldap_search_base” examples section.
Default: the value of ldap_search_base
Please note that specifying scope or filter is not supported for searches against an Active Directory Server that might yield a large number of results and trigger the Range Retrieval extension in the response.
ldap_search_timeout (integer)
Note: this option is subject to change in future versions of the SSSD. It will likely be replaced at some point by a series of timeouts for specific lookup types.
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 6
ldap_enumeration_search_timeout (integer)
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 60
ldap_network_timeout (integer)
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 6
ldap_opt_timeout (integer)
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 8
ldap_connection_expire_timeout (integer)
If the connection is idle (not actively running an operation) within ldap_opt_timeout seconds of expiration, then it will be closed early to ensure that a new query cannot require the connection to remain open past its expiration. This implies that connections will always be closed immediately and will never be reused if ldap_connection_expire_timeout <= ldap_opt_timout
This timeout can be extended of a random value specified by ldap_connection_expire_offset
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 900 (15 minutes)
ldap_connection_expire_offset (integer)
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 0
ldap_connection_idle_timeout (integer)
You can disable this timeout by setting the value to 0.
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 900 (15 minutes)
ldap_page_size (integer)
Default: 1000
ldap_disable_paging (boolean)
Example: OpenLDAP servers with the paging control module installed on the server but not enabled will report it in the RootDSE but be unable to use it.
Example: 389 DS has a bug where it can only support a one paging control at a time on a single connection. On busy clients, this can result in some requests being denied.
Default: False
ldap_disable_range_retrieval (boolean)
Active Directory limits the number of members to be retrieved in a single lookup using the MaxValRange policy (which defaults to 1500 members). If a group contains more members, the reply would include an AD-specific range extension. This option disables parsing of the range extension, therefore large groups will appear as having no members.
Default: False
ldap_sasl_minssf (integer)
Default: Use the system default (usually specified by ldap.conf)
ldap_sasl_maxssf (integer)
Default: Use the system default (usually specified by ldap.conf)
ldap_deref_threshold (integer)
You can turn off dereference lookups completely by setting the value to 0. Please note that there are some codepaths in SSSD, like the IPA HBAC provider, that are only implemented using the dereference call, so even with dereference explicitly disabled, those parts will still use dereference if the server supports it and advertises the dereference control in the rootDSE object.
A dereference lookup is a means of fetching all group members in a single LDAP call. Different LDAP servers may implement different dereference methods. The currently supported servers are 389/RHDS, OpenLDAP and Active Directory.
Note: If any of the search bases specifies a search filter, then the dereference lookup performance enhancement will be disabled regardless of this setting.
Default: 10
ldap_ignore_unreadable_references (bool)
This parameter may be useful when using the AD provider and the computer account that sssd uses to connect to AD does not have access to a particular entry or LDAP sub-tree for security reasons.
Default: False
ldap_tls_reqcert (string)
never = The client will not request or check any server certificate.
allow = The server certificate is requested. If no certificate is provided, the session proceeds normally. If a bad certificate is provided, it will be ignored and the session proceeds normally.
try = The server certificate is requested. If no certificate is provided, the session proceeds normally. If a bad certificate is provided, the session is immediately terminated.
demand = The server certificate is requested. If no certificate is provided, or a bad certificate is provided, the session is immediately terminated.
hard = Same as “demand”
Default: hard
ldap_tls_cacert (string)
Default: use OpenLDAP defaults, typically in /etc/openldap/ldap.conf
ldap_tls_cacertdir (string)
Default: use OpenLDAP defaults, typically in /etc/openldap/ldap.conf
ldap_tls_cert (string)
Default: not set
ldap_tls_key (string)
Default: not set
ldap_tls_cipher_suite (string)
Default: use OpenLDAP defaults, typically in /etc/openldap/ldap.conf
ldap_id_use_start_tls (boolean)
Default: false
ldap_id_mapping (boolean)
Currently this feature supports only ActiveDirectory objectSID mapping.
Default: false
ldap_min_id, ldap_max_id (integer)
Default: not set (both options are set to 0)
ldap_sasl_mech (string)
If the backend supports sub-domains the value of ldap_sasl_mech is automatically inherited to the sub-domains. If a different value is needed for a sub-domain it can be overwritten by setting ldap_sasl_mech for this sub-domain explicitly. Please see TRUSTED DOMAIN SECTION in sssd.conf(5) for details.
Default: not set
ldap_sasl_authid (string)
hostname@REALM netbiosname$@REALM host/hostname@REALM *$@REALM host/*@REALM host/*
If none of them are found, the first principal in keytab is returned.
Default: host/hostname@REALM
ldap_sasl_realm (string)
Default: the value of krb5_realm.
ldap_sasl_canonicalize (boolean)
Default: false;
ldap_krb5_keytab (string)
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: System keytab, normally /etc/krb5.keytab
ldap_krb5_init_creds (boolean)
Default: true
ldap_krb5_ticket_lifetime (integer)
This option can be also set per subdomain or inherited via subdomain_inherit.
Default: 86400 (24 hours)
krb5_server, krb5_backup_server (string)
When using service discovery for KDC or kpasswd servers, SSSD first searches for DNS entries that specify _udp as the protocol and falls back to _tcp if none are found.
This option was named “krb5_kdcip” in earlier releases of SSSD. While the legacy name is recognized for the time being, users are advised to migrate their config files to use “krb5_server” instead.
krb5_realm (string)
Default: System defaults, see /etc/krb5.conf
krb5_canonicalize (boolean)
Default: false
krb5_use_kdcinfo (boolean)
See the sssd_krb5_locator_plugin(8) manual page for more information on the locator plugin.
Default: true
ldap_pwd_policy (string)
none - No evaluation on the client side. This option cannot disable server-side password policies.
shadow - Use shadow(5) style attributes to evaluate if the password has expired. Please see option "ldap_chpass_update_last_change" as well.
mit_kerberos - Use the attributes used by MIT Kerberos to determine if the password has expired. Use chpass_provider=krb5 to update these attributes when the password is changed.
Default: none
Note: if a password policy is configured on server side, it always takes precedence over policy set with this option.
ldap_referrals (boolean)
Please note that sssd only supports referral chasing when it is compiled with OpenLDAP version 2.4.13 or higher.
Chasing referrals may incur a performance penalty in environments that use them heavily, a notable example is Microsoft Active Directory. If your setup does not in fact require the use of referrals, setting this option to false might bring a noticeable performance improvement. Setting this option to false is therefore recommended in case the SSSD LDAP provider is used together with Microsoft Active Directory as a backend. Even if SSSD would be able to follow the referral to a different AD DC no additional data would be available.
Default: true
ldap_dns_service_name (string)
Default: ldap
ldap_chpass_dns_service_name (string)
Default: not set, i.e. service discovery is disabled
ldap_chpass_update_last_change (bool)
It is recommend to set this option explicitly if "ldap_pwd_policy = shadow" is used to let SSSD know if the LDAP server will update shadowLastChange LDAP attribute automatically after a password change or if SSSD has to update it.
Default: False
ldap_access_filter (string)
Example:
access_provider = ldap ldap_access_filter = (employeeType=admin)
This example means that access to this host is restricted to users whose employeeType attribute is set to "admin".
Offline caching for this feature is limited to determining whether the user's last online login was granted access permission. If they were granted access during their last login, they will continue to be granted access while offline and vice versa.
Default: Empty
ldap_account_expire_policy (string)
Please note that it is always recommended to use server side access control, i.e. the LDAP server should deny the bind request with a suitable error code even if the password is correct.
The following values are allowed:
shadow: use the value of ldap_user_shadow_expire to determine if the account is expired.
ad: use the value of the 32bit field ldap_user_ad_user_account_control and allow access if the second bit is not set. If the attribute is missing access is granted. Also the expiration time of the account is checked.
rhds, ipa, 389ds: use the value of ldap_ns_account_lock to check if access is allowed or not.
nds: the values of ldap_user_nds_login_allowed_time_map, ldap_user_nds_login_disabled and ldap_user_nds_login_expiration_time are used to check if access is allowed. If both attributes are missing access is granted.
Please note that the ldap_access_order configuration option must include “expire” in order for the ldap_account_expire_policy option to work.
Default: Empty
ldap_access_order (string)
filter: use ldap_access_filter
lockout: use account locking. If set, this option denies access in case that ldap attribute 'pwdAccountLockedTime' is present and has value of '000001010000Z'. Please see the option ldap_pwdlockout_dn. Please note that 'access_provider = ldap' must be set for this feature to work.
Please note that this option is superseded by the “ppolicy” option and might be removed in a future release.
ppolicy: use account locking. If set, this option denies access in case that ldap attribute 'pwdAccountLockedTime' is present and has value of '000001010000Z' or represents any time in the past. The value of the 'pwdAccountLockedTime' attribute must end with 'Z', which denotes the UTC time zone. Other time zones are not currently supported and will result in "access-denied" when users attempt to log in. Please see the option ldap_pwdlockout_dn. Please note that 'access_provider = ldap' must be set for this feature to work.
expire: use ldap_account_expire_policy
pwd_expire_policy_reject, pwd_expire_policy_warn, pwd_expire_policy_renew: These options are useful if users are interested in being warned that password is about to expire and authentication is based on using a different method than passwords - for example SSH keys.
The difference between these options is the action taken if user password is expired:
Please note that 'access_provider = ldap' must be set for this feature to work. Also 'ldap_pwd_policy' must be set to an appropriate password policy.
authorized_service: use the authorizedService attribute to determine access
host: use the host attribute to determine access
rhost: use the rhost attribute to determine whether remote host can access
Please note, rhost field in pam is set by application, it is better to check what the application sends to pam, before enabling this access control option
Default: filter
Please note that it is a configuration error if a value is used more than once.
ldap_pwdlockout_dn (string)
Example: cn=ppolicy,ou=policies,dc=example,dc=com
Default: cn=ppolicy,ou=policies,$ldap_search_base
ldap_deref (string)
never: Aliases are never dereferenced.
searching: Aliases are dereferenced in subordinates of the base object, but not in locating the base object of the search.
finding: Aliases are only dereferenced when locating the base object of the search.
always: Aliases are dereferenced both in searching and in locating the base object of the search.
Default: Empty (this is handled as never by the LDAP client libraries)
ldap_rfc2307_fallback_to_local_users (boolean)
In some environments where the RFC2307 schema is used, local users are made members of LDAP groups by adding their names to the memberUid attribute. The self-consistency of the domain is compromised when this is done, so SSSD would normally remove the "missing" users from the cached group memberships as soon as nsswitch tries to fetch information about the user via getpw*() or initgroups() calls.
This option falls back to checking if local users are referenced, and caches them so that later initgroups() calls will augment the local users with the additional LDAP groups.
Default: false
wildcard_limit (integer)
At the moment, only the InfoPipe responder supports wildcard lookups.
Default: 1000 (often the size of one page)
ldap_library_debug_level (integer)
OpenLDAP uses a bitmap to enable debugging for specific components, -1 will enable full debug output.
Default: 0 (libldap debugging disabled)
SUDO OPTIONS¶
The detailed instructions for configuration of sudo_provider are in the manual page sssd-sudo(5).
ldap_sudo_full_refresh_interval (integer)
The value must be greater than ldap_sudo_smart_refresh_interval
You can disable full refresh by setting this option to 0. However, either smart or full refresh must be enabled.
Default: 21600 (6 hours)
ldap_sudo_smart_refresh_interval (integer)
If USN attributes are not supported by the server, the modifyTimestamp attribute is used instead.
Note: the highest USN value can be updated by three tasks: 1) By sudo full and smart refresh (if updated rules are found), 2) by enumeration of users and groups (if enabled and updated users or groups are found) and 3) by reconnecting to the server (by default every 15 minutes, see ldap_connection_expire_timeout).
You can disable smart refresh by setting this option to 0. However, either smart or full refresh must be enabled.
Default: 900 (15 minutes)
ldap_sudo_random_offset (integer)
Note that this random offset is also applied on the first SSSD start which delays the first sudo rules refresh. This prolongs the time when the sudo rules are not available for use.
You can disable this offset by setting the value to 0.
Default: 0 (disabled)
ldap_sudo_use_host_filter (boolean)
Default: true
ldap_sudo_hostnames (string)
If this option is empty, SSSD will try to discover the hostname and the fully qualified domain name automatically.
If ldap_sudo_use_host_filter is false then this option has no effect.
Default: not specified
ldap_sudo_ip (string)
If this option is empty, SSSD will try to discover the addresses automatically.
If ldap_sudo_use_host_filter is false then this option has no effect.
Default: not specified
ldap_sudo_include_netgroups (boolean)
If ldap_sudo_use_host_filter is false then this option has no effect.
Default: true
ldap_sudo_include_regexp (boolean)
If ldap_sudo_use_host_filter is false then this option has no effect.
Note
Using wildcard is an operation that is very costly to evaluate on the LDAP server side!
This manual page only describes attribute name mapping. For detailed explanation of sudo related attribute semantics, see sudoers.ldap(5)
AUTOFS OPTIONS¶
Some of the defaults for the parameters below are dependent on the LDAP schema.
ldap_autofs_map_master_name (string)
Default: auto.master
ldap_autofs_map_object_class (string)
Default: nisMap (rfc2307, autofs_provider=ad), otherwise automountMap
ldap_autofs_map_name (string)
Default: nisMapName (rfc2307, autofs_provider=ad), otherwise automountMapName
ldap_autofs_entry_object_class (string)
Default: nisObject (rfc2307, autofs_provider=ad), otherwise automount
ldap_autofs_entry_key (string)
Default: cn (rfc2307, autofs_provider=ad), otherwise automountKey
ldap_autofs_entry_value (string)
Default: nisMapEntry (rfc2307, autofs_provider=ad), otherwise automountInformation
Please note that the automounter only reads the master map on startup, so if any autofs-related changes are made to the sssd.conf, you typically also need to restart the automounter daemon after restarting the SSSD.
ADVANCED OPTIONS¶
These options are supported by LDAP domains, but they should be used with caution. Please include them in your configuration only if you know what you are doing.
ldap_netgroup_search_base (string)
syntax:
search_base[?scope?[filter][?search_base?scope?[filter]]*]
The scope can be one of "base", "onelevel" or "subtree". The scope functions as specified in section 4.5.1.2 of http://tools.ietf.org/html/rfc4511
The filter must be a valid LDAP search filter as specified by http://www.ietf.org/rfc/rfc2254.txt
For examples of this syntax, please refer to the “ldap_search_base” examples section.
Default: the value of ldap_search_base
Please note that specifying scope or filter is not supported for searches against an Active Directory Server that might yield a large number of results and trigger the Range Retrieval extension in the response.
ldap_user_search_base (string)
syntax:
search_base[?scope?[filter][?search_base?scope?[filter]]*]
The scope can be one of "base", "onelevel" or "subtree". The scope functions as specified in section 4.5.1.2 of http://tools.ietf.org/html/rfc4511
The filter must be a valid LDAP search filter as specified by http://www.ietf.org/rfc/rfc2254.txt
For examples of this syntax, please refer to the “ldap_search_base” examples section.
Default: the value of ldap_search_base
Please note that specifying scope or filter is not supported for searches against an Active Directory Server that might yield a large number of results and trigger the Range Retrieval extension in the response.
ldap_group_search_base (string)
syntax:
search_base[?scope?[filter][?search_base?scope?[filter]]*]
The scope can be one of "base", "onelevel" or "subtree". The scope functions as specified in section 4.5.1.2 of http://tools.ietf.org/html/rfc4511
The filter must be a valid LDAP search filter as specified by http://www.ietf.org/rfc/rfc2254.txt
For examples of this syntax, please refer to the “ldap_search_base” examples section.
Default: the value of ldap_search_base
Please note that specifying scope or filter is not supported for searches against an Active Directory Server that might yield a large number of results and trigger the Range Retrieval extension in the response.
Note
If the option “ldap_use_tokengroups” is enabled, the searches against Active Directory will not be restricted and return all groups memberships, even with no GID mapping. It is recommended to disable this feature, if group names are not being displayed correctly.
ldap_sudo_search_base (string)
syntax:
search_base[?scope?[filter][?search_base?scope?[filter]]*]
The scope can be one of "base", "onelevel" or "subtree". The scope functions as specified in section 4.5.1.2 of http://tools.ietf.org/html/rfc4511
The filter must be a valid LDAP search filter as specified by http://www.ietf.org/rfc/rfc2254.txt
For examples of this syntax, please refer to the “ldap_search_base” examples section.
Default: the value of ldap_search_base
Please note that specifying scope or filter is not supported for searches against an Active Directory Server that might yield a large number of results and trigger the Range Retrieval extension in the response.
ldap_autofs_search_base (string)
syntax:
search_base[?scope?[filter][?search_base?scope?[filter]]*]
The scope can be one of "base", "onelevel" or "subtree". The scope functions as specified in section 4.5.1.2 of http://tools.ietf.org/html/rfc4511
The filter must be a valid LDAP search filter as specified by http://www.ietf.org/rfc/rfc2254.txt
For examples of this syntax, please refer to the “ldap_search_base” examples section.
Default: the value of ldap_search_base
Please note that specifying scope or filter is not supported for searches against an Active Directory Server that might yield a large number of results and trigger the Range Retrieval extension in the response.
FAILOVER¶
The failover feature allows back ends to automatically switch to a different server if the current server fails.
Failover Syntax¶
The list of servers is given as a comma-separated list; any number of spaces is allowed around the comma. The servers are listed in order of preference. The list can contain any number of servers.
For each failover-enabled config option, two variants exist: primary and backup. The idea is that servers in the primary list are preferred and backup servers are only searched if no primary servers can be reached. If a backup server is selected, a timeout of 31 seconds is set. After this timeout SSSD will periodically try to reconnect to one of the primary servers. If it succeeds, it will replace the current active (backup) server.
The Failover Mechanism¶
The failover mechanism distinguishes between a machine and a service. The back end first tries to resolve the hostname of a given machine; if this resolution attempt fails, the machine is considered offline. No further attempts are made to connect to this machine for any other service. If the resolution attempt succeeds, the back end tries to connect to a service on this machine. If the service connection attempt fails, then only this particular service is considered offline and the back end automatically switches over to the next service. The machine is still considered online and might still be tried for another service.
Further connection attempts are made to machines or services marked as offline after a specified period of time; this is currently hard coded to 30 seconds.
If there are no more machines to try, the back end as a whole switches to offline mode, and then attempts to reconnect every 30 seconds.
Failover time outs and tuning¶
Resolving a server to connect to can be as simple as running a single DNS query or can involve several steps, such as finding the correct site or trying out multiple host names in case some of the configured servers are not reachable. The more complex scenarios can take some time and SSSD needs to balance between providing enough time to finish the resolution process but on the other hand, not trying for too long before falling back to offline mode. If the SSSD debug logs show that the server resolution is timing out before a live server is contacted, you can consider changing the time outs.
This section lists the available tunables. Please refer to their description in the sssd.conf(5), manual page.
dns_resolver_server_timeout
Default: 1000
dns_resolver_op_timeout
Default: 3
dns_resolver_timeout
Default: 6
For LDAP-based providers, the resolve operation is performed as part of an LDAP connection operation. Therefore, also the “ldap_opt_timeout” timeout should be set to a larger value than “dns_resolver_timeout” which in turn should be set to a larger value than “dns_resolver_op_timeout” which should be larger than “dns_resolver_server_timeout”.
SERVICE DISCOVERY¶
The service discovery feature allows back ends to automatically find the appropriate servers to connect to using a special DNS query. This feature is not supported for backup servers.
Configuration¶
If no servers are specified, the back end automatically uses service discovery to try to find a server. Optionally, the user may choose to use both fixed server addresses and service discovery by inserting a special keyword, “_srv_”, in the list of servers. The order of preference is maintained. This feature is useful if, for example, the user prefers to use service discovery whenever possible, and fall back to a specific server when no servers can be discovered using DNS.
The domain name¶
Please refer to the “dns_discovery_domain” parameter in the sssd.conf(5) manual page for more details.
The protocol¶
The queries usually specify _tcp as the protocol. Exceptions are documented in respective option description.
See Also¶
For more information on the service discovery mechanism, refer to RFC 2782.
ID MAPPING¶
The ID-mapping feature allows SSSD to act as a client of Active Directory without requiring administrators to extend user attributes to support POSIX attributes for user and group identifiers.
NOTE: When ID-mapping is enabled, the uidNumber and gidNumber attributes are ignored. This is to avoid the possibility of conflicts between automatically-assigned and manually-assigned values. If you need to use manually-assigned values, ALL values must be manually-assigned.
Please note that changing the ID mapping related configuration options will cause user and group IDs to change. At the moment, SSSD does not support changing IDs, so the SSSD database must be removed. Because cached passwords are also stored in the database, removing the database should only be performed while the authentication servers are reachable, otherwise users might get locked out. In order to cache the password, an authentication must be performed. It is not sufficient to use sss_cache(8) to remove the database, rather the process consists of:
Moreover, as the change of IDs might necessitate the adjustment of other system properties such as file and directory ownership, it's advisable to plan ahead and test the ID mapping configuration thoroughly.
Mapping Algorithm¶
Active Directory provides an objectSID for every user and group object in the directory. This objectSID can be broken up into components that represent the Active Directory domain identity and the relative identifier (RID) of the user or group object.
The SSSD ID-mapping algorithm takes a range of available UIDs and divides it into equally-sized component sections - called "slices"-. Each slice represents the space available to an Active Directory domain.
When a user or group entry for a particular domain is encountered for the first time, the SSSD allocates one of the available slices for that domain. In order to make this slice-assignment repeatable on different client machines, we select the slice based on the following algorithm:
The SID string is passed through the murmurhash3 algorithm to convert it to a 32-bit hashed value. We then take the modulus of this value with the total number of available slices to pick the slice.
NOTE: It is possible to encounter collisions in the hash and subsequent modulus. In these situations, we will select the next available slice, but it may not be possible to reproduce the same exact set of slices on other machines (since the order that they are encountered will determine their slice). In this situation, it is recommended to either switch to using explicit POSIX attributes in Active Directory (disabling ID-mapping) or configure a default domain to guarantee that at least one is always consistent. See “Configuration” for details.
Configuration¶
Minimum configuration (in the “[domain/DOMAINNAME]” section):
ldap_id_mapping = True ldap_schema = ad
The default configuration results in configuring 10,000 slices, each capable of holding up to 200,000 IDs, starting from 200,000 and going up to 2,000,200,000. This should be sufficient for most deployments.
Advanced Configuration
ldap_idmap_range_min (integer)
NOTE: This option is different from “min_id” in that “min_id” acts to filter the output of requests to this domain, whereas this option controls the range of ID assignment. This is a subtle distinction, but the good general advice would be to have “min_id” be less-than or equal to “ldap_idmap_range_min”
Default: 200000
ldap_idmap_range_max (integer)
NOTE: This option is different from “max_id” in that “max_id” acts to filter the output of requests to this domain, whereas this option controls the range of ID assignment. This is a subtle distinction, but the good general advice would be to have “max_id” be greater-than or equal to “ldap_idmap_range_max”
Default: 2000200000
ldap_idmap_range_size (integer)
NOTE: The value of this option must be at least as large as the highest user RID planned for use on the Active Directory server. User lookups and login will fail for any user whose RID is greater than this value.
For example, if your most recently-added Active Directory user has objectSid=S-1-5-21-2153326666-2176343378-3404031434-1107, “ldap_idmap_range_size” must be at least 1108 as range size is equal to maximal SID minus minimal SID plus one (e.g. 1108 = 1107 - 0 + 1).
It is important to plan ahead for future expansion, as changing this value will result in changing all of the ID mappings on the system, leading to users with different local IDs than they previously had.
Default: 200000
ldap_idmap_default_domain_sid (string)
Default: not set
ldap_idmap_default_domain (string)
Default: not set
ldap_idmap_autorid_compat (boolean)
When this option is configured, domains will be allocated starting with slice zero and increasing monotonically with each additional domain.
NOTE: This algorithm is non-deterministic (it depends on the order that users and groups are requested). If this mode is required for compatibility with machines running winbind, it is recommended to also use the “ldap_idmap_default_domain_sid” option to guarantee that at least one domain is consistently allocated to slice zero.
Default: False
ldap_idmap_helper_table_size (integer)
Note: Additional secondary slices might be generated when SID is being mapped to UNIX id and RID part of SID is out of range for secondary slices generated so far. If value of ldap_idmap_helper_table_size is equal to 0 then no additional secondary slices are generated.
Default: 10
Well-Known SIDs¶
SSSD supports to look up the names of Well-Known SIDs, i.e. SIDs with a special hardcoded meaning. Since the generic users and groups related to those Well-Known SIDs have no equivalent in a Linux/UNIX environment no POSIX IDs are available for those objects.
The SID name space is organized in authorities which can be seen as different domains. The authorities for the Well-Known SIDs are
The capitalized version of these names are used as domain names when returning the fully qualified name of a Well-Known SID.
Since some utilities allow to modify SID based access control information with the help of a name instead of using the SID directly SSSD supports to look up the SID by the name as well. To avoid collisions only the fully qualified names can be used to look up Well-Known SIDs. As a result the domain names “NULL AUTHORITY”, “WORLD AUTHORITY”, “LOCAL AUTHORITY”, “CREATOR AUTHORITY”, “MANDATORY LABEL AUTHORITY”, “AUTHENTICATION AUTHORITY”, “NT AUTHORITY” and “BUILTIN” should not be used as domain names in sssd.conf.
EXAMPLE¶
The following example assumes that SSSD is correctly configured and LDAP is set to one of the domains in the [domains] section.
[domain/LDAP] id_provider = ldap auth_provider = ldap ldap_uri = ldap://ldap.mydomain.org ldap_search_base = dc=mydomain,dc=org ldap_tls_reqcert = demand cache_credentials = true
LDAP ACCESS FILTER EXAMPLE¶
The following example assumes that SSSD is correctly configured and to use the ldap_access_order=lockout.
[domain/LDAP] id_provider = ldap auth_provider = ldap access_provider = ldap ldap_access_order = lockout ldap_pwdlockout_dn = cn=ppolicy,ou=policies,dc=mydomain,dc=org ldap_uri = ldap://ldap.mydomain.org ldap_search_base = dc=mydomain,dc=org ldap_tls_reqcert = demand cache_credentials = true
NOTES¶
The descriptions of some of the configuration options in this manual page are based on the ldap.conf(5) manual page from the OpenLDAP 2.4 distribution.
SEE ALSO¶
sssd(8), sssd.conf(5), sssd-ldap(5), sssd-ldap-attributes(5), sssd-krb5(5), sssd-simple(5), sssd-ipa(5), sssd-ad(5), sssd-sudo(5), sssd-session-recording(5), sss_cache(8), sss_debuglevel(8), sss_obfuscate(8), sss_seed(8), sssd_krb5_locator_plugin(8), sss_ssh_authorizedkeys(8), sss_ssh_knownhostsproxy(8), sssd-ifp(5), pam_sss(8). sss_rpcidmapd(5)
AUTHORS¶
The SSSD upstream - https://github.com/SSSD/sssd/
| 10/01/2024 | SSSD |