/var/nis/NIS+LDAPmapping (System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP))

System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP)

`/var/nis/NIS+LDAPmapping`

The name of the above configuration can be changed via the -m option of rpc.nisd(1M). The presence of the NIS+LDAPmapping file serves as a master switch for NIS+/LDAP mapping.

If you use a name other than the default for the mapping file, you will have to edit the /etc/init.d/rpc boot script to specify the mapping file name on the rpc.nisd startup line.

For each NIS+ object that should be mapped to and/or from LDAP, the NIS+LDAPmapping file specifies two to five attributes, depending on the object and whether or not the default values are sufficient.

`nisplusLDAPdatabaseIdMapping`

You must establish an alias to be used in the other mapping attributes. If the NIS+ object name is not fully qualified (does not end in a dot), the value of the nisplusLDAPbaseDomain is appended.

For example,

nisplusLDAPdatabaseIdMapping	rpc:rpc.org_dir

defines the database id rpc as an alias for the NIS+ rpc.org_dir table.

Note that NIS+ table objects might appear twice with two different database ids, once for the table object itself (if the object should be mapped to LDAP), and once for the table entries. For example,

nisplusLDAPdatabaseIdMapping	rpc_table:rpc.org_dir
nisplusLDAPdatabaseIdMapping	rpc:rpc.org_dir

defines the database ids rpc_table and rpc as aliases for the rpc.org_dir table. Later definitions will make it clear that rpc_table is used for the rpc.org_dir table object, and rpc for the entries in that table.

`nisplusLDAPentryTtl`

Since the rpc.nisd daemon's local database (in memory and on disk) functions as a cache for LDAP data, the nisplusLDAPentryTtl attribute allows you to set the time-to-live (TTL) values of entries in that cache. There are three TTLs for each database ID. The first two control the initial TTL when the rpc.nisd first loads the corresponding NIS+ object data from disk, and the third TTL is assigned to an object when it is read or refreshed from LDAP.

For example the following results in the rpc.org_dir table object getting an initial TTL randomly selected in the range 21600 to 43200 seconds.

nisplusLDAPentryTtl	rpc_table:21600:43200:43200

When that initial TTL expires and the table object is refreshed from LDAP, the TTL will be set to 43200 seconds.

Similarly the following will assign an initial TTL between 1800 and 3600 seconds to the entries in the rpc.org_dir table when it is first loaded.

nisplusLDAPentryTtl	rpc:1800:3600:3600

Each entry gets its own randomly selected TTL in the range specified. When a table entry expires and is refreshed, the TTL is set to 3600 seconds.

When selecting TTL values, consider the trade-off between performance and consistency. If the TTLs used for LDAP data cached by the rpc.nisd are very long, performance is the same as if rpc.nisd was not mapping data from LDAP at all. However, if the LDAP data is changed (by some entity other than rpc.nisd), it can also take a very long time before that change is visible in NIS+.

Conversely, selecting a very short (or even zero) TTL means that changes to LDAP data are quickly visible in NIS+, but can also impose a significant performance penalty. Typically, an NIS+ operation that also reads data from or writes data to LDAP will take at least two to three times longer (plus the LDAP lookup overhead) than the same operation without LDAP communication. Although performance can vary greatly depending on the hardware resources, scanning a large (tens of thousands or hundreds of thousands of entries) LDAP container to identify NIS+ entries that should be refreshed can take a long time. The rpc.nisd daemon performs this scan in the background, continuing to serve possibly stale data while it is running, but the background scan still consumes CPU and memory on the NIS+ server.

Carefully consider how critical it is to have NIS+ data in close synchronization with LDAP, and select the longest TTL that is acceptable for each NIS+ object. The default (when no nisplusLDAPentryTtl is specified) is 1 hour. The template mapping file /var/nis/NIS+LDAPmapping.template changes this to 12 hours for objects other than table entries. However, there is no auto-recognition of non-entry objects, so if you add mapping for a non-entry object, the TTL will default to 1 hour.

Note –

There are no TTLs for nonexistent objects. Hence, no matter which TTLs are in effect for LDAP-mapped entries in an NIS+ table, a request for an entry that does not exist in NIS+ will query LDAP for that entry.

`nisplusLDAPobjectDN`

For each mapped NIS+ object, nisplusLDAPobjectDN establishes the location in the LDAP DIT where the object data resides. It also allows specification of the action to take when an LDAP entry is deleted. Each nisplusLDAPobjectDN value has three parts. The first specifies where LDAP data is read from, the second to where it is written, and the third what should happen when LDAP data is deleted. Refer to the following example.

nisplusLDAPobjectDN	rpc_table:\ 
										cn=rpc,ou=nisPlus,?base?\
													objectClass=nisplusObjectContainer:\ 
										cn=rpc,ou=nisPlus,?base?\ 
													objectClass=nisplusObjectContainer,\ 
														objectClass=top

The above example shows that the rpc.org_dir table object should be read from the DN cn=rpc,ou=nisPlus, (since the value ends in a comma, the value of the defaultSearchBase attribute is appended), with scope base, and that entries with a value of nisplusObjectContainer for the ObjectClass attribute are selected.

The table object is written to the same place. The delete specification is missing, which implies the default action, which is as follows. If the NIS+ table object is deleted, the entire LDAP entry should also be deleted.

If data should be read from, but not written to LDAP, omit the write portion (and the colon separating it from the read part).

nisplusLDAPobjectDN	rpc_table:\
										cn=rpc,ou=nisPlus,?base?\
										objectClass=nisplusObjectContainer

Note that the nisplusObjectContainer object class is not part of RFC 2307. In order to use it, you must configure your LDAP server as detailed in Mapping NIS+ Objects Other Than Table Entries.

For the rpc.org_dir table entries, you could use the following example.

nisplusLDAPobjectDN rpc:ou=Rpc,?one?objectClass=oncRpc:\
											ou=Rpc,?one?objectClass=onRpc,objectClass=top

The above shows that the table entries are read from and written to the base ou=Rpc. Again, the trailing comma appends the defaultSearchBase value. Select entries that have an objectClass attribute value of oncRpc. When creating an entry in the ou=Rpc container in LDAP, you also must specify top as an objectClass value.

As an example showing a non-default delete specification, consider the following.

nisplusLDAPobjectDN	user_attr:\
										ou=People,?one?objectClass=SolarisUserAttr,\
											solarisAttrKeyValue=*:\
										ou=People,?one?objectClass=SolarisUserAttr:\
											dbid=user_attr_del

The user_attr.org_dir data resides in the ou=People LDAP container, which it shares with account information from other sources, such as the passwd.org_dir NIS+ table.

Select entries in that container that have the solarisAttrKeyValue attribute, since only those contain user_attr.org_dir data. The dbid=user_attr_del portion of the nisplusLDAPobjectDN shows that when an entry in the user_attr.org_dir NIS+ table entry is deleted, deletion of the corresponding LDAP entry (if any) should follow the rules in the rule set identified by the user_attr_del database ID. See nisplusLDAPcolumnFromAttribute for more information.

`nisplusLDAPattributeFromColumn`

nisplusLDAPattributeFromColumn specifies the rules used to map NIS+ data to LDAP. Mapping rules for the other direction is controlled by nisplusLDAPcolumnFromAttribute.

`nisplusLDAPcolumnFromAttribute`

nisplusLDAPcolumnFromAttribute specifies the rules used to map LDAP data to NIS+.

The full entry mapping syntax can be found on NIS+LDAPmapping(4). However, a few examples should make things clearer.

The NIS+ rpc.org_dir table contains four columns called cname, name, numbe, and comment. Therefore, the entries for the NIS+ RPC program number (100300) with the canonical name nisd and the aliases rpc.nisd and nisplusd could be represented by the following NIS+ entries in rpc.org_dir.

nisd nisd 100300	NIS+ server
nisd rpc.nisd 100300	NIS+ server
nisd nisplusd 100300	NIS+ server

Assuming the defaultSearchBase value is dc=some,dc=domain, the corresponding LDAP entry, as listed by ldapsearch(1), would be the following.

cn=nisd,ou=Ppc,dc=some,dc=domain
cn=nisd
cn=rpc.nsid
cn=nisplusd
oncrocnumber=100300
description=NIS+ server
objectclass=oncRpc
objectclass=top

This makes for a simple one-to-one mapping between NIS+ and LDAP data, and the corresponding mapping attribute value going from NIS+ to LDAP is the following.

nisplusLDAPattributeFromColumn \ 
rpc:		dn=("cn=%s,", name), \ 
				cn=cname, \
				cn=name, \
				oncRpcNumber=number, \
				description=comment

This constructs the DN for the entry to be cn=%s, with the value of the cname column substituted for %s.

cn=nisd,

Since the value ends in a comma, the read base value from the nisplusObjectDN is appended, and you have the following.

cn=nisd,ou=Rpc,dc=some,dc=domain

The oncRpcNumber and description attribute values are just simple assignments of the corresponding NIS+ column values. The rpc.nisd will collect the multiple NIS+ entries into one LDAP entry, with multiple cn values to represent the different name column values.

Similarly, the mapping from LDAP to NIS+ would be as follows.

nisplusLDAPcolumnFromAttribute \ 
 					rpc:		cname=cn, \
			 						(name)=(cn), \
									number=oncRpcNumber, \
									comment=description

The above assigns the oncRpcNumber and description values to the corresponding NIS+ columns. The multi-valued cn (denoted by (cn) is mapped to multiple name column values (denoted by (name)). Since the name column cannot be multi-valued, the rpc.nisd creates one NIS+ entry for each cn value.

Finally, the nisplusLDAPattributeFromColumn value is an example of rule sets used for deletion.

nisplusLDAPattributeFromColumn \
user_attr_del:	dn=("uid=%s,", name), \
						SolarisUserQualifier=, \
						SolarisAttrReserved1=, \
 						SolarisAttrReserved2=, \
						SolarisAttrKeyValue=

Again, the user_attr.org_dir data shares the ou=People container with other account information (from the passwd.org_dir and other tables). If an entry in the user_attr.org_dir table is deleted, you probably do not want to delete the entire ou=People entry. Instead, the delete entry above says that when a user_attr.org_dir entry is deleted, the SolarisUserQualifier, SolarisAttrReserved1, SolarisAttrReserved2, and SolarisAttrKeyValue attributes (if any) are deleted from the ou=People entry specified by the following rule.

dn=("uid=%s,", name)

The rest of the LDAP entry is left unchanged.