이 콘텐츠는 선택한 언어로 제공되지 않습니다.
Chapter 20. Directory Servers
20.1. OpenLDAP
LDAP (Lightweight Directory Access Protocol) is a set of open protocols used to access centrally stored information over a network. It is based on the X.500 standard for directory sharing, but is less complex and resource-intensive. For this reason, LDAP is sometimes referred to as “X.500 Lite”.
	20.1.1. Introduction to LDAP
Important
Important
SSLv3 protocol for security. OpenLDAP is one of the system components that do not provide configuration parameters that allow SSLv3 to be effectively disabled. To mitigate the risk, it is recommended that you use the stunnel command to provide a secure tunnel, and disable stunnel from using SSLv3. For more information on using stunnel, see the Red Hat Enterprise Linux 6 Security Guide.
			20.1.1.1. LDAP Terminology
- entry
- A single unit within an LDAP directory. Each entry is identified by its unique Distinguished Name (DN).
- attribute
- Information directly associated with an entry. For example, if an organization is represented as an LDAP entry, attributes associated with this organization might include an address, a fax number, etc. Similarly, people can be represented as entries with common attributes such as personal telephone number or email address.An attribute can either have a single value, or an unordered space-separated list of values. While certain attributes are optional, others are required. Required attributes are specified using theobjectClassdefinition, and can be found in schema files located in the/etc/openldap/slapd.d/cn=config/cn=schema/directory.The assertion of an attribute and its corresponding value is also referred to as a Relative Distinguished Name (RDN). Unlike distinguished names that are unique globally, a relative distinguished name is only unique per entry.
- LDIF
- The LDAP Data Interchange Format (LDIF) is a plain text representation of an LDAP entry. It takes the following form:[id] dn: distinguished_name attribute_type: attribute_value attribute_type: attribute_value ... [id] dn: distinguished_name attribute_type: attribute_value attribute_type: attribute_value ...Copy to Clipboard Copied! Toggle word wrap Toggle overflow The optional id is a number determined by the application that is used to edit the entry. Each entry can contain as many attribute_type and attribute_value pairs as needed, as long as they are all defined in a corresponding schema file. A blank line indicates the end of an entry.
20.1.1.2. OpenLDAP Features
- LDAPv3 Support — Many of the changes in the protocol since LDAP version 2 are designed to make LDAP more secure. Among other improvements, this includes the support for Simple Authentication and Security Layer (SASL), and Transport Layer Security (TLS) protocols.
- LDAP Over IPC — The use of inter-process communication (IPC) enhances security by eliminating the need to communicate over a network.
- IPv6 Support — OpenLDAP is compliant with Internet Protocol version 6 (IPv6), the next generation of the Internet Protocol.
- LDIFv1 Support — OpenLDAP is fully compliant with LDIF version 1.
- Updated C API — The current C API improves the way programmers can connect to and use LDAP directory servers.
- Enhanced Standalone LDAP Server — This includes an updated access control system, thread pooling, better tools, and much more.
20.1.1.3. OpenLDAP Server Setup
- Install the OpenLDAP suite. See Section 20.1.2, “Installing the OpenLDAP Suite” for more information on required packages.
- Customize the configuration as described in Section 20.1.3, “Configuring an OpenLDAP Server”.
- Start theslapdservice as described in Section 20.1.4, “Running an OpenLDAP Server”.
- Use theldapaddutility to add entries to the LDAP directory.
- Use theldapsearchutility to verify that theslapdservice is accessing the information correctly.
20.1.2. Installing the OpenLDAP Suite
| Package | Description | 
|---|---|
| openldap | A package containing the libraries necessary to run the OpenLDAP server and client applications. | 
| openldap-clients | A package containing the command-line utilities for viewing and modifying directories on an LDAP server. | 
| openldap-servers | A package containing both the services and utilities to configure and run an LDAP server. This includes the Standalone LDAP Daemon, slapd. | 
| compat-openldap | A package containing the OpenLDAP compatibility libraries. | 
| Package | Description | 
|---|---|
| sssd | A package containing the System Security Services Daemon (SSSD), a set of daemons to manage access to remote directories and authentication mechanisms. It provides the Name Service Switch (NSS) and the Pluggable Authentication Modules (PAM) interfaces toward the system and a pluggable back-end system to connect to multiple different account sources. | 
| mod_authz_ldap | 
							A package containing  mod_authz_ldap, the LDAP authorization module for the Apache HTTP Server. This module uses the short form of the distinguished name for a subject and the issuer of the client SSL certificate to determine the distinguished name of the user within an LDAP directory. It is also capable of authorizing users based on attributes of that user's LDAP directory entry, determining access to assets based on the user and group privileges of the asset, and denying access for users with expired passwords. Note that themod_sslmodule is required when using themod_authz_ldapmodule. | 
yum command in the following form:
		yum install package
yum install packageyum install openldap openldap-clients openldap-servers
~]# yum install openldap openldap-clients openldap-serversroot) to run this command. For more information on how to install new packages in Red Hat Enterprise Linux, see Section 8.2.4, “Installing Packages”.
		20.1.2.1. Overview of OpenLDAP Server Utilities
slapd service:
			| Command | Description | 
|---|---|
| slapacl | Allows you to check the access to a list of attributes. | 
| slapadd | Allows you to add entries from an LDIF file to an LDAP directory. | 
| slapauth | Allows you to check a list of IDs for authentication and authorization permissions. | 
| slapcat | Allows you to pull entries from an LDAP directory in the default format and save them in an LDIF file. | 
| slapdn | Allows you to check a list of Distinguished Names (DNs) based on available schema syntax. | 
| slapindex | Allows you to re-index the slapddirectory based on the current content. Run this utility whenever you change indexing options in the configuration file. | 
| slappasswd | Allows you to create an encrypted user password to be used with the ldapmodifyutility, or in theslapdconfiguration file. | 
| slapschema | Allows you to check the compliance of a database with the corresponding schema. | 
| slaptest | Allows you to check the LDAP server configuration. | 
Important
root can run slapadd, the slapd service runs as the ldap user. Because of this, the directory server is unable to modify any files created by slapadd. To correct this issue, after running the slapd utility, type the following at a shell prompt:
				chown -R ldap:ldap /var/lib/ldap
~]# chown -R ldap:ldap /var/lib/ldapWarning
slapd service before using slapadd, slapcat, or slapindex. You can do so by typing the following at a shell prompt:
				service slapd stop
~]# service slapd stop
Stopping slapd:                                            [  OK  ]slapd service, see Section 20.1.4, “Running an OpenLDAP Server”.
				20.1.2.2. Overview of OpenLDAP Client Utilities
| Command | Description | 
|---|---|
| ldapadd | Allows you to add entries to an LDAP directory, either from a file, or from standard input. It is a symbolic link to ldapmodify -a. | 
| ldapcompare | Allows you to compare given attribute with an LDAP directory entry. | 
| ldapdelete | Allows you to delete entries from an LDAP directory. | 
| ldapexop | Allows you to perform extended LDAP operations. | 
| ldapmodify | Allows you to modify entries in an LDAP directory, either from a file, or from standard input. | 
| ldapmodrdn | Allows you to modify the RDN value of an LDAP directory entry. | 
| ldappasswd | Allows you to set or change the password for an LDAP user. | 
| ldapsearch | Allows you to search LDAP directory entries. | 
| ldapurl | Allows you to compose or decompose LDAP URLs. | 
| ldapwhoami | Allows you to perform a whoamioperation on an LDAP server. | 
ldapsearch, each of these utilities is more easily used by referencing a file containing the changes to be made rather than typing a command for each entry to be changed within an LDAP directory. The format of such a file is outlined in the man page for each utility.
			20.1.2.3. Overview of Common LDAP Client Applications
20.1.3. Configuring an OpenLDAP Server
/etc/openldap/ directory. Table 20.5, “List of OpenLDAP configuration files and directories” highlights the most important files and directories within this directory.
		slapd service uses a configuration database located in the /etc/openldap/slapd.d/ directory and only reads the old /etc/openldap/slapd.conf configuration file if this directory does not exist. If you have an existing slapd.conf file from a previous installation, you can either wait for the openldap-servers package to convert it to the new format the next time you update this package, or type the following at a shell prompt as root to convert it immediately:
		slaptest -f /etc/openldap/slapd.conf -F /etc/openldap/slapd.d/
~]# slaptest -f /etc/openldap/slapd.conf -F /etc/openldap/slapd.d/slapd configuration consists of LDIF entries organized in a hierarchical directory structure, and the recommended way to edit these entries is to use the server utilities described in Section 20.1.2.1, “Overview of OpenLDAP Server Utilities”.
		Important
slapd service unable to start. Because of this, it is strongly advised that you avoid editing the LDIF files within the /etc/openldap/slapd.d/ directory directly.
			20.1.3.1. Changing the Global Configuration
/etc/openldap/slapd.d/cn=config.ldif file. The following directives are commonly used:
			-   olcAllows
- TheolcAllowsdirective allows you to specify which features to enable. It takes the following form:olcAllows: feature olcAllows: featureCopy to Clipboard Copied! Toggle word wrap Toggle overflow It accepts a space-separated list of features as described in Table 20.6, “Available olcAllows options”. The default option isbind_v2.Expand Table 20.6. Available olcAllows options Option Description bind_v2Enables the acceptance of LDAP version 2 bind requests. bind_anon_credEnables an anonymous bind when the Distinguished Name (DN) is empty. bind_anon_dnEnables an anonymous bind when the Distinguished Name (DN) is not empty. update_anonEnables processing of anonymous update operations. proxy_authz_anonEnables processing of anonymous proxy authorization control. Example 20.1. Using the olcAllows directive olcAllows: bind_v2 update_anon olcAllows: bind_v2 update_anonCopy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcConnMaxPending
- TheolcConnMaxPendingdirective allows you to specify the maximum number of pending requests for an anonymous session. It takes the following form:olcConnMaxPending: number olcConnMaxPending: numberCopy to Clipboard Copied! Toggle word wrap Toggle overflow The default option is100.Example 20.2. Using the olcConnMaxPending directive olcConnMaxPending: 100 olcConnMaxPending: 100Copy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcConnMaxPendingAuth
- TheolcConnMaxPendingAuthdirective allows you to specify the maximum number of pending requests for an authenticated session. It takes the following form:olcConnMaxPendingAuth: number olcConnMaxPendingAuth: numberCopy to Clipboard Copied! Toggle word wrap Toggle overflow The default option is1000.Example 20.3. Using the olcConnMaxPendingAuth directive olcConnMaxPendingAuth: 1000 olcConnMaxPendingAuth: 1000Copy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcDisallows
- TheolcDisallowsdirective allows you to specify which features to disable. It takes the following form:olcDisallows: feature olcDisallows: featureCopy to Clipboard Copied! Toggle word wrap Toggle overflow It accepts a space-separated list of features as described in Table 20.7, “Available olcDisallows options”. No features are disabled by default.Expand Table 20.7. Available olcDisallows options Option Description bind_anonDisables the acceptance of anonymous bind requests. bind_simpleDisables the simple bind authentication mechanism. tls_2_anonDisables the enforcing of an anonymous session when the STARTTLS command is received. tls_authcDisallows the STARTTLS command when authenticated. Example 20.4. Using the olcDisallows directive olcDisallows: bind_anon olcDisallows: bind_anonCopy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcIdleTimeout
- TheolcIdleTimeoutdirective allows you to specify how many seconds to wait before closing an idle connection. It takes the following form:olcIdleTimeout: number olcIdleTimeout: numberCopy to Clipboard Copied! Toggle word wrap Toggle overflow This option is disabled by default (that is, set to0).Example 20.5. Using the olcIdleTimeout directive olcIdleTimeout: 180 olcIdleTimeout: 180Copy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcLogFile
- TheolcLogFiledirective allows you to specify a file in which to write log messages. It takes the following form:olcLogFile: file_name olcLogFile: file_nameCopy to Clipboard Copied! Toggle word wrap Toggle overflow The log messages are written to standard error by default.Example 20.6. Using the olcLogFile directive olcLogFile: /var/log/slapd.log olcLogFile: /var/log/slapd.logCopy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcReferral
- TheolcReferraloption allows you to specify a URL of a server to process the request in case the server is not able to handle it. It takes the following form:olcReferral: URL olcReferral: URLCopy to Clipboard Copied! Toggle word wrap Toggle overflow This option is disabled by default.Example 20.7. Using the olcReferral directive olcReferral: ldap://root.openldap.org olcReferral: ldap://root.openldap.orgCopy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcWriteTimeout
- TheolcWriteTimeoutoption allows you to specify how many seconds to wait before closing a connection with an outstanding write request. It takes the following form:olcWriteTimeout olcWriteTimeoutCopy to Clipboard Copied! Toggle word wrap Toggle overflow This option is disabled by default (that is, set to0).Example 20.8. Using the olcWriteTimeout directive olcWriteTimeout: 180 olcWriteTimeout: 180Copy to Clipboard Copied! Toggle word wrap Toggle overflow 
20.1.3.2. Changing the Database-Specific Configuration
/etc/openldap/slapd.d/cn=config/olcDatabase={2}bdb.ldif file. The following directives are commonly used in a database-specific configuration:
			-   olcReadOnly
- TheolcReadOnlydirective allows you to use the database in a read-only mode. It takes the following form:olcReadOnly: boolean olcReadOnly: booleanCopy to Clipboard Copied! Toggle word wrap Toggle overflow It accepts eitherTRUE(enable the read-only mode), orFALSE(enable modifications of the database). The default option isFALSE.Example 20.9. Using the olcReadOnly directive olcReadOnly: TRUE olcReadOnly: TRUECopy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcRootDN
- TheolcRootDNdirective allows you to specify the user that is unrestricted by access controls or administrative limit parameters set for operations on the LDAP directory. It takes the following form:olcRootDN: distinguished_name olcRootDN: distinguished_nameCopy to Clipboard Copied! Toggle word wrap Toggle overflow It accepts a Distinguished Name (DN). The default option iscn=Manager,dc=my-domain,dc=com.Example 20.10. Using the olcRootDN directive olcRootDN: cn=root,dc=example,dc=com olcRootDN: cn=root,dc=example,dc=comCopy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcRootPW
- TheolcRootPWdirective allows you to set a password for the user that is specified using theolcRootDNdirective. It takes the following form:olcRootPW: password olcRootPW: passwordCopy to Clipboard Copied! Toggle word wrap Toggle overflow It accepts either a plain text string, or a hash. To generate a hash, type the following at a shell prompt:slappaswd ~]$ slappaswd New password: Re-enter new password: {SSHA}WczWsyPEnMchFf1GRTweq2q7XJcvmSxDCopy to Clipboard Copied! Toggle word wrap Toggle overflow Example 20.11. Using the olcRootPW directive olcRootPW: {SSHA}WczWsyPEnMchFf1GRTweq2q7XJcvmSxDolcRootPW: {SSHA}WczWsyPEnMchFf1GRTweq2q7XJcvmSxDCopy to Clipboard Copied! Toggle word wrap Toggle overflow 
-   olcSuffix
- TheolcSuffixdirective allows you to specify the domain for which to provide information. It takes the following form:olcSuffix: domain_name olcSuffix: domain_nameCopy to Clipboard Copied! Toggle word wrap Toggle overflow It accepts a fully qualified domain name (FQDN). The default option isdc=my-domain,dc=com.Example 20.12. Using the olcSuffix directive olcSuffix: dc=example,dc=com olcSuffix: dc=example,dc=comCopy to Clipboard Copied! Toggle word wrap Toggle overflow 
20.1.3.3. Extending Schema
/etc/openldap/slapd.d/cn=config/cn=schema/ directory also contains LDAP definitions that were previously located in /etc/openldap/schema/. It is possible to extend the schema used by OpenLDAP to support additional attribute types and object classes using the default schema files as a guide. However, this task is beyond the scope of this chapter. For more information on this topic, see http://www.openldap.org/doc/admin/schema.html.
			20.1.4. Running an OpenLDAP Server
20.1.4.1. Starting the Service
slapd service, type the following at a shell prompt:
			service slapd start
~]# service slapd start
Starting slapd:                                            [  OK  ]chkconfig slapd on
~]# chkconfig slapd on20.1.4.2. Stopping the Service
slapd service, type the following at a shell prompt:
			service slapd stop
~]# service slapd stop
Stopping slapd:                                            [  OK  ]chkconfig slapd off
~]# chkconfig slapd off20.1.4.3. Restarting the Service
slapd service, type the following at a shell prompt:
			service slapd restart
~]# service slapd restart
Stopping slapd:                                            [  OK  ]
Starting slapd:                                            [  OK  ]20.1.4.4. Checking the Service Status
service slapd status
~]# service slapd status
slapd (pid  3672) is running...20.1.5. Configuring a System to Authenticate Using OpenLDAP
yum install openldap openldap-clients sssd
~]# yum install openldap openldap-clients sssd20.1.5.1. Migrating Old Authentication Information to LDAP Format
yum install migrationtools
~]# yum install migrationtools/usr/share/migrationtools/ directory. Once installed, edit the /usr/share/migrationtools/migrate_common.ph file and change the following lines to reflect the correct domain, for example:
			Default DNS domain Default base
# Default DNS domain
$DEFAULT_MAIL_DOMAIN = "example.com";
# Default base
$DEFAULT_BASE = "dc=example,dc=com";migrate_all_online.sh script with the default base set to dc=example,dc=com, type:
			export DEFAULT_BASE="dc=example,dc=com" \ /usr/share/migrationtools/migrate_all_online.sh
~]# export DEFAULT_BASE="dc=example,dc=com" \
/usr/share/migrationtools/migrate_all_online.sh| Existing Name Service | Is LDAP Running? | Script to Use | 
|---|---|---|
| /etcflat files | yes | migrate_all_online.sh | 
| /etcflat files | no | migrate_all_offline.sh | 
| NetInfo | yes | migrate_all_netinfo_online.sh | 
| NetInfo | no | migrate_all_netinfo_offline.sh | 
| NIS (YP) | yes | migrate_all_nis_online.sh | 
| NIS (YP) | no | migrate_all_nis_offline.sh | 
README and the migration-tools.txt files in the /usr/share/doc/migrationtools-version/ directory.
			20.1.6. Additional Resources
20.1.6.1. Installed Documentation
- /usr/share/doc/openldap-servers-version/guide.html
- A copy of the OpenLDAP Software Administrator's Guide.
- /usr/share/doc/openldap-servers-version/README.schema
- A README file containing the description of installed schema files.
- Client Applications
- man ldapadd— Describes how to add entries to an LDAP directory.
- man ldapdelete— Describes how to delete entries within an LDAP directory.
- man ldapmodify— Describes how to modify entries within an LDAP directory.
- man ldapsearch— Describes how to search for entries within an LDAP directory.
- man ldappasswd— Describes how to set or change the password of an LDAP user.
- man ldapcompare— Describes how to use the- ldapcomparetool.
- man ldapwhoami— Describes how to use the- ldapwhoamitool.
- man ldapmodrdn— Describes how to modify the RDNs of entries.
 
- Server Applications
- man slapd— Describes command-line options for the LDAP server.
 
- Administrative Applications
- man slapadd— Describes command-line options used to add entries to a- slapddatabase.
- man slapcat— Describes command-line options used to generate an LDIF file from a- slapddatabase.
- man slapindex— Describes command-line options used to regenerate an index based upon the contents of a- slapddatabase.
- man slappasswd— Describes command-line options used to generate user passwords for LDAP directories.
 
- Configuration Files
- man ldap.conf— Describes the format and options available within the configuration file for LDAP clients.
- man slapd-config— Describes the format and options available within the configuration directory.
 
20.1.6.2. Useful Websites
- http://www.openldap.org/doc/admin24/
- The current version of the OpenLDAP Software Administrator's Guide.