OpenLDAP Server

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OpenLDAP is a free implementation of the X.500 directory service standards. LDAP stands for Lightweight Directory Access Protocol. The lightweight part comes from the fact it does not implement ALL of the standard. X.500 is quite unwieldy, and much of it has been superseded (e.g. the OSI networking stack) or considered impractical (e.g. such as canonical per entry Distinguished Names) or undesirable (e.g. publishing directories of private entities like businesses).

Introduction to LDAP

LDAP is a directory service. It's similar to a database but with different aims. LDAP is hierarchical database, optimized for reading and replication. It does not have same ACID properties of a standard database.

An LDAP database consists of branches called Distinguished Names or a DNs. Example distinguished names are uid=johnsmith,ou=people,dc=example,dc=com and olcDatabase=config,cn=config. Each DN may have additional branches or more distinguished names. So for the DN ou=people,dc=example,dc=com, it is possible to create a new branch, called uid=johnsmith and thus a new DN. A DN can also have attributes. What these attributes mean is defined in a schema. Schemas define:

  • The Object Indentifier (OID) of the attribute (every attribute has a unique OID)
  • Matching rules (like case sensitivity)
  • Syntax of the attribute (like its type)
  • Whether the attribute is single-valued or multi-valued
  • One special attribute is the objectClass. Object classes:
    • Can be either STRUCTURAL or AUXILIARY. A DN must have exactly one STRUCTURAL object class, and zero or more AUXILIARY object classes.
    • What object classes it derives from
    • Required attributes for the DN.
    • Optional attributes for the DN.

Installing OpenLDAP

Before installing OpenLDAP, some USE flags need to be set or cleared first.

USE flags for net-nds/openldap LDAP suite of application and development tools

argon2 Enable password hashing algorithm from app-crypt/argon2
autoca Automatic Certificate Authority overlay
berkdb Add support for sys-libs/db (Berkeley DB for MySQL)
cleartext Enable use of cleartext passwords
crypt Add support for encryption -- using mcrypt or gpg where applicable
cxx Build support for C++ (bindings, extra libraries, code generation, ...)
debug Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
experimental Enable experimental backend options
gnutls Prefer net-libs/gnutls as SSL/TLS provider (ineffective with USE=-ssl)
iodbc Add support for iODBC library
ipv6 Add support for IP version 6
kerberos Add kerberos support
kinit Enable support for kerberos init
minimal Build libraries & userspace tools only. Does not install any server code
odbc Enable ODBC and SQL backend options
overlays Enable contributed OpenLDAP overlays
pbkdf2 Enable support for pbkdf2 passwords
perl Add optional support/bindings for the Perl language
samba Add support for SAMBA (Windows File and Printer sharing)
sasl Add support for the Simple Authentication and Security Layer
selinux !!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur
sha2 Enable support for pw-sha2 password hashes
smbkrb5passwd Enable overlay for syncing ldap, unix and lanman passwords
ssl Add support for SSL/TLS connections (Secure Socket Layer / Transport Layer Security)
static-libs Build static versions of dynamic libraries as well
syslog Enable support for syslog
systemd Enable use of systemd-specific libraries and features like socket activation or session tracking
tcpd Add support for TCP wrappers
test Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)

On most profiles the minimal USE flag is set, which disables installation of the server and supporting files. The sasl USE flag is recommended for all users, and required for Kerberos users (in addition to the kerberos flag).

The debug is virtually required for OpenLDAP servers - the server produces no output (diagnostic or otherwise) at all in the syslog and the olcLogLevel option has little effect (except for stats), which makes it difficult to troubleshoot. This is different than most users of the flag, where it should normally be turned off

Set the desired flags in /etc/portage/package.use/openldap, as an example:

FILE /etc/portage/package.use/openldap
net-nds/openldap debug -minimal overlays sasl

Once installed, there are 2 sets of utilities: the ldap ones and the slap ones. The ldap ones run against a running LDAP server, whereas the slap ones operate offline on the server database directly.

Introduction to LDIF files

OpenLDAP uses directory entries itself for configuration, so it necessary to use LDIF for bootstrapping. The initial configuration is created as an LDIF file and loaded on the server with slapadd. Once the server is running, the ldapadd and ldapmodify can be used to make further changes. If the server is unable to start, slapmodify can be used to load LDIF files to fix it.

An LDIF file is a plain text file with a particular format. Distinguished names have 5 operations defined on them: add, delete, modify, rename (modrdn), and move (moddn).

A LDIF file looks like this:

CODE Sample LDIF file
dn: uid=ebunny,ou=people,dc=example,dc=com
changetype: add
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
sn:: QnU6bm55Cg==
cn: ebunny
cn: Easter Bunny
# This is a comment
uid: ebunny
uidNumber: 20000
gidNumber: 20000
homeDirectory: /home/ebunny
loginShell: /bin/bash
gecos: This is a store ab
 out a man named Bunny
jpegPhoto:< file:///root/ebunny.jpg

dn: uid=ebunny,ou=people,dc=example,dc=com
changetype: modify
replace: sn
sn: bunny
-
delete: jpegPhoto

dn: uid=sclaus,ou=people,dc=example,dc=com
changetype: delete

Note the following things:

  • Multiple operations can be done in an LDIF file.
  • All LDIF entries start with "dn: " followed by the DN of the entry to operate on.
  • The next line the modification operation requested on the DN.
  • For the modify operation, either add, replace, or delete must be specified.
  • Multiple attributes may be updated in a single modify operation.
  • Multi-valued attributes may be specified multiple times.
  • Binary attributes can be added by suffixing a another colon to end of attribute:.
  • Files may be used as attribute values by suffixing a < to end of attribute:.
  • LDIF lines may continued onto the next line by stating them with a single space.
  • Comments are started by a # in column 1.

Add operation

To add a DN, start the entry with "dn: " followed by the DN to add. The next line must be "changetype: add". On each additional line, specify the attributes to add along with their values in the format attribute: value. The add operation will fail if the DN already exists.

CODE Add a DN
dn: uid=ebunny,ou=people,dc=example,dc=com
changetype: add
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
sn: bunny
cn: ebunny
cn: Easter Bunny
uid: ebunny
uidNumber: 20000
gidNumber: 20000
homeDirectory: /home/ebunny
loginShell: /bin/bash
gecos: Easter Bunny

Process the file with ldapmodify/slapmodify:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f filename.ldif

If the file contains only add operations, the ldapadd/slapddd utilities may be used instead. In that case, the changetype: add lines are optional.

root #ldapadd -H ldapi:/// -Y EXTERNAL -f filename.ldif

Delete operation

To delete a DN, start the entry with "dn: " followed by the DN to delete. The next line must be "changetype: delete". The delete operation will fail if the DN does not exist.

CODE Delete a DN
dn: uid=ebunny,ou=people,dc=example,dc=com
changetype: delete

Only "leaf" DNs can be deleted. Process the file with ldapmodify/slapmodify.

root #ldapmodify -H ldapi:// -Y EXTERNAL -f filename.ldif

The DN can alsp be deleted directly using the ldapdelete command

root #ldapdelete -H ldapi:// -Y EXTERNAL uid=ebunny,ou=people,dc=example,dc=com

Modify operation

To modify a DN, start the entry with "dn: " followed by the DN to modify. The next line must be "changetype: modify". There are 3 sub-operations for modify, each with its own syntax.

Process the file with ldapmodify/slapmodify:

root #ldapmodify -H ldapi:// -Y EXTERNAL -f filename.ldif

Add Attribute

To add an attribute to a DN, the next line should be "add: " follow by the attribute name to add. The next line is in the format attribute: value. Multi-valued attributes may be specific multiple times, one of each value. If the attribute doesn't exist, it's created. If it already exists and it's multi-valued, an additional value is added. If it already exists and it's not multi-valued, the operation fails.

CODE Add an attribute
dn: olcDatabase={2}mdb,cn=config
changetype: add
add: olcLimits
olcLimits: dn.exact="cn=replicator,dc=example,dc=com"               
  time.soft=unlimited time.hard=unlimited
  size.soft=unlimited size.hard=unlimited

Delete Attribute

To delete an attribute from a DN, the next line should be "delete: " follow by the attribute name to delete. If the attribute is multi-valued, ALL values are deleted. The operation fails if the attribute does not exist.

CODE Delete an attribute
dn: olcDatabase={2}mdb,cn=config
changetype: modify
delete: olcRootPW

Replace Attribute

To replace an attribute for a DN, the next line should be "replace: " follow by the attribute name to replace. The next line is in the format attribute: value. The attribute: value may be specified multiple times but the attribute must be the same. If the attribute is multi-valued, ALL values are replaced. If the attribute does not exist, it is created. If multiple values are added to a non-multi-valued attribute, the operation fails.

CODE Replace an attribute
dn: olcDatabase={2}mdb,cn=config
changetype: modify
replace: olcAccess
olcAccess: to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external
 ,cn=auth" manage
  by dn.exact="cn=replicator,dc=example,dc=com" read
  by * break
olcAccess: to attrs=userPassword
  by self write
  by anonymous auth
  by * none
olcAccess: to *
  by * read
Note
The replace operation is NOT atomic. If an attribute needs to be atomically replaced, do a delete then an add in the same modify statement instead using the section below

Modify multiple attributes on a single DN

A modifiy operation may change several attributes in a single statement. Separate each attribute change on the DN with a dash (-) on its own line:

CODE Add an attribute
dn: olcDatabase={2}mdb,cn=config
changetype: modify
replace: olcAccess
olcAccess: to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external
 ,cn=auth" manage
  by dn.exact="cn=replicator,dc=example,dc=com" read
olcAccess: to attrs=userPassword
  by self write
  by anonymous auth
  by * none
olcAccess: to *
  by * read
-
changetype: add
add: olcLimits
olcLimits: dn.exact="cn=replicator,dc=example,dc=com"               
  time.soft=unlimited time.hard=unlimited
  size.soft=unlimited size.hard=unlimited
-
delete: olcRootPW

Note this a little different that 3 different modify operations: They must all succeed, or none do.

Rename (modrdn)

To rename a DN, start the entry with "dn: " followed by the DN to rename. The next line must be "changetype: modrdn" (stands for Modify Relative DN). On the line after, specify "newrdn: " and the new name. On the next line, specify "deleteoldrdn: " and either 0 or 1, 0 keeps the old entry as an alias; 1 does not.

CODE Rename a DN
dn: ou=people,dc=example,dc=com
changetype: modrdn
newrdn: ou=aliens
deleteoldrdn: 1

Process the file with ldapmodify (None of the backends current implement the modrdn operation for slapmodify)

root #ldapmodify -H ldapi:// -Y EXTERNAL -f filename.ldif

The DN can also be renamed directly using the ldapmodrn utlity:

root #ldapmodrdn -H ldapi:/// -Y EXTERNAL ou=people,dc=example,dc=com ou=aliens

Move (moddn)

To move a DN, start the entry with "dn: " followed by the DN to rename. The next line must be "changetype: moddn" (stands for Modify DN). On the line after, specify "newsuperior: " and the new DN to place this DN under, pruning one part of the tree and grafting onto another . On the next line, specify "deleteoldrdn: " and either 0 or 1, 0 keeps the old entry as an alias; 1 does not.

CODE Move a a DN
dn: uid=ebunny,ou=people,dc=example,dc=com
changetype: moddn
newsuperior: ou=animals,dc=example,dc=com
deleteoldrdn: 1

Process the file with ldapmodify/slapmodify:

root #ldapmodify -H ldapi:// -Y EXTERNAL -f filename.ldif

LDAP hierarchy and searches

LDAP directories are hierarchical. The OU (organizational unit) typically used to divide up the directory, and an OU can have other OUs under it. Each OU can have its own attribute/value pairs. An OU typically represents a "resource type" or "administrative division". For the "resource" case, "People" (ou=People,dc=example,dc=com) represents one resource of a organization, "Hosts" (ou=Hosts,dc=example,dc=com) is another resource. For the "administrative division" case, the People OU could be further divided in OUs geographically (like ou=EMEA,ou=People,dc=example,dc=com) or divisions of the company (ou=Accounting,ou=People,dc=example,dc=com). OUs may be nested and are limited only by the length of the DN (255 characters).

LDAP searches are done with filters. The filter language is quite extensive: there are tutorials of the LDAP filter language or consult RFC4515. Normally admins do not need to write complicated filters, however, filters used by the apps will be shown in the logs and are useful for debugging.

Note that while LDAP is hierarchical, the data may not be used that way. For example, sys-auth/sssd searches the entire directory for a user. If there are multiple OUs that user, the search will return the union of them all, no matter where in directory they are. On the other hand, when sudo checks LDAP, it restricts is search to its OU.

Warning
An OU cannot be relied on to be a "container". Depending on the search base used the by application - which may be the entire directory - it can return data from multiple OUs. In particular, you cannot have a DN or attribute value that the client expects to be unique (like username or UID) in different OUs under the same search base, even though it's valid and the LDAP server allows it.

LDAP searches are unordered: The server may return the results in whatever order it pleases and need to not be consistent between searches. Sorting must be done by client.

Configuring OpenLDAP

Once OpenLDAP is installed with the correct USE flags, The server must be configured.

Quick Start

Neither the configuration or LDIF files that are bundled in OpenLDAP, or the OpenLDAP Quick Start is suitable for a Gentoo installation Instead, using the following file. Call it slapd.ldif.in

FILE slapd.ldif.in
# Config DN
dn: cn=config
objectClass: olcGlobal
cn: config
# Gentoo locations of files
olcArgsFile: /run/openldap/slapd.args
olcPidFile: /run/openldap/slapd.pid
# Basic logging
olcLogLevel: 768

# Schema DN
dn: cn=schema,cn=config
objectClass: olcSchemaConfig
cn: schema

# Include core schema
include: file:///etc/openldap/schema/core.ldif

# Database frontend DN. Any option listed here affects ALL LDAP databases
dn: olcDatabase=frontend,cn=config
objectClass: olcDatabaseConfig
olcDatabase: frontend

# Config database DN
dn: olcDatabase=config,cn=config
objectClass: olcDatabaseConfig
olcDatabase: config
olcAccess: to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external
 ,cn=auth" manage by * none

# Monitoring database DN
dn: olcDatabase=monitor,cn=config
objectClass: olcDatabaseConfig
olcDatabase: monitor
olcAccess: to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external
 ,cn=auth" read by dn.base="cn=Manager,${MY_DOMAIN_DC}" read by * none

# Database DN for organization directory info
dn: olcDatabase=mdb,cn=config
objectClass: olcDatabaseConfig
objectClass: olcMdbConfig
olcDatabase: mdb
# Default database size. If needed, uncomment and increase.
#olcDbMaxSize: 1073741824
olcSuffix: ${MY_DOMAIN_DC}
olcDbDirectory: /var/lib/openldap-data
olcRootDN: cn=Manager,${MY_DOMAIN_DC}
olcDbIndex: objectClass eq,pres
olcDbIndex: ou,cn,mail,surname,givenname eq,pres,sub
olcAccess: to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external
 ,cn=auth" manage by * break
olcAccess: to attrs=userPassword
  by self write
  by anonymous auth
  by * none
olcAccess: to * 
  by * read
olcLimits: dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth"
  time.soft=unlimited time.hard=unlimited
  size.soft=unlimited size.hard=unlimited

Run the following command, replacing dc=example,dc=com with your director component information.

user $sed s/\${MY_DOMAIN_DC}/dc=example,dc=com/g < slapd.ldif.in > slapd.ldif

Create, populate and set the permissions of the /etc/openldap/slapd.d directory

root #( umask 077 && mkdir /etc/openldap/slapd.d )
root #slapadd -n 0 -l slapd.ldif -F /etc/openldap/slapd.d
root #chown -R ldap:ldap /etc/openldap/slapd.d

Starting the slapd daemon

OpenRC

Edit /etc/conf.d/slapd as follows

FILE /etc/conf.d/slapd(Excerpt)
# Comment this line to disable the old slapd.conf file
#OPTS_CONF="-f /etc/${INSTANCE}/slapd.conf"
# Uncomment this to use the new slapd.d configuration directory
OPTS_CONF="-F /etc/${INSTANCE}/slapd.d"

Note that OpenRC places the ldapi socket file in a nonstandard place. So change any instances of ldapi:/// to ldapi://%2frun%2fopenldap%2fslapd.sock in the subsequent instructions.

Then enable and start the daemon:

root #rc-config add slapd default
root #rc-service slapd start

Systemd

Edit /etc/systemd/system/slapd.service.d/00gentoo.conf as follows:

FILE /etc/systemd/system/slapd.service.d/00gentoo.conf(Excerpt)
# Use the classical configuration file:
#Environment="SLAPD_OPTIONS=-f /etc/openldap/slapd.conf"
# Use the slapd configuration directory:
Environment="SLAPD_OPTIONS=-F /etc/openldap/slapd.d"

Then enable start the daemon:

root #systemctl enable --now slapd

Schemas

One schema is required: the core schema. Without it, no entries can be added to the directory. Additional schema are usually required. Some schema have dependencies on other schemas. In that case, all the schemas to be added must be included in the same LDIF file.

Add a schema

To add a schema, create an LDIF file with an "include: " statement for each schema to be added, along with its dependencies.

For example. the nis schema depends on the cosine schema. So both need to included, starting with the dependencies

FILE addschema.ldif
include: file:///etc/openldap/schema/cosine.ldif

include: file:///etc/openldap/schema/nis.ldif

Then add it to the server

root #ldapadd -H ldapi:/// -Y EXTERNAL -f addschema.ldif
Warning
Schemas cannot be removed while the server is online. Removing schemas usually results in disastrous consequences, so its not something to take lightly!

Convert a .schema file to LDIF

OpenLDAP has supported .ldif file for schemas since version 2.3 (release year 2005). Some programs and packages, however, still do not ship LDIF files and ship .schema files instead. OpenLDAP has a utility to convert them.

A good example is app-admin/sudo. It ships a schema file, not an LDIF file, so it must be converted. To covert:

Create a old-style configuration file that includes the schema. If the schema has dependencies, those must be included before the desired schema in the configuration file.

FILE sudo-schema.conf
include /etc/openldap/schema/sudo.schema

Create an empty directory:

user $mkdir myconfig

Run the slaptest command with the proper arguments:

user $slaptest -f sudo-schema.conf -F myconfig

Look for the LDIF file in the myconfig/cn=config/cn=schema directory. For sudo, this file is called {0}sudo.ldif. Clean up the file and rename it:

user $sed -e '/^#/d' -e '/^dn: /s/$/,cn=schema,cn=config/g' -e 's/{[[:digit:]]*}//g' -e '/^structuralObjectClass/d' -e '/^entryUUID/d' -e '/^creatorsName/d' -e '/^createTimestamp/d' -e '/^entryCSN/d' -e '/^modifiersName/d' -e '/^modifyTimestamp/d' < myconfig/cn\=config/cn\=schema/cn\=\{0\}sudo.ldif > sudo.ldif

The LDIF file may now be added like any other schema.

root #ldapadd -H ldapi:/// -Y EXTERNAL -f sudo.ldif

The temporary files can now be cleaned up:

user $rm -fr myconfig

Modules

Modules extend the functionality of OpenLDAP. There are modules for different backend type (like mdb), encryption algorithms (like argon2) and overlays (like accesslog). Some modules are compiled in, like the back_mdb and syncrepl modules, and (if argon2 is specified), argon2.

For example, to add the password policy module (assuming overlays has been set, create the following LDIF file:

FILE add-module.ldif
dn: cn=module,cn=config
changetype: add
objectClass: olcModuleList
cn: module
olcModulePath: /usr/lib64/openldap/openldap
olcModuleLoad: ppolicy.so

Add the entries to the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f add-module.ldif
Warning
Modules cannot be removed while the server is online. Removing modules usually results in disastrous consequences, so its not something to take lightly!

Security

OpenLDAP supports two popular security solutions: TLS (SSL) and Kerberbos (GSSAPI). Both may be used, if desired.

TLS

A certificate is required to setup TLS. Typically a certificate is obtained either through an in house enterprise certificate authority, or from an external authority, like Let's Encrypt. Since LDAP servers are not usually exposed to the Internet, the former option is preferred.

The TLS server needs the CA certificate, the server certificate, and the key. The certificates and key should be placed /etc/openldap/ssl with the proper permissions (444 for the certificates, 400 for the key). Change ownership of the files to the ldap user and group. The key should not have a password on it.

Create an LDIF file to add the location of the CA certificate, server certificate, and the key. The exmaple below expects the CA certificate at /etc/openldap/ssl/ca.crt, the server certificate at /etc/openldap/ssl/ldap.crt, and they key at /etc/openldap/ssl/ldap.key

FILE ldap-tls.ldif
dn: cn=config
changetype: modify
add: olcTLSCACertificateFile
olcTLSCACertificateFile: /etc/openldap/ssl/ca.crt
-
add: olcTLSCertificateFile
olcTLSCertificateFile: /etc/openldap/ssl/ldap.crt
-
add: olcTLSCertificateKeyFile
olcTLSCertificateKeyFile: /etc/openldap/ssl/ldap.key

Add the entries to the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f ldap-tls.ldif

The LDAP clients must be configured with the certificate of the CA the server's cert in signed with. For each client, copy the CA cert to /etc/openldap/ca.crt and set the permissions to 444. Edit /etc/openldap/ldap.conf and add the following line:

FILE /etc/openldap/ldap.conf
TLS_CACERT /etc/openldap/ca.crt

Kerberos

If OpenLDAP is compiled with Kerberos (and sasl) support, no configuration in OpenLDAP is needed for Kerberos. However, the server has to know where to find its keytab. It cannot use the system keytab because it has the wrong permissions. A special keytab must be created for OpenLDAP. An environmental variable, KRB5_KTNAME must be set in the server's context to find it. Extract the ldap principal for this server (ldap/FQDN@DOMAIN) and save in a keytab to a file called /etc/openldap/krb5-ldap.keytab. Set file ownership to the ldap user and group, and set permissions to 400.

OpenRC

Uncomment the KRB5_KTNAME line

FILE /etc/conf.d/slapd(Excerpt)
# Specify the kerberos keytab file
KRB5_KTNAME=/etc/openldap/krb5-ldap.keytab
Systemd

Edit /etc/systemd/system/slapd.service.d/00gentoo.conf and uncomment the KRB5_KTNAME line.

FILE /etc/systemd/system/slapd.service.d/00gentoo.conf(Excerpt)
# Specify the kerberos keytab file
Environment=KRB5_KTNAME=/etc/openldap/krb5-ldap.keytab

Enforce encryption

TLS and Kerberos allow the server to encrypt communications via the client though STARTTLS, but it do not mandate it. The LDAP server can be configure to force use of encryption:

Create this LDIF:

FILE enforce-encryption.ldif
dn: cn=config
changetype: modify
add: olcLocalSSF
olcLocalSSF: 128

dn: olcDatabase={2}mdb,cn=config
changetype: modify
replace: olcSecurity
olcSecurity: update_ssf=128 simple_bind=1

The first rule for olcLocalSSF protects against locking out local access. The value must be at least are large as the largest value in olcSecurity. The example above requires encryption to update any entries, but only integrity protection to bind. This is only relevant for Kerberos: if the SSF is not 0, all TLS implementation will always encrypt (and most Kerberos ones will too).

Add the entries to the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f enforce-encryption.ldif
Warning
Do not specify tls=1 in olcSecurity, otherwise, local users and non-TLS Kerberos users will be locked out

For increased flexibility, access control rules can be used in addition to, or instead of, mandating security via olcSecurity.

Access Control

Each database has it own access control. The default for the directory databases (like mdb) is to grant read to all, otherwise, the default is no access to anyone. See Access Control via Dynamic Configuration for the syntax and examples.

An example access control configuration:

FILE access-control.ldif
dn: olcDatabase={2}mdb,cn=config
changetype: modify
replace: olcAccess
olcAccess: to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external
 ,cn=auth" manage by * break
olcAccess: to attrs=userPassword
  by ssf=128 self write 
  by anonymous auth
  by * none
olcAccess: to * 
  by users read
  by * none

The above example allows local root to manage the database, requires encryption when updating the passwords, allows authenticated users read and denies everyone else access. Note the by * break in the first rule OpenLDAP normally stops at the first matching rule, and if the entity isn't matched in that rule, access is denied without further evaluating any other rules - unless the break rule is specified.

Limits

For large directories, an LDAP query can take significant resources (time and bandwidth). Server-side limits on query can be enforced. See Limits for syntax and examples. There are version of the limit: soft and hard. The soft limit is the maximum resources used if the client doesn't specify a limit. This is works as a default value for clients. The hard limit is the maximum resources the client can request if they do specify a limit. Either or both may be specified in a limit rule. The 2 main resources that can be constrained by limits is size and time

An example limit configuration:

FILE limit-control.ldif
dn: olcDatabase={2}mdb,cn=config
changetype: modify
replace: olcLimits
olcLimits: dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth"
  time.soft=unlimited time.hard=unlimited
  size.soft=unlimited size.hard=unlimited
olcLimits: dn.exact="cn=replicator,dc=example,dc=com"               
  time.soft=unlimited time.hard=unlimited
  size.soft=unlimited size.hard=unlimited
olcLimits: users
  time=3600
  size=1000
olcLimits: *
  time.soft=15 time.hard=60
  size.soft=10 size.hard=100

Thew above example gives the local root and replicator users no limits, both hard and soft limits of 3600 seconds and 1000 results per query, and everyone else (like anonymous users) gets a soft limit of 15 seconds and 10 results per query, and a hard limit of 60 seconds an 100 results per query.

Remote RootDN access

The quick start creates a RootDN that can access anything, however, the RootPW is not set, meaning the RootDN cannot login. The RootPW must be set to login:

FILE ldap-rootpw.ldif
dn: olcDatabase={2}mdb,cn=config
changetype: modify
add: olcRootPW
# Use a better password than this!
olcRootPW: secret

Add the entries to the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f ldap-rootpw.ldif

When proper access has been set up, remove the root password:

root #ldapmodify -H ldapi:/// -Y EXTERNAL
dn: olcDatabase={2}mdb,cn=config
changetype: modify 
delete: olcRootPW

Replication

LDAP uses a push/pull model for replication. The "pusher" is called the producer and the "puller" is called the consumer. A server can have both roles (servers that only consume would need to be read-only and forward writes via referrals). There are 2 sync protocols: syncrepl and delta-syncrepl. The former sends all attributes of a DN that has changed, the latter sends only the attributes of the DN that changed. delta-Syncrepl uses less traffic but requires more configuration.

The number of replication scenarios are limited only by the imagination. See Replication in the documentation for some examples. Two will be covered here: Mirrors and Read-only replicas.

Replication considerations

The replication process requires a Bind DN and secret. The Bind DN must have read access to the entire database and not be subject to limits in order to complete its work. Also, unlike the userPassword attribute, the secret must be in the clear. Therefore, the use of TLS is critical.

So there's 3 options for replication authentication

  1. Use the RootDN
  2. Use a dedicated replication account
  3. Do something fancy with Kerberos/SASL

Option 1 is the easiest, but least secure.

For option 2, a dedicated replicator DN can created (Note the database need to be populated first: #Populating the directory):

FILE replicator.ldif.in
dn: cn=replicator,${MY_DOMAIN_DC}
changetype: add
objectClass: simpleSecurityObject
objectClass: organizationalRole
cn: replicator
description: Replication user
userPassword: {CRYPT}x

dn: olcDatabase={2}mdb,cn=config
changetype: modify
replace: olcAccess
olcAccess: to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external
 ,cn=auth" manage
  by dn.exact="cn=replicator,${MY_DOMAIN_DC}" read
  by * break
olcAccess: to attrs=userPassword
  by self write
  by anonymous auth
  by * none
olcAccess: to *
  by * read
-
replace: olcLimits
olcLimits: dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth"
  time.soft=unlimited time.hard=unlimited
  size.soft=unlimited size.hard=unlimited
olcLimits: dn.exact="cn=replicator,${MY_DOMAIN_DC}"               
  time.soft=unlimited time.hard=unlimited
  size.soft=unlimited size.hard=unlimited

The above olcAccess rules assumes the quick start configuration is in use. If a different configuration is in use, make sure the olcAccess rule giving the replicator user read access is in the first rule, and don't forget the by * break to continue evaluating the access control rules for other entities.

Use sed to fill in the blanks, replacing dc=example,dc=com with your directory component information.

user $sed -e 's/${MY_DOMAIN_DC}/dc=example,dc=com/g' < replicator.ldif.in > replicator.ldif

Add it to the server

root #ldapmodify -c -H ldapi:/// -Y EXTERNAL -f replicator.ldif

Change the password (substitute your DC)

root #ldappasswd -H ldapi:// -Y EXTERNAL -S cn=replicator,dc=example,dc=com

For option 3, this requires something like Kerberos (GSSAPI) or client certificates (TLS with EXTERNAL). This is the most difficult option. Figuring out how to set this up is a exercise for the reader.

Preparing the producer for delta-syncrepl (Optional)

The producer OpenLDAP must have been built with the overlay flag. The producer also needs the accesslog module loaded:

FILE mod-accesslog.ldif
dn: cn=module,cn=config
changetype: add
objectClass: olcModuleList
cn: module
olcModulePath: /usr/lib64/openldap/openldap
olcModuleLoad: accesslog.so

Add the entries to the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f mod-accesslog.ldif

Create the directories for the access log and fix the owner:

root #( umask 077 && mkdir /var/lib/openldap-data/accesslog )
root #chown -R ldap:ldap /var/lib/openldap-data/accesslog

Next, another database needs to be created, along with a syncrepl overlay for it. The accesslog over is also added to the main database:

FILE deltasync-producer.ldif
dn: olcDatabase=mdb,cn=config
changetype: add
objectClass: olcDatabaseConfig
objectClass: olcMdbConfig
olcDatabase: mdb
olcDbDirectory: /var/lib/openldap-data/accesslog
olcSuffix: cn=accesslog
olcDbIndex: default eq
olcDbIndex: entryCSN,objectClass,reqEnd,reqResult,reqStart,reqDN
olcAccess: to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external
 ,cn=auth" manage
# Delete this comment and uncomment the next lines if a dedicated replicator account is in use
#  by dn.exact="cn=replicator,dc=example,dc=com" read
#olcLimits: dn.exact="cn=replicator,dc=example,dc=com"
#  time.soft=unlimited time.hard=unlimited
#  size.soft=unlimited size.hard=unlimited

dn: olcOverlay=syncprov,olcDatabase={3}mdb,cn=config
changetype: add
objectClass: olcOverlayConfig
objectClass: olcSyncProvConfig
olcOverlay: syncprov
olcSpNoPresent: TRUE
olcSpReloadHint: TRUE

dn: olcOverlay=accesslog,olcDatabase={2}mdb,cn=config
changetype: add
objectClass: olcOverlayConfig
objectCLass: olcAccessLogConfig
olcOverlay: accesslog
olcAccessLogDB: cn=accesslog
olcAccessLogOps: writes
olcAccessLogSuccess: TRUE
# Scan the data once a day and purge anything older than a week
olcAccessLogPurge: 07+00:00 01+00:00

Add the entries to the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f deltasync-producer.ldif

Mirroring configuration

Since each server is both a producer and consumer, the configuration is almost exactly the same for each.

First, the producer part. Configure the Server ID and an LDAP overlay:

FILE mirror-producer.ldif.in
dn: cn=config
changetype: modify
add: olcServerID
# An arbitrary, unique 3 digit hexadecimal value 
olcServerID: ${MY_SERVER_ID} ldap://${MY_SERVER_NAME}

dn: olcDatabase={2}mdb,cn=config
changetype: modify
add: olcDbIndex
olcDbIndex: entryCSN,entryUUID eq
# If the quick start configuration wasn't used, this may be required too
# olcDbIndex: objectClass eq

dn: olcOverlay=syncprov,olcDatabase={2}mdb,cn=config
changetype: add
objectClass: olcOverlayConfig
objectClass: olcSyncProvConfig
olcOverlay: syncprov
olcSpCheckpoint: 100 10
olcSpSessionlog: 100

Use sed to fill in the blanks, substituting 001 with desired server ID, and ldap1.example.com with the producer's LDAP FQDN.

user $sed -e 's/${MY_SERVER_ID}/001/g' -e 's/${MY_SERVER_NAME}/ldap1.example.com/g' < mirror-producer.ldif.in > mirror-producer.ldif

Add the entries to the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f mirror-producer.ldif

Second, the consumer part. Configure replication:

FILE mirror-consumer.ldif.in
dn: olcDatabase={2}mdb,cn=config
changetype: modify
add: olcSyncrepl
# The RID value is arbitrary
olcSyncrepl: rid=001
  provider=ldap://${MY_SERVER_NAME}
  searchbase="${MY_DOMAIN_DC}"
  bindmethod=simple
  binddn="cn=replicator,${MY_DOMAIN_DC}"
  credentials=secret
  type=refreshAndPersist
  retry="60 +"
  starttls=critical
# Delete this comment and uncomment out the next 2 lines if using delta-syncrepl
#  logbase="cn=accesslog"
#  logfilter="(&(objectClass=auditWriteObject)(reqResult=0))"
-
add: olcMultiProvider
olcMultiProvider: TRUE

Use sed to fill in the blanks, replacing dc=example,dc=com with your directory component information, and ldap.example.com with the producer's LDAP FQDN.

user $sed -e 's/${MY_SERVER_NAME}/ldap2.example.com/g' -e 's/${MY_DOMAIN_DC}/dc=example,dc=com/g' < mirror-consumer.ldif.in > mirror-consumer.ldif

If using delta-syncrepl, follow the instructions in the LDIF file. Also, substitute the values of binddn and credentials with the correct values. Load it onto the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f mirror-consumer.ldif

Then repeat for the other server, choosing a new olcServerID and swapping the URLs for the producer and consumer.

It is possible to extend this to multiple mirrors, such a configuration is called "N-Way Multi-Provider Replication". Its basically the same as mirroring, except there's multiple olcSyncrepl entries - one of each other server.

Read-only replicas configuration

On the producer configure as follows:

FILE producer.ldif.in
dn: cn=config
changetype: modify
add: olcServerID
# An arbitrary, unique 3 digit hexadecimal value 
olcServerID: ${MY_SERVER_ID} ldap://${MY_SERVER_NAME}

dn: olcDatabase={2}mdb,cn=config
changetype: modify
add: olcDbIndex
olcDbIndex: entryCSN,entryUUID eq
# If the quick start configuration wasn't used, this may be required too
# olcDbIndex: objectClass eq

dn: olcOverlay=syncprov,olcDatabase={2}mdb,cn=config
changetype: add
objectClass: olcOverlayConfig
objectClass: olcSyncProvConfig
olcOverlay: syncprov
olcSpCheckpoint: 100 10
olcSpSessionlog: 100

Use sed to fill in the blanks, substituting 001 with desired server ID, and ldap1.example.com with the producer's LDAP FQDN.

user $sed -e 's/${MY_SERVER_ID}/001/g' -e 's/${MY_SERVER_NAME}/ldap1.example.com/g' < producer.ldif.in > producer.ldif

Add the entries to the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f producer.ldif

On the consumers, configure as follows:

FILE consumer.ldif.in
dn: olcDatabase={2}mdb,cn=config
changetype: modify
add: olcSyncrepl
# The RID value is arbitrary
olcSyncrepl: rid=001
  provider=ldap://${MY_SERVER_NAME}
  searchbase="${MY_DOMAIN_DC}"
  bindmethod=simple
  binddn="cn=replicator,${MY_DOMAIN_DC}"
  credentials=secret
  type=refreshAndPersist
  retry="60 +"
  starttls=critical
# Delete this comment and uncomment out the next 2 lines if using delta-syncrepl
#  logbase="cn=accesslog"
#  logfilter="(&(objectClass=auditWriteObject)(reqResult=0))"
-
add: olcUpdateRef
olcUpdateRef: ldap://${MY_SERVER_NAME}

Use sed to fill in the blanks, replacing dc=example,dc=com with your directory component information, and ldap.example.com with the producer's LDAP FQDN.

user $sed -e 's/${MY_SERVER_NAME}/ldap.example.com/g' -e 's/${MY_DOMAIN_DC}/dc=example,dc=com/g' < consumer.ldif.in > consumer.ldif

If using delta-syncrepl, follow the instructions in the LDIF file. Also, substitute the values of binddn and credentials with the correct values. Load it onto the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f consumer.ldif

This is almost the same as mirroring, but without the olcMultiProvider entry and with an added olcUpdateRef for the database.

Populating the directory

Unless the server is a replication consumer of an already populated producer, the directory itself is still empty. The initial entry must be created or imported:

Populating the directory via creation

FILE populate.ldif.in
dn: ${MY_DOMAIN_DC}
changetype: add
objectClass: dcObject
objectClass: organization
o: TO FILLED IN BY LDAP ADMIN
dc: ${MY_DOMAIN}

dn: cn=Manager,${MY_DOMAIN_DC}
changetype: add
objectClass: organizationalRole
cn: Manager

Use sed to fill in the blanks, replacing dc=example,dc=com with your directory component information and example with the first part of the domain name.

user $sed -e 's/${MY_DOMAIN_DC}/dc=example,dc=com/g' -e 's/${MY_DOMAIN}/example/g' < populate.ldif.in > populate.ldif

Don't forget the change the value of the o attribute to something suitable (either the name of the organization, or the FQDN of the domain if nothing in particular is suitable). Load it onto the server:

root #ldapmodify -H ldapi:/// -Y EXTERNAL -f populate.ldif

Once the initial population is done, the directory can be loaded with data.

Populating the directory via import

The old directory needs to be exported with all the internal attributes. For OpenLDAP, the slapcat command on the old server will produce a suitable output. Copy the LDIF file to the new server, shut down OpenLDAP if it's still running, and import the old database with slapadd. The database ownership will need to be updated:

root #chown -R ldap:ldap /var/lib/openldap-data

Then start up OpenLDAP.

Adminstration

Backing up the database

To backup the database, use slapcat on the main database (if delta-syncrepl is in use, backup the accesslog database as well). Typically this would be run by a cron jon or systemd timer. The backup should be considered sensitive.

Clearing all schemas

Removing schemas is not a simple task. Slapd must be offline and the unwanted schemas must be removed with slapmodify using a delete operation. Sometimes OpenLDAP will refuse to do so. Because the config files should never be changed manually, the best way to continue is to delete all schemas and then re-add the desired ones. To do that, slapcat can be used to produce a filtered LDIF, then the LDIF manually edited to re-include the desired schemas.

With slapd offline, issue the following slapcat command:

root #slapcat -n 0 -H 'ldap:///???(!(entryDN:dnSubtreeMatch:=cn=schema,cn=config))' > new_schemas.ldif

Insert the following blocks after the first cn=config block

FILE new_schemas.ldif(Insert after first cn=config block)
dn: cn=schema,cn=config
objectClass: olcSchemaConfig
cn: schema

# Required. Note there should be a blank line before and after every include statement
include: file:///etc/openldap/schema/core.ldif

# Include schema dependencies first then the desired schema
include: file:///etc/openldap/schema/cosine.ldif

include: file:///etc/openldap/schema/nis.ldif

Backup the old directory, create a new empty config directory and add the new LDIF configuration:

root #mv /etc/openldap/slapd.d/ /etc/openldap/slapd.d.old
root #( umask 077 && mkdir /etc/openldap/slapd.d )
root #slapadd -n 0 -l new_schemas.ldif -F /etc/openldap/slapd.d
root #chown -R ldap:ldap /etc/openldap/slapd.d
root #slaptest
root #slapschema -n 2

If slaptest fails be sure the file above was inserted in the to correct place and the required newlines are there. If slapschema fails, either add the missing schema. If the schema is to be decommsioned, the incompatible attributes will have to be removed from the directory. The server might not start until the problem is fixed; at the very least the DNs with attributes without a schema will be inaccessible.

Open file limits

By default, processes are soft limited to 1024 descriptors, and hard limited to 4096 descriptors. If slapd starts showing the "Too many open files" message, the limit has been exceeded. Increasing the limit depends on the init system:

OpenRC

start-stop-daemon sets the limits for the process using the user listed in pam_limits. Either edit /etc/security/pam_limits.conf or add a file in the /etc/security/limits.d directory with the following lines, replacing 8192 with the desired value:

FILE /etc/security/pam_limits.conf
ldap           soft    nofile          8192
ldap           hard    nofile          8192

Slapd must be restarted for changes to take effect:

root #rc-service slapd restart

Systemd

Systemd itself controls the limits of service, and the limits can be increased by editing the config file. Append the following /etc/systemd/system/slapd.service.d/00gentoo.conf, replacing 8192 with the desired value:

FILE /etc/security/pam_limits.conf
[Service]
LimitNOFILE=8192

Slapd must be restarted for changes to take effect:

root #systemctl restart slapd

Troubleshooting

Turning up the log level

To turn up the log level, change the value of olcLogLevel. The admin guide lists the possible values

root #ldapmodify -H ldapi:/// -Y EXTERNAL
dn: cn=config
changetype: modify
replace: olcLogLevel
olcLogLevel: 1023

Once the problem has been fixed. it can changed back to 768 using the above construction.

See also