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# OpenLDAP

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OpenLDAP is an open-source implementation of the LDAP protocol. An LDAP server basically is a non-relational database which is optimised for accessing, but not writing, data. It is mainly used as an address book (for e.g. email clients) or authentication backend to various services (such as Samba, where it is used to emulate a domain controller, or Linux system authentication, where it replaces `/etc/passwd`) and basically holds the user data.

Note: Commands related to OpenLDAP that begin with `ldap` (like `ldapsearch`) are client-side utilities, while commands that begin with `slap` (like `slapcat`) are server-side.

This page is a starting point for a basic OpenLDAP installation and a sanity check.

Tip: Directory services are an enormous topic. Configuration can therefore be complex. If you are totally new to those concepts, this is a good introduction that is easy to understand and that will get you started, even if you are new to LDAP.

## Installation

OpenLDAP contains both a LDAP server and client. Install it with the package openldap.

## Configuration

### The server

Note:

- If you have an obsolete `slapd.conf` configuration, you can simply convert it into the new `cn=config` database using

    $ slaptest -f /etc/openldap/slapd.conf -F /etc/openldap/slapd.d/

- If you already have an OpenLDAP database on your machine and would like to remove it, then it can be removed by deleting everything inside of `/var/lib/openldap/openldap-data/`. So, backup your `DB_CONFIG`.

Slapd, the server, stores its configuration directly inside its database. Thus, we need to write our configuration as an LDIF file and import it.

First, create the directory `/var/lib/openldap/openldap-data/`, where your LDAP database contents ("database 1", as OpenLDAP calls it):

    # install -m 0700 -o ldap -g ldap -d /var/lib/openldap/openldap-data/

Now we need to create a place for the LDAP configuration database ("database 0"):

    # install -m 0760 -o root -g ldap -d /etc/openldap/slapd.d

Create a file `/etc/openldap/config.ldif` containing the following minimal useful configuration:

    /etc/openldap/config.ldif

    # The root config entry
    dn: cn=config
    objectClass: olcGlobal
    cn: config
    olcArgsFile: /run/openldap/slapd.args
    olcPidFile: /run/openldap/slapd.pid

    # Schemas
    dn: cn=schema,cn=config
    objectClass: olcSchemaConfig
    cn: schema

    # TODO: Include further schemas as necessary
    include: file:///etc/openldap/schema/core.ldif

    # The config database
    dn: olcDatabase=config,cn=config
    objectClass: olcDatabaseConfig
    olcDatabase: config
    olcRootDN: cn=Manager,$BASEDN

    # The database for our entries
    dn: olcDatabase=mdb,cn=config
    objectClass: olcDatabaseConfig
    objectClass: olcMdbConfig
    olcDatabase: mdb
    olcSuffix: $BASEDN
    olcRootDN: cn=Manager,$BASEDN
    olcRootPW: $PASSWD
    olcDbDirectory: /var/lib/openldap/openldap-data
    # TODO: Create further indexes
    olcDbIndex: objectClass eq

There are a few options you will need to change:

- Every occurence of `$BASEDN` must be replaced with a valid DN. If you own a domain `example.com` you will most likely want to choose `dc=example,dc=com`.
- `$PASSWD` must be replaced by a salted and hashed password, which you may generate by running `slappasswd`.

Additionally, you might consider to add further schemas and create additional indexes to tune the performance of your database. The specifics will depend on your use case, but here are a few recommendations. For LDAP authentication, you should include the three schemas below to be able to use the `posixAccount` object class used for storing users.

Note: Additional indexes must be part of the preceeding block. Newlines will result in a corrupted configuration file

    # TODO: Create further indexes
    olcDbIndex: objectClass eq
    olcDbIndex: uid pres,eq
    olcDbIndex: mail pres,sub,eq
    olcDbIndex: cn,sn pres,sub,eq
    olcDbIndex: dc eq

    # Additional schemas
    # RFC1274: Cosine and Internet X.500 schema
    include: file:///etc/openldap/schema/cosine.ldif
    # RFC2307: An Approach for Using LDAP as a Network Information Service
    # Check RFC2307bis for nested groups and an auxiliary posixGroup objectClass (way easier)
    include: file:///etc/openldap/schema/nis.ldif
    # RFC2798: Internet Organizational Person
    include: file:///etc/openldap/schema/inetorgperson.ldif

Allow logins to the `ldap` user account with `chsh`, typically selecting the shell `/bin/bash`. Then import these settings as the `ldap` user:

    [ldap]$ slapadd -n 0 -F /etc/openldap/slapd.d/ -l /etc/openldap/config.ldif

Alternatively, you may also run this directly as `root`. However, if you do, make sure `/etc/openldap/slapd.d/` remains accessible by `ldap`:

    # slapadd -n 0 -F /etc/openldap/slapd.d/ -l /etc/openldap/config.ldif
    # chown -R ldap:ldap /etc/openldap/*

If everything worked, you will now have directories underneath `/etc/openldap/slapd.d` with names such as `cn=config`.

By default, OpenLDAP will listen unencrypted on all interfaces. To make it only listen on local IP interfaces, you may edit the environment file read by `slapd.service`:

    /etc/conf.d/slapd

    SLAPD_URLS="ldap://127.0.0.1/ ldap://[::1]"
    SLAPD_OPTIONS=

Finally, start the slapd daemon by starting `slapd.service`.

Note:

- If you want to have your directory accept requests from the network, you should consider using TLS. See #OpenLDAP over TLS for details.
- If you plan to use your LDAP server for authentication, you might want to check access control configuration in LDAP authentication#LDAP server setup.
- Berkeley DB (BDB) should no longer be used. The mdb backend to slapd(8) is the recommended primary backend for a normal slapd database. It uses OpenLDAP's own Lightning Memory-Mapped Database (LMDB) library to store data and is intended to replace the Berkeley DB backend. The OpenLDAP package in the official repositories defaults to mdb.

### The client

The client configuration file is located at `/etc/openldap/ldap.conf`.

It is quite simple: you will only have to alter `BASE` to reflect the suffix of the server, and `URI` to reflect the address of the server, like:

    /etc/openldap/ldap.conf

    BASE            dc=example,dc=com
    URI             ldap://localhost

If you decide to use SSL:

- The protocol (ldap or ldaps) in the `URI` entry has to conform with the slapd configuration
- If you decide to use TLS, add a `TLS_REQCERT allow` line to `ldap.conf`
- If you use a signed certificate from a CA, add the line `TLS_CACERTDIR /usr/share/ca-certificates/trust-source` in `ldap.conf`.

### Create initial entry

Note: If you plan to use your LDAP server for authentication, you should import the `base.ldif` in the LDAP authentication article instead of following the instructions here.

Once your client is configured, you probably want to create the root entry, and an entry for the Manager role:

    $ ldapadd -x -D 'cn=Manager,dc=example,dc=com' -W
    dn: dc=example,dc=com
    objectClass: dcObject
    objectClass: organization
    dc: example
    o: Example
    description: Example directory

    dn: cn=Manager,dc=example,dc=com
    objectClass: organizationalRole
    cn: Manager
    description: Directory Manager
    ^D

The text after the first line is entered on stdin, or could be read from a file either with the `-f` option or a file redirect.

### Test your new OpenLDAP installation

This is easy, just run the command below:

    $ ldapsearch -x '(objectclass=*)' -b 'dc=example,dc=com'

Or authenticating as the rootdn (replacing `-x` by `-D user -W`), using the example configuration we had above:

    $ ldapsearch -D "cn=Manager,dc=example,dc=com" -W '(objectclass=*)' -b 'dc=example,dc=com'

Now you should see some information about your database.

### OpenLDAP over TLS

Note: upstream documentation is much more useful/complete than this section

If you access the OpenLDAP server over the network and especially if you have sensitive data stored on the server you run the risk of someone sniffing your data which is sent clear-text. The next part will guide you on how to setup an SSL connection between the LDAP server and the client so the data will be sent encrypted.

In order to use TLS, you must have a certificate. For testing purposes, a self-signed certificate will suffice. To learn more about certificates, see OpenSSL.

Warning: OpenLDAP cannot use a certificate that has a password associated to it.

#### Create a self-signed certificate

To create a self-signed certificate, type the following:

    $ openssl req -new -x509 -nodes -out slapdcert.pem -keyout slapdkey.pem -days 365

You will be prompted for information about your LDAP server. Much of the information can be left blank. The most important information is the common name. This must be set to the DNS name of your LDAP server. If your LDAP server's IP address resolves to example.org but its server certificate shows a CN of bad.example.org, LDAP clients will reject the certificate and will be unable to negotiate TLS connections (apparently the results are wholly unpredictable).

Now that the certificate files have been created copy them to `/etc/openldap/ssl/` (create this directory if it does not exist) and secure them. `slapdcert.pem` must be world readable because it contains the public key. `slapdkey.pem` on the other hand should only be readable for the ldap user for security reasons:

    # mv slapdcert.pem slapdkey.pem /etc/openldap/ssl/
    # chmod -R 755 /etc/openldap/ssl/
    # chmod 400 /etc/openldap/ssl/slapdkey.pem
    # chmod 444 /etc/openldap/ssl/slapdcert.pem
    # chown ldap /etc/openldap/ssl/slapdkey.pem

#### Configure slapd for SSL

Edit the configuration to tell LDAP where the certificate files reside by executing the following command:

Note: The latest version of OpenLDAP (2.4.45) uses OpenSSL and not GnuTLS. This means that current versions of OpenLDAP do in fact know how to handle the DEFAULT TLSCipherSuite. To prove this one could run `ldd /usr/bin/slapd`.

    ldapmodify -D 'cn=Manager,dc=example,dc=com' -W

    dn: cn=config
    add: olcTLSCertificateFile
    olcTLSCertificateFile: /etc/openldap/ssl/slapdcert.pem
    -
    add: olcTLSCertificateKeyFile
    olcTLSCertificateKeyFile: /etc/openldap/ssl/slapdkey.pem

If you are using a signed SSL Certificate from a certification authority such as Let’s Encrypt, you will also need to specify the path to the root certificates database and your intermediary certificate. You will also need to change ownership of the .pem files and intermediary directories to make them readable to the user `ldap`:

    ldapmodify -D 'cn=Manager,dc=example,dc=com' -W

    dn: cn=config
    add: olcTLSCACertificateFile
    olcTLSCACertificateFile: /etc/letsencrypt/live/ldap.my-domain.com/chain.pem
    -
    add: olcTLSCertificateFile
    olcTLSCertificateFile: /etc/letsencrypt/live/ldap.my-domain.com/cert.pem
    -
    add: olcTLSCertificateKeyFile
    olcTLSCertificateKeyFile: /etc/letsencrypt/live/ldap.my-domain.com/privkey.pem
    -
    add: olcTLSCACertificatePath
    olcTLSCACertificatePath: /usr/share/ca-certificates/trust-source

SSLv2/v3

Disable SSLv2/v3 and use strong ciphers.

    ldapmodify -D 'cn=Manager,dc=example,dc=com' -W

    dn: cn=config
    add: olcTLSProtocolMin
    olcTLSProtocolMin: 3.3
    -
    add: olcTLSCipherSuite
    olcTLSCipherSuite: DEFAULT:!kRSA:!kDHE
    -

TLSProtocolMin specifies the minimum version in wire format, so "3.3" actually means TLSv1.2.

The TLSCipherSuite specifies a list of OpenSSL ciphers from which slapd will choose when negotiating TLS connections, in decreasing order of preference. In addition to those specific ciphers, you can use any of the wildcards supported by OpenSSL. Note: DEFAULT is a wildcard. See ciphers(1ssl) for description of ciphers, wildcards and options supported.

Note: To see which ciphers are supported by your local OpenSSL installation, type the following: `openssl ciphers -v ALL:COMPLEMENTOFALL`. Always test which ciphers will actually be enabled by TLSCipherSuite by providing it to OpenSSL command, like this: `openssl ciphers -v 'DEFAULT'`.

#### Start slapd with SSL

Note: This is not needed for StartTLS which listens on the same port as unencrypted LDAP.

You will have to edit the environment file read by `slapd.service` to change the protocol slapd listens on:

    /etc/conf.d/slapd

    SLAPD_URLS="ldaps:///"
    SLAPD_OPTIONS=

Localhost connections do not need to use SSL. So, if you want to access the server locally you should change the `SLAPD_URLS` line to:

    SLAPD_URLS="ldap://127.0.0.1 ldaps:///"

Then restart `slapd.service`. If it was enabled before, reenable it now.

Note: If you created a self-signed certificate above, be sure to add `TLS_REQCERT allow` to `/etc/openldap/ldap.conf` on the client, or it will not be able connect to the server.

## Next steps

You now have a basic LDAP installation. The next step is to design your directory. The design is heavily dependent on what you are using it for. If you are new to LDAP, consider starting with a directory design recommended by the specific client services that will use the directory (PAM, Postfix, etc).

A directory for system authentication is the LDAP authentication article.

A nice web frontend is phpLDAPadmin.

### Backup LDAP

It is imperative that we have a backup of our LDAP database and configuration in case we ever need to restore for any number of reasons.

#### Export configuration

    [ldap]$ slapcat -vF /etc/openldap/slapd.d -n 0 -l "$(hostname)-ldap-mdb-config-$(date '+%F').ldif"

#### Export database

    [ldap]$ slapcat -v -n 1 -l "$(hostname)-ldap-database-$(date '+%F').ldif"

### Restore LDAP

#### Import configuration

    [ldap]$ slapadd -v -n 0 -F /etc/openldap/slapd.d -l <filename from config export>

#### Import database

    [ldap]$ slapadd -v -n 1 -F /etc/openldap/slapd.d -l <filename from database export>

## Troubleshooting

### slapd configuration checking

You can check configuration settings with

    $ slaptest -F /etc/openldap/slapd.d/ -v

### Client authentication checking

If you cannot connect to your server for non-secure authentication:

    $ ldapsearch -x -H ldap://ldaservername:389 -D cn=Manager,dc=example,dc=exampledomain

and for TLS secured authentication with:

    $ ldapsearch -x -H ldaps://ldaservername:636 -D cn=Manager,dc=example,dc=exampledomain

### LDAP server stops suddenly

If you notice that slapd seems to start but then stops, try running:

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

to allow slapd write access to its data directory as the user "ldap".

### LDAP server does not start

Try starting the server from the command line with debugging output enabled:

    # slapd -u ldap -g ldap -h ldaps://ldaservername:636 -d Config,Stats

## See also

- Official OpenLDAP Software Administrator's Guide
- phpLDAPadmin is a web interface tool in the style of phpMyAdmin.
- LDAP authentication
- apachedirectorystudioAUR from the Arch User Repository is an Eclipse-based LDAP viewer. Works perfect with OpenLDAP installations.

Category:

- Directory services