Installing OpenLDAP from Source on CentOS 7

This guide will walk you through installing OpenLDAP from source on CentOS 7. It should work with Red Hat Enterprise Linux (RHEL) 7, Oracle Linux 7, Scientific Linux 7, and any other RHEL clones. I am assuming you are able to use a command line shell and text editor on a UNIX like operating system. This guide was tested on OpenLDAP 2.4.47. All of the examples use this version as well.

I recommend installing OpenLDAP from source instead of the package manager to ensure you get the latest bug and security fixes, you have the features you need, and to ensure it is built the same way when you update. I had an experience where I installed OpenLDAP from an OS repository, updated it from the repository, and found the TLS library it was built with had been changed! This caused the server daemon to not start. Fortunately, it was part of a cluster, so it didn’t cause a service outage.

Get to Know the Official Documentation

I recommend getting familiar with the official documentation of any software you use. The official administrator’s guide covers the software pretty well, so take a few minutes to browse through the table of contents before getting started. I also recommending skimming through the quick start guide and the building and installing chapter of the administrator’s guide. Note that at the end of the administrator’s guide, there is a list of links to various Internet Engineering Task Force Requests For Comments specifying various standards applicable to OpenLDAP. It wouldn’t hurt to take a few minutes to browse through these and read the abstracts if you aren’t well versed with LDAP and directory servers. If you want to get a better understanding of how X.500 directories structure their data, RFC 4512 would be a good place to start.

Preparation

There isn’t much preparation other than obtaining the source and installing a few packages. Set a few environment variables to save some typing. I am assuming you are using bash since it is the default shell on CentOS 7. All of the commands in this guide should be executed as root. Create the file /root/.ldap-env with the following contents:

export PATH=/opt/openldap-current/bin:/opt/openldap-current/sbin:/opt/openldap-current/libexec:$PATH
export OWNER=ldap:ldap
export CONFIG=/opt/openldap-current/etc/openldap/slapd.d

Now source the file:

source /root/.ldap-env

Source this file whenever you will be working with your OpenLDAP installation. I would consider adding it to your login and/or invocation scripts.

Download the source to your system. On the download page, you have to use the release link on the right column of the table. If you prefer, the following command will download the latest version as of 2019, April 6.

curl "ftp://ftp.openldap.org/pub/OpenLDAP/openldap-release/openldap-2.4.47.tgz" > openldap-2.4.47.tgz

Install the packages that you will need to compile the source. Use the following command:

yum install make gcc openssl-devel libtool-ltdl-devel libdb-devel cyrus-sasl-devel

Configuring and Compiling

Extract the source tar file:

tar xf openldap-2.4.47.tgz 
cd openldap-2.4.47

Configure the source. I am assuming you will be using MDB to store your data. If there is any interest in using some of the other options, such as perl or an RDBMS, send a message through the contact page. Using these options will require additional OS packages and configure script options.

./configure --with-cyrus-sasl --with-tls=openssl --enable-overlays=mod \
    --enable-backends=mod --disable-perl --disable-ndb --enable-crypt \
    --enable-modules --enable-dynamic --enable-syslog --enable-debug --enable-local \
    --enable-spasswd --disable-sql --prefix=/opt/openldap-2.4.47

Compile the source:

make depend
make
cd contrib/slapd-modules/passwd/sha2
make
cd ../../../..

Now run the test suite to make sure everything went ok. It should take roughly an hour depending on your hardware.

make test > test_results.txt
grep '>>>>>.*failed' test_results.txt

If any of the tests fail, I advise fixing whatever went wrong before proceeding, especially in a production environment.

Installing the Software

By default, OpenLDAP stores passwords as salted SHA-1 hashes. Since SHA-1 is no longer considered secure, I have included instructions on how to install a module that will enable OpenLDAP to use SHA-2 hashes. To save the trouble of messing with your systemd unit file and directory configuration after an upgrade, we will create a symbolic link to the installation directory.

make install
cd contrib/slapd-modules/passwd/sha2
make DESTDIR=/opt/openldap-2.4.47 install
../../../../libtool --finish /opt/openldap-2.4.47/usr/local/libexec/openldap
cd  /opt/openldap-2.4.47/usr/local/libexec/openldap
mv * /opt/openldap-2.4.47/libexec/openldap

Create the server’s user and group. The commands below will create the same user and group as the package manager would if you were to install the OpenLDAP server from the repositories.

groupadd -g 55 ldap
useradd  -g 55 -u 55 -s /sbin/nologin -d /var/lib/ldap -c "OpenLDAP server" ldap

Fix the permissions on a few directories:

cd /opt/openldap-2.4.47
find . -type d -exec chmod 755 {} \;
cd var/run/
chown $OWNER .

Create a symbolic link that points to the version of OpenLDAP you are currently using:

ln -s /opt/openldap-2.4.47 /opt/openldap-current

Create a service unit file so systemd can start and stop the server on boot and shutdown. Paste the following into the file /etc/systemd/system/slapd-current.service.

[Unit]
Description=OpenLDAP Server Daemon
After=syslog.target network-online.target

[Service]
Type=forking
PIDFile=/opt/openldap-current/var/run/slapd.pid
EnvironmentFile=/etc/sysconfig/slapd-current

ExecStart=/opt/openldap-current/libexec/slapd -u ldap -g ldap -h ${SLAPD_URLS} $SLAPD_OPTIONS

[Install]
WantedBy=multi-user.target

Create the environment file (/etc/sysconfig/slapd-current) specified in the previous step. It should have the following contents:

SLAPD_OPTIONS="-F /opt/openldap-current/etc/openldap/slapd.d"
SLAPD_URLS="ldapi:/// ldap:/// ldaps:///"

Configure the Server

Create a minimal server configuration and start it. First, create or obtain a TLS certificate. You don’t have to do this, but considering OpenLDAP is commonly used for authentication, it would ideal to encrypt communications with the server. If you decide to skip this, remove ldaps:/// from your environment file. I keep all of my TLS files in /pki. Create the /pki directory and a self-signed certificate with the following commands. Make sure the common name is the fully qualified domain name of your OpenLDAP server.

mkdir /pki
openssl req -days 500 -newkey rsa:4096 -keyout /pki/ldapkey.pem -nodes \
    -sha256 -x509 -out /pki/ldapcert.pem
chown $OWNER /pki/ldapkey.pem
chmod 400 /pki/ldapkey.pem
cat /pki/ldapcert.pem >> /pki/cacerts.pem

Edit the file /opt/openldap-current/etc/openldap/slapd.ldif and replace the entire thing with the following. If you opted to skip TLS, skip the lines that start with olcTLS.

dn: cn=config
objectClass: olcGlobal
cn: config
olcArgsFile: /opt/openldap-current/var/run/slapd.args
olcPidFile: /opt/openldap-current/var/run/slapd.pid
olcTLSCACertificateFile: /pki/cacerts.pem
olcTLSCertificateFile: /pki/ldapcert.pem
olcTLSCertificateKeyFile: /pki/ldapkey.pem
olcTLSCipherSuite: TLSv1.2:HIGH:!aNULL:!eNULL
olcTLSProtocolMin: 3.3

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

dn: cn=module,cn=config
objectClass: olcModuleList
cn: module
olcModulepath: /opt/openldap-current/libexec/openldap
olcModuleload: back_mdb.la
olcModuleload: pw-sha2.la

include: file:///opt/openldap-current/etc/openldap/schema/core.ldif
include: file:///opt/openldap-current/etc/openldap/schema/cosine.ldif
include: file:///opt/openldap-current/etc/openldap/schema/nis.ldif
include: file:///opt/openldap-current/etc/openldap/schema/inetorgperson.ldif
include: file:///opt/openldap-current/etc/openldap/schema/ppolicy.ldif

dn: olcDatabase=frontend,cn=config
objectClass: olcDatabaseConfig
objectClass: olcFrontendConfig
olcDatabase: frontend
olcPasswordHash: {SSHA512}
olcAccess: to * by dn.base="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth" manage by * none

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

Create the configuration directory, load the configuration ldif, and set the permissions on the configuration directory.

cd /opt/openldap-current/etc/openldap
mkdir slapd.d || rm -rf slapd.d/*
slapadd -n 0 -F slapd.d -l slapd.ldif
chown -R $OWNER slapd.d
chmod -R o-rwx slapd.d

Now load the unit file and start the server:

systemctl daemon-reload
systemctl start slapd-current

If everything went as it should, slapd should be up and running. Verify it is running with the command:

systemctl status slapd-current