Install and Setup OpenLDAP on Rocky Linux 8

In this guide, we provide a step by step tutorial on how to install and setup OpenLDAP on Rocky Linux 8. If you are here, then you already know what an OpenLDAP server is and thus the description of what it is is beyond the scope of this tutorial.

Installing OpenLDAP on Rocky Linux 8

Well, Rocky Linux 8 repositories do not provide OpenLDAP server packages.

To install the latest version of OpenLDAP server with bug fixes on Rocky Linux 8, you need to build it from the source as described in this guide.

Run System Update

To update your system packages, run the command;

dnf update

You can reboot after update;

reboot

Install Required Dependencies and Build Tools

There are quite a number of dependencies and build tools required for a successful build and compilation OpenLDAP from the source. Run the command below to install them.

dnf install epel-release -y

dnf install cyrus-sasl-devel make libtool autoconf \
openssl-devel libdb-devel tar gcc perl perl-devel wget vim -y

Install Libtool development libraries;

dnf --enablerepo=highavailability install -y

Install wiredtiger, provided by EPEL-7 repos;

cat > /etc/yum.repos.d/epel-release-7.repo << 'EOF'
[epel-release-7]
name=Extra Packages for Enterprise Linux 7 - x86_64
baseurl=https://dl.fedoraproject.org/pub/epel/7/x86_64/
enabled=0
gpgcheck=0
EOF

dnf --enablerepo=epel-release-7 install wiredtiger wiredtiger-devel

Create OpenLDAP System Account

In this demo, OpenLDAP will run with a non-privileged system user. Hence, run the command below to create OpenLDAP system user with custom user and group id;

useradd -r -M -d /var/lib/openldap -u 55 -s /usr/sbin/nologin ldap

Consult man useradd for the description of the command line options used above.

Download OpenLDAP Source Tarball

The latest stable release of OpenLDAP as of this writing is OpenLDAP 2.6.5.

Hence navigate to the OpenLDAP download’s page and grab the tarball.

VER=2.6.5

wget ftp://ftp.openldap.org/pub/OpenLDAP/openldap-release/openldap-$VER.tgz

Extract the OpenLDAP Source Tarball

The tarball can be extracted by running the command;

tar xzf openldap-$VER.tgz

Compile OpenLDAP on Rocky Linux 8

To compile OpenLDAP on Rocky Linux 8, you first need to run the configure script to adapt OpenLDAP to your system and check if any required dependency is missing before you can proceed with installation.

cd openldap-$VER

With configure script, you can enable or disable various options while building OpenLDAP.

./configure --prefix=/usr \
	--sysconfdir=/etc \
	--disable-static \
	--enable-debug \
	--with-tls=openssl \
	--with-cyrus-sasl \
	--enable-dynamic \
	--enable-crypt \
	--enable-spasswd \
	--enable-slapd \
	--enable-modules \
	--enable-rlookups \
	--enable-backends=mod \
	--disable-sql \
	--disable-wt \
	--enable-ppolicy \
	--enable-syslog \
	--enable-overlays=mod

To learn more about the configuration options, consult;

./configure --help

If the configure script completes with no issues, the last line you should see is;

...
Making servers/slapd/backends.c
    Add config ...
    Add ldif ...
    Add monitor ...
Making servers/slapd/overlays/statover.c
    Add ppolicy ...
Please run "make depend" to build dependencies

As the line states, you need to run the make depend command to build OpenLDAP dependencies.

make depend

Next, compile OpenLDAP on Rocky Linux 8.

make

If you got time and patience, you can run the test suite to verify OpenLDAP build for any errors. You can however skip this step.

make test

Install OpenLDAP on Rocky Linux 8

If the compilation of OpenLDAP completes successfully, proceed to install it by running the command;

make install

OpenLDAP configuration files are now installed on /etc/openldap.

ls -1 /etc/openldap/

certs
ldap.conf
ldap.conf.default
schema
slapd.conf
slapd.conf.default
slapd.ldif
slapd.ldif.default

The libraries are installed under /usr/libexec/openldap.

Configuring OpenLDAP on Rocky Linux 8

Now that the installation of OpenLDAP is complete, proceed to configure it.

Create OpenLDAP data and database directories

mkdir /var/lib/openldap /etc/openldap/slapd.d

Set the proper ownership and permissions on OpenLDAP directories and configuration files.

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

chown root:ldap /etc/openldap/slapd.conf

chmod 640 /etc/openldap/slapd.conf

Create OpenLDAP Systemd Service

In order to run OpenLDAP as a service, you need to create a systemd service file as shown below.

cat > /etc/systemd/system/slapd.service << 'EOL'
[Unit]
Description=OpenLDAP Server Daemon
After=syslog.target network-online.target
Documentation=man:slapd
Documentation=man:slapd-mdb

[Service]
Type=forking
PIDFile=/var/lib/openldap/slapd.pid
Environment="SLAPD_URLS=ldap:/// ldapi:/// ldaps:///"
Environment="SLAPD_OPTIONS=-F /etc/openldap/slapd.d"
ExecStart=/usr/libexec/slapd -u ldap -g ldap -h ${SLAPD_URLS} $SLAPD_OPTIONS

[Install]
WantedBy=multi-user.target
EOL

Save and quit the service file. Do not run/start the service yet.

Create OpenLDAP SUDO Schema

To configure LDAP with support sudo, first, check if your version of installed sudo supports LDAP.

sudo -V |  grep -i "ldap"

If sudo supports LDAP, you should see the lines below;

...
ldap.conf path: /etc/sudo-ldap.conf
ldap.secret path: /etc/ldap.secret

Check if LDAP sudo schema is available.

rpm -ql sudo |  grep -i schema.openldap

Output;

/usr/share/doc/sudo/schema.OpenLDAP

Copy the schema.OpenLDAP to the schema directory.

cp /usr/share/doc/sudo/schema.OpenLDAP  /etc/openldap/schema/sudo.schema

Next, you need to create sudo schema ldif file.

Run the command below to create the sudo.ldif file. (We copied the default ldif file from /usr/share/doc/sudo/schema.olcSudo and just modified it).

cat << 'EOL' > /etc/openldap/schema/sudo.ldif
dn: cn=sudo,cn=schema,cn=config
objectClass: olcSchemaConfig
cn: sudo
olcattributetypes: ( 1.3.6.1.4.1.15953.9.1.1
    NAME 'sudoUser'
    DESC 'User(s) who may  run sudo'
    EQUALITY caseExactMatch
    SUBSTR caseExactSubstringsMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )
#
olcattributetypes: ( 1.3.6.1.4.1.15953.9.1.2
    NAME 'sudoHost'
    DESC 'Host(s) who may run sudo'
    EQUALITY caseExactIA5Match
    SUBSTR caseExactIA5SubstringsMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
#
olcattributetypes: ( 1.3.6.1.4.1.15953.9.1.3
    NAME 'sudoCommand'
    DESC 'Command(s) to be executed by sudo'
    EQUALITY caseExactIA5Match
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
#
olcattributetypes: ( 1.3.6.1.4.1.15953.9.1.4
    NAME 'sudoRunAs'
    DESC 'User(s) impersonated by sudo (deprecated)'
    EQUALITY caseExactIA5Match
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
#
olcattributetypes: ( 1.3.6.1.4.1.15953.9.1.5
    NAME 'sudoOption'
    DESC 'Options(s) followed by sudo'
    EQUALITY caseExactIA5Match
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )
#
olcattributetypes: ( 1.3.6.1.4.1.15953.9.1.6
    NAME 'sudoRunAsUser'
    DESC 'User(s) impersonated by sudo'
    EQUALITY caseExactMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )
#
olcattributetypes: ( 1.3.6.1.4.1.15953.9.1.7
    NAME 'sudoRunAsGroup'
    DESC 'Group(s) impersonated by sudo'
    EQUALITY caseExactMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )
#
olcattributetypes: ( 1.3.6.1.4.1.15953.9.1.8
    NAME 'sudoNotBefore'
    DESC 'Start of time interval for which the entry is valid'
    EQUALITY generalizedTimeMatch
    ORDERING generalizedTimeOrderingMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 )
#
olcattributetypes: ( 1.3.6.1.4.1.15953.9.1.9
    NAME 'sudoNotAfter'
    DESC 'End of time interval for which the entry is valid'
    EQUALITY generalizedTimeMatch
    ORDERING generalizedTimeOrderingMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 )
#
olcattributeTypes: ( 1.3.6.1.4.1.15953.9.1.10
    NAME 'sudoOrder'
    DESC 'an integer to order the sudoRole entries'
    EQUALITY integerMatch
    ORDERING integerOrderingMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 )
#
olcobjectclasses: ( 1.3.6.1.4.1.15953.9.2.1 NAME 'sudoRole' SUP top STRUCTURAL
    DESC 'Sudoer Entries'
    MUST ( cn )
    MAY ( sudoUser $ sudoHost $ sudoCommand $ sudoRunAs $ sudoRunAsUser $ sudoRunAsGroup $ sudoOption $ sudoOrder $ sudoNotBefore $ sudoNotAfter $
        description )
    )
EOL

Update OpenLDAP SLAPD Database

Edit the SLAPD LDIF file, /etc/openldap/slapd.ldif, and update it as follows;

mv /etc/openldap/slapd.ldif /etc/openldap/slapd.ldif.bak

cat > /etc/openldap/slapd.ldif << 'EOL'
dn: cn=config
objectClass: olcGlobal
cn: config
olcArgsFile: /var/lib/openldap/slapd.args
olcPidFile: /var/lib/openldap/slapd.pid

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

dn: cn=module,cn=config
objectClass: olcModuleList
cn: module
olcModulepath: /usr/libexec/openldap
olcModuleload: back_mdb.la

include: file:///etc/openldap/schema/core.ldif
include: file:///etc/openldap/schema/cosine.ldif
include: file:///etc/openldap/schema/nis.ldif
include: file:///etc/openldap/schema/inetorgperson.ldif
include: file:///etc/openldap/schema/sudo.ldif
#include: file:///etc/openldap/schema/ppolicy.ldif
dn: olcDatabase=frontend,cn=config
objectClass: olcDatabaseConfig
objectClass: olcFrontendConfig
olcDatabase: frontend
olcAccess: to dn.base="cn=Subschema" by * read
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
EOL

• To update the SLAPD database from the information provided on the SLAPD LDIF file above, use slapadd command with the option -n 0 which creates the first database.
• To specify the configuration directory, /etc/openldap/slapd.d, use option -F and option -l to specify location of the LDIF file above.

Before you can write the changes to the database, perform a dry run to see what would happen. Pass -u option to slapadd command.

slapadd -n 0 -F /etc/openldap/slapd.d -l /etc/openldap/slapd.ldif -u

Then implement the changes if there is no error;

slapadd -n 0 -F /etc/openldap/slapd.d -l /etc/openldap/slapd.ldif

This command creates slapd database configurations under /etc/openldap/slapd.d directory.

ls /etc/openldap/slapd.d

'cn=config'  'cn=config.ldif'

Set the user and group ownership of the /etc/openldap/slapd.d directory and the files in it to ldap user.

chown -R ldap:ldap /etc/openldap/slapd.d

Running SLAPD Service

Reload systemd configurations and start and enable OpenLDAP service to run on boot.

systemctl daemon-reload

systemctl enable --now slapd

Check the status;

systemctl status slapd

● slapd.service - OpenLDAP Server Daemon
   Loaded: loaded (/etc/systemd/system/slapd.service; enabled; vendor preset: disabled)
   Active: active (running) since Wed 2023-08-02 00:06:58 EDT; 9s ago
     Docs: man:slapd
           man:slapd-mdb
  Process: 101987 ExecStart=/usr/libexec/slapd -u ldap -g ldap -h ${SLAPD_URLS} $SLAPD_OPTIONS (code=exited, status=0/SUCCESS)
 Main PID: 101988 (slapd)
    Tasks: 2 (limit: 11131)
   Memory: 3.1M
   CGroup: /system.slice/slapd.service
           └─101988 /usr/libexec/slapd -u ldap -g ldap -h ldap:/// ldapi:/// ldaps:/// -F /etc/openldap/slapd.d

Aug 02 00:06:58 localhost.localdomain systemd[1]: Starting OpenLDAP Server Daemon...
Aug 02 00:06:58 localhost.localdomain slapd[101987]: @(#) $OpenLDAP: slapd 2.6.5 (Aug  1 2023 15:41:52) $
                                                             [email protected]:/root/openldap-2.6.5/servers/slapd
Aug 02 00:06:58 localhost.localdomain slapd[101988]: slapd starting
Aug 02 00:06:58 localhost.localdomain systemd[1]: Started OpenLDAP Server Daemon.

Configure OpenLDAP Logging on Rocky Linux 8

To enable OpenLDAP to log connections, operations, results statistics, create and ldif file and update the database as follows. Such OpenLDAP logging is enabled on log level 256 with keyword stats by modifying the olcLogLevel attribute as shown below.

cd ~

cat > enable-openldap-log.ldif << 'EOL'
dn: cn=config
changeType: modify
replace: olcLogLevel
olcLogLevel: stats
EOL

ldapmodify -Y external -H ldapi:/// -f enable-openldap-log.ldif

ldapsearch -Y EXTERNAL -H ldapi:/// \
-b cn=config "(objectClass=olcGlobal)" olcLogLevel -LLL -Q

dn: cn=config
olcLogLevel: stats

Configure Rsyslog to enable OpenLDAP to log to a specific file. By default, OpenLDAP logs to local4 facility.

echo "local4.* /var/log/slapd.log" >> /etc/rsyslog.conf

Restart Rsyslog

systemctl restart rsyslog

You should now be able to read the LDAP logs on, /var/log/slapd.log.

Update log rotation;

sed -i '/{/i /var/log/slapd.log'  /etc/logrotate.d/syslog

You syslog log rotation config should now look like;

cat /etc/logrotate.d/syslog

/var/log/cron
/var/log/maillog
/var/log/messages
/var/log/secure
/var/log/spooler
/var/log/slapd.log
{
    missingok
    sharedscripts
    postrotate
        /usr/bin/systemctl -s HUP kill rsyslog.service >/dev/null 2>&1 || true
    endscript
}

Create OpenLDAP Default Root DN

Next, create MDB database defining the root DN as well as the access control lists.

First, generate the root DN password.

slappasswd

New password: ENTER PASSWORD
Re-enter new password: RE-ENTER PASSWORD
{SSHA}QSFUa8itfMYx3t3DNyAkvL0X+w2e6SXr

Paste the password hash generated above as the value of olcRootPW in the Root DN ldif file below.

Replace the domain components, dc=ldapmaster,dc=kifarunix-demo,dc=com with your appropriate names.

cat > rootdn.ldif << 'EOL'
dn: olcDatabase=mdb,cn=config
objectClass: olcDatabaseConfig
objectClass: olcMdbConfig
olcDatabase: mdb
olcDbMaxSize: 42949672960
olcDbDirectory: /var/lib/openldap
olcSuffix: dc=ldapmaster,dc=kifarunix-demo,dc=com
olcRootDN: cn=admin,dc=ldapmaster,dc=kifarunix-demo,dc=com
olcRootPW: {SSHA}QSFUa8itfMYx3t3DNyAkvL0X+w2e6SXr
olcDbIndex: uid pres,eq
olcDbIndex: cn,sn pres,eq,approx,sub
olcDbIndex: mail pres,eq,sub
olcDbIndex: objectClass pres,eq
olcDbIndex: loginShell pres,eq
olcDbIndex: sudoUser,sudoHost pres,eq
olcAccess: to attrs=userPassword,shadowLastChange,shadowExpire
  by self write
  by anonymous auth
  by dn.subtree="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth" manage 
  by dn.subtree="ou=system,dc=ldapmaster,dc=kifarunix-demo,dc=com" read
  by * none
olcAccess: to dn.subtree="ou=system,dc=ldapmaster,dc=kifarunix-demo,dc=com" by dn.subtree="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth" manage
  by * none
olcAccess: to dn.subtree="dc=ldapmaster,dc=kifarunix-demo,dc=com" by dn.subtree="gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth" manage
  by users read 
  by * none
EOL

Read more about ACL on OpenLDAP Access Control.

Updated the slapd database with the content above;

ldapadd -Y EXTERNAL -H ldapi:/// -f rootdn.ldif

Sample command output;

SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
adding new entry "olcDatabase=mdb,cn=config"

Configure OpenLDAP with SSL/TLS

To secure OpenLDAP communication between the client and the server, configured it to use SSL/TLS certificates.

In this guide, we are self-signed certificates. You can choose to obtain the commercially signed and trusted certificates from your preferred CAs, for production environments.

openssl req -x509 \
	-nodes \
	-days 3650 \
	-newkey rsa:2048 \
	-keyout /etc/pki/tls/ldapserver.key \
	-out /etc/pki/tls/ldapserver.crt

chown ldap:ldap /etc/pki/tls/{ldapserver.crt,ldapserver.key}

Update the OpenLDAP Server TLS certificates attributes.

cat > add-tls.ldif << 'EOL'
dn: cn=config
changetype: modify
add: olcTLSCACertificateFile
olcTLSCACertificateFile: /etc/pki/tls/ldapserver.crt
-
add: olcTLSCertificateKeyFile
olcTLSCertificateKeyFile: /etc/pki/tls/ldapserver.key
-
add: olcTLSCertificateFile
olcTLSCertificateFile: /etc/pki/tls/ldapserver.crt
EOL

Note that we have used self-signed certificate as both the certificate and the CA certificate.

ldapadd -Y EXTERNAL -H ldapi:/// -f add-tls.ldif

You can confirm this by running;

slapcat -b "cn=config" | grep olcTLS

olcTLSCACertificateFile: /etc/pki/tls/ldapserver.crt
olcTLSCertificateKeyFile: /etc/pki/tls/ldapserver.key
olcTLSCertificateFile: /etc/pki/tls/ldapserver.crt

Change the location of the CA certificate on /etc/openldap/ldap.conf.

vim /etc/openldap/ldap.conf

...
#TLS_CACERT     /etc/pki/tls/cert.pem
TLS_CACERT     /etc/pki/tls/ldapserver.crt
...

Save and exit the file.

Create OpenLDAP Base DN

Next, create your base DN or search base to define your organization structure and directory.

Replace the domain components and organization units accordingly.

cat > basedn.ldif << 'EOL'
dn: dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: dcObject
objectClass: organization
objectClass: top
o: Kifarunix-demo
dc: ldapmaster

dn: ou=groups,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: organizationalUnit
objectClass: top
ou: groups

dn: ou=people,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: organizationalUnit
objectClass: top
ou: people
EOL

ldapadd -Y EXTERNAL -H ldapi:/// -f basedn.ldif

Create OpenLDAP User Accounts

You can add users to your OpenLDAP server. Create an ldif file to define your users as follows.

cat > users.ldif << 'EOL'
dn: uid=johndoe,ou=people,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
uid: johndoe
cn: John
sn: Doe
loginShell: /bin/bash
uidNumber: 10000
gidNumber: 10000
homeDirectory: /home/johndoe
shadowMax: 60
shadowMin: 1
shadowWarning: 7
shadowInactive: 7
shadowLastChange: 0

dn: cn=johndoe,ou=groups,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: posixGroup
cn: johndoe
gidNumber: 10000
memberUid: johndoe
EOL

Add the user to the OpenLDAP database.

ldapadd -Y EXTERNAL -H ldapi:/// -f users.ldif

Setting password for LDAP User

To set the password for user above, run the command below;

ldappasswd -H ldapi:/// -Y EXTERNAL \
-S "uid=johndoe,ou=people,dc=ldapmaster,dc=kifarunix-demo,dc=com"

Create OpenLDAP Bind DN and Bind DN User

Bind DN user is used for performing LDAP operations such as resolving User IDs and group IDs. In this guide, we create a bind DN ou called system. Note the access controls associated with this ou as defined on the root DN above.

List the Access control lists on the database;

ldapsearch -Q -LLL -Y EXTERNAL -H ldapi:/// \
-b cn=config '(olcDatabase={1}mdb)' olcAccess

Create the BindDN user password.

slappasswd

New password: Password
Re-enter new password: Password
{SSHA}lyFDLUYjo+JB4wRm+S9bzjAW0svJugjj

Paste the password hash value above as the value of userPassword attribute in the file below;

cat > bindDNuser.ldif << 'EOL'
dn: ou=system,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: organizationalUnit
objectClass: top
ou: system

dn: cn=readonly,ou=system,dc=ldapmaster,dc=kifarunix-demo,dc=com
objectClass: organizationalRole
objectClass: simpleSecurityObject
cn: readonly
userPassword: {SSHA}lyFDLUYjo+JB4wRm+S9bzjAW0svJugjj
description: Bind DN user for LDAP Operations
EOL

ldapadd -Y EXTERNAL -H ldapi:/// -f bindDNuser.ldif

Implement OpenLDAP Password Policies

To ensure that you can enforce password complexity policies from OpenLDAP server, check the guide below;

Implement OpenLDAP Password Policies

Allow OpenLDAP Service on Firewall

To allow remote clients to query OpenLDAP server, allow the ldap (389 UDP/TCP) and ldaps (636 UDP/TCP) service on firewall.

firewall-cmd --add-service={ldap,ldaps} --permanent

firewall-cmd --reload

Testing OpenLDAP Authentication

Well, there you go. You have learnt how to install and setup OpenLDAP server on Rocky Linux 8.

To verify that users can actually connect to the systems via the OpenLDAP server, you need to configure OpenLDAP clients on the remote systems.

e the guide below;

Configure SSSD for LDAP Authentication on Rocky Linux 8

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