Introduction and Concepts
This is a guide on how to configure an Archlinux installation to authenticate against an OpenLDAP server.The openldap backend can be either local (installed on the same computer) or network (i.e in a lab environment where central authentication is desired). The guide will be divided in two parts. The first part deals with how to setup OpenLDAP locally and the second with how to setup the NSS and PAM modules required for the authentication scheme to work. If you just want to configure Arch to authenticated against an already excisting LDAP server then you can skip to the second part.
OpenLDAP is an open-source server implementation of the LDAP protocol. It is mainly used as an authentication backend to various services (the most famous one being Samba, which is used to emulate a domain controller) and basically holds the user data. The closest analogue to real life, would be the telephone directory. Another generalised explanation of what an LDAP server does is that it is a database (which it basically is, but it is not relational) which is optimised for accessing the data and not reading them.
Commands relate to OpenLDAP that begin with ldap (like ldapsearch) are client-side utilities while commands that begin with slap (like slapcat) are server-side. Arch packages both in thepackage, so you need to install it regardless of o local or network OpenLDAP install.
NSS and PAM
NSS (which stands for Name Service Switch) is a system mechanism to configure different sources for common configuration databases. For example,
/etc/passwd is a
file type source for the passwd database.
PAM (which stands for Pluggable Authentication Module) is a machanism Linux (and most *nixes) uses to extend it's authentication schemes based on different plugins.
So to summarize, we need to configure NSS to use the OpenLDAP server as a source for the
shadow and other configuration databases and then configure PAM to use these sources to authenticate it's users.
You can read about installation and basic configuration in the OpenLDAP article. After you have completed that, return here.
Populate LDAP Tree with Base Data
Create a file called base.ldif with the following text:
# example.org dn: dc=example,dc=org objectClass: dcObject objectClass: organization o: Example Organization dc: example # Manager, example.org dn: cn=Manager,dc=example,dc=org cn: Manager description: LDAP administrator roleOccupant: dc=example,dc=org objectClass: organizationalRole objectClass: top # People, example.org dn: ou=People,dc=example,dc=org ou: People objectClass: top objectClass: organizationalUnit # Group, example.org dn: ou=Group,dc=example,dc=org ou: Group objectClass: top objectClass: organizationalUnit
Add it to your OpenLDAP Tree:
ldapadd -x -D "cn=Manager,dc=example,dc=org" -W -f base.ldif
Test to make sure the data was imported:
ldapsearch -x -b 'dc=example,dc=org' '(objectclass=*)'
Configure TLS Encryption
It's a good idea to configure TLS to encrypt the exchange of information between client and server. This way passwords, which are normally sent plain-text, cannot be easily sniffed from the wire. In order to use TLS, we must first create a certificate. You can have a certificate signed, or create your own Certificate Authority (CA), but for our purposed, a self-signed certificate will suffice. IMPORTANT: OpenLDAP cannot use a certificate that has a password associated to it.
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/ (if this directory doesn't exist create it) and secure them. IMPORTANT: 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:
cp slapdcert.pem slapdkey.pem /etc/openldap/ssl/ chown ldap slapdkey.pem chmod 400 slapdkey.pem chmod 444 slapdcert.pem
Edit the daemon configuration file (
/etc/openldap/slapd.conf) to tell LDAP where the certificate files reside by adding the following lines:
# Certificate/SSL Section TLSCipherSuite HIGH:MEDIUM:+SSLv2 TLSCertificateFile /etc/openldap/ssl/slapdcert.pem TLSCertificateKeyFile /etc/openldap/ssl/slapdkey.pem
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: HIGH, MEDIUM, and +SSLv2 are all wildcards.
To see which ciphers are supported by your local OpenSSL installation, type the following:
openssl ciphers -v ALL
In order to tell OpenLDAP to start using encryption, edit /etc/conf.d/slapd, uncomment the SLAPD_SERVICES line and set it to the following:
This will cause OpenLDAP to accept encrypted. IMPORTANT: If you created a self-signed certificate above be sure to add the following line to /etc/openldap/ldap.conf or you won't be able connect to the server to test it:
Restart the server:
Test that the server is encrypting traffic run the following command:
ldapsearch -x -H ldaps://example.org -b 'dc=example,dc=org' '(objectclass=*)'
Before you begin setting up PAM and NSS for ldap authentication, you should try to check if the LDAP server is available. You can do this easily with ldapsearch.
You can search an LDAP server with the following command:
ldapsearch -x -H <URL> -b <BASE>
You can add the URL and BASE settings to
/etc/openldap/ldap.conf in order to avoid writing the everytime. All client-side ldap utilities use this file to read some general variables.
host <SERVER_IP> base dc=example,dc=org rootbinddn cn=admin,dc=example,dc=org port 636 pam_login_attribute uid pam_template_login_attribute uid nss_base_passwd ou=People,dc=example,dc=org?one nss_base_shadow ou=People,dc=example,dc=org?one nss_base_group ou=Group,dc=example,dc=org?one ssl start_tls ssl on # This is only needed if you're using a self-signed certificate. tls_checkpeer no
passwd: files ldap group: files ldap shadow: files ldap
host <SERVER_IP> base dc=example,dc=org rootbinddn cn=admin,dc=example,dc=org port 636 pam_login_attribute uid pam_template_login_attribute uid nss_base_passwd ou=People,dc=example,dc=org?one nss_base_shadow ou=People,dc=example,dc=org?one nss_base_group ou=Group,dc=example,dc=org?one ssl start_tls ssl on # This is only needed if your using a self-signed certificate. tls_checkpeer no
auth requisite pam_securetty.so auth requisite pam_nologin.so auth sufficient pam_ldap.so auth required pam_env.so auth required pam_unix.so nullok try_first_pass account sufficient pam_ldap.so account required pam_access.so account required pam_unix.so session required pam_motd.so session required pam_limits.so session optional pam_mail.so dir=/var/spool/mail standard session optional pam_lastlog.so session required pam_unix.so
password sufficient pam_ldap.so password required pam_unix.so shadow md5 nullok
auth sufficient pam_ldap.so auth sufficient pam_rootok.so auth required pam_unix.so account sufficient pam_ldap.so account required pam_unix.so session sufficient pam_ldap.so session required pam_unix.so password sufficient pam_ldap.so password required pam_permit.so
auth sufficient pam_ldap.so auth sufficient pam_rootok.so auth required pam_unix.so use_first_pass account sufficient pam_ldap.so account required pam_unix.so session sufficient pam_ldap.so session required pam_unix.so
auth sufficient pam_ldap.so auth required pam_securetty.so #Disable remote root auth required pam_unix.so try_first_pass auth required pam_nologin.so auth required pam_env.so account sufficient pam_ldap.so account required pam_unix.so account required pam_time.so password sufficient pam_ldap.so password required pam_unix.so session required pam_unix_session.so session required pam_limits.so
auth sufficient pam_ldap.so auth required pam_unix.so account sufficient pam_ldap.so account required pam_unix.so password sufficient pam_ldap.so password required pam_unix.so session required pam_unix.so
Name Service Cache Daemon
READ THIS FIRST: [NSCD Bugged in Arch Linux]
mkdir -p /var/db/nscd/ mkdir -p /var/run/nscd/
Links and Resources
One of the best OpenLDAP clients: [phpLDAPadmin]
Debian OpenLDAP setup: [Using LDAP for single authentication]
How to integrate OpenLDAP for MacOSX, Windows and Linux: [Heterogeneous Network Authentication Introduction]