Nagios XI - How To Use CA Certificates With check_ldaps Plugin

Overview

This KB article shows you how to use certificate authority (CA) certificates with the check_ldaps plugin.

Problem

When you try and execute the check_ldaps plugin:

/usr/local/nagios/libexec/check_ldaps -H dc01.domain.local -b '' -p 636

The following error is produced:

Could not bind to the LDAP server

If you enable the vebose mode -v for the plugin:

/usr/local/nagios/libexec/check_ldaps -H dc01.domain.local -b '' -p 636 -v

The following error is produced:

ldap_bind: Can't contact LDAP server (-1)
    additional info: TLS error -8179:Peer's Certificate issuer is not recognized.
Could not bind to the LDAP server

This verbose output has indicated that the plugin did not have a CA certificate to validate the certificate.

Resolution

You need to create the CA certificate on the Nagios server and configure openldap to use the certificate (check_ldaps plugin uses openldap).

You will need to obtain the CA certificate from your CA and open it in a text editor, you'll be copying the contents of the certificate into a file on the Nagios XI server.

Open an SSH session to your Nagios XI server.

Create Certificate

This example will create a certificate file called /etc/openldap/certs/windows_ca.cer and as you can imagine this is from a Microsoft Windows server.

Execute this command:

vi /etc/openldap/certs/windows_ca.cer

This opens the vi text editor.

Press i on the keyboard to go into insert mode.

Paste the contents of your CA certificate into the SSH session.

Press Escape on the keyboard to exit insert mode.

Type :wq and then press Enter (this will save the file and exit vi).

Update ldap.conf

Now you need to tell openldap to use this certificate. 

Execute this command:

vi /etc/openldap/ldap.conf

This opens the vi text editor.

Press i on the keyboard to go into insert mode.

Down arrow until you reach the end of the file

On a new line type the following:

TLS_CACERT /etc/openldap/certs/windows_ca.cer

Press Escape on the keyboard to exit insert mode.

Type :wq and then press Enter (this will save the file and exit vi).

Test Plugin

The check_ldaps plugin should now work:

/usr/local/nagios/libexec/check_ldaps -H dc01.domain.local -b '' -p 636

The following message is produced:

LDAP OK - 0.043 seconds response time|time=0.042861s;;;0.000000

Final Thoughts

For any support related questions please visit the Nagios Support Forums at:

http://support.nagios.com/forum/