LDAP (Lightweight Directory Access Protocol)

LDAP is used by The Company on its production servers to authenticate users. Configuration is split into two parts, the LDAP server config and the LDAP client setup.
The previous version of LDAP used dc=oldcompany,dc=com as it's base DN, but the new base DN is dc=int, dc=TheCompany dc=com.

Confusingly, there are two files called ldap.conf on the server (and maybe on other servers too), /etc/ldap.conf is the CLIENT config file, /etc/openldap/ldap.conf is part of the SERVER config in conjunction with /etc/openldap/slapd.conf.

To add users and groups, see Add Users and Groups to LDAP.

Testing Methodology, see page:- Testing LDAP

LDAP attributes match /etc/passwd fields according to the illustration below:-
LDAP to passwd correlation

LDAP Server Config

LDAP is not used for authentication on inet03/04 to prevent lockouts. Hence local accounts are needed for users. Use useradd to create them.

useradd -d /home/user123 -g noc -s /bin/bash -c "MyUser 123" -m user123

TLS encryption is used in preference to SSL because TLS encryption uses the standard unencrypted LDAP port, SSL needs another port opening which would require firewall rules creating.

TLS encryption is started automatically if the client is configured to use it, ldap log files look like:-

Jun 16 13:01:40 inet03 slapd[28776]: conn=84 op=0 STARTTLS
Jun 16 13:01:40 inet03 slapd[28776]: conn=84 op=0 RESULT oid= err=0 text=
Jun 16 13:01:40 inet03 slapd[28776]: conn=84 fd=23 TLS established tls_ssf=128 ssf=128

Background Reading

Local info

The master LDAP server is inet03, all updates should be carried on on this server.


[root@inet03 openldap]# pwd
[root@inet03 openldap]# ls -l
total 28
drwxr-xr-x  2 root root 4096 Jul  2  2008 cacerts       <----- Certificate Directory
-rw-r--r--  1 root root  330 Nov 26  2008 ldap.conf     <----- Client Config file
drwxr-xr-x  3 root root 4096 Jan  5  2009 schema        <----- Schema files describing object classes
-rw-r-----  1 root ldap 3930 Nov 24 09:50 slapd.conf    <----- Server Config file

Logging is set to use syslog and syslog.conf directs openLDAP logs to /etc/openldap/openldap.log. By default, this log file is not rotated with logrotate. Ther verbosity of the logging is controlled by a number in the config file which is made up of logging levels added together, see OpenLDAP logging levels.

In slapd.conf, add some logging directives,

logfile                 /var/log/openldap/openldap.log
loglevel                256
#loglevel               -1

Logging seems to be via syslog even with a logfile line, so we need to specify where logging actually goes, in /etc/syslog.conf add these to the bottom and restart syslog. The path to the filename must exist so mkdir it if it doesn't:-

local4.*                                                -/var/log/openldap/openldap.log

Secure SSL LDAP access

Secure operation with TLS or ssl relies on a correct server certificate being available and some lines in slapd.conf.

TLSCACertificateFile    /etc/openldap/certs/inticacert.pem
TLSCertificateFile      /etc/openldap/certs/inet03.ldap-cert.pem
TLSCertificateKeyFile   /etc/openldap/certs/inet03.ldap.key

TLSVerifyUser never
TLSVerifyClient allow

SSL certs live in /etc/openldap/certs/ and are issued to inet03/4.prod.int.TheCompany.com. The directory should look like this:-

[root@inet03 certs]# tree -L 2 /etc/openldap/certs/
|-- inet03.ldap-cert.pem
|-- inet03.ldap-csr.pem
|-- inet03.ldap.key
|-- Thecompany-cacert.pem
|-- ldap-client-cert.pem

Creating ssl CSR and Key.

[root@inet04 certs]# openssl genrsa -out inet04.gyprod.int.TheCompany.com.key 2048
Generating RSA private key, 2048 bit long modulus
e is 65537 (0x10001)

[root@inet04 certs]# openssl req -new -key inet04.gyprod.int.TheCompany.com.key -out inet04.gyprod.int.TheCompany.com-csr.pem
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
Country Name (2 letter code) [GB]:GG
State or Province Name (full name) [Berkshire]:Guernsey
Locality Name (eg, city) [Newbury]:Guernsey
Organization Name (eg, company) [My Company Ltd]:The Company
Organizational Unit Name (eg, section) []:
Common Name (eg, your name or your server's hostname) []:inet04.gyprod.int.TheCompany.com
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

Secure vs non-secure operation

The operation of the secure and non-secure servers is controlled by a file in /etc/sysconfig:-

[root@inet03 sysconfig]# cat /etc/sysconfig/ldap
# Parameters to ulimit called right before starting slapd
# - use this to change system limits for slapd

# How long to wait between sending slapd TERM and KILL
# signals when stopping slapd by init script
# - format is the same as used when calling sleep

# By default only listening on ldap:/// is turned on.
# If you want to change listening options for slapd,
# set following three variables to yes or no

The SLAPD_LDAPS was set to yes to enable SSL access, but this is not required for TLS as TLS uses an insecure channel and negotiates a secure connection over it. This is the same way that TLS works with SMTP email.

Start the daemon with service ldap start, check for listening connections with:-

[root@inet03 certs]# netstat -lt | grep ldap
tcp        0      0 *:ldap                      *:*                         LISTEN
tcp        0      0 *:ldaps                     *:*                         LISTEN
tcp        0      0 *:ldap                      *:*                         LISTEN
tcp        0      0 *:ldaps                     *:*                         LISTEN

Test Config file syntax:-

[root@inet03 certs]# slaptest
config file testing succeeded



inet03 has a replica on inet04. Replicas will need to be help on inet01 and inet02 in xxx.

In LDAP-speak, inet03 is a provider, whilst inet04 is a consumer. All replication is done using syncrepl, slurpd is not used at all.

inet04 acts as a consumer and replicates its LDAP data base from the provider server, net03, the config for this is in /etc/openldap/slapd.conf at the bottom:-

syncrepl rid=123

Testing Access

ldapsearch -x -W -D  'cn=Manager,dc=int, dc=TheCompany, dc=com' -b "" -s base -h inet03

-x Simple Auth, not SASL
-W Prompt for simple Auth, not on command line
-D Distinguished name to bind with
-b search Base
-s Scope of search, base, onelevel or subtree.
-h Host to search on
-S attr, sort the results by attribute 'attr' (see below)

eg. to see all users and UID's:-
ldapsearch -x -W -D 'uid=astringer,ou=People,dc=TheCompany, dc=com' -b 'ou=People,dc=TheCompany, dc=com' -s onelevel | grep -E 'cn:|uidN|# '

eg. to see just one user:-
ldapsearch -x -W -D 'uid=astringer,ou=People,dc=int, dc=TheCompany, dc=com' -b 'cn=testuser,ou=People,dc=int, dc=TheCompany, dc=com' -s base

eg. to get email address for one user:-
 ldapsearch -x -W -D 'uid=astringer,ou=People,dc=int, dc=TheCompany, dc=com' -b 'cn=testuser,ou=People,dc=int, dc=TheCompany, dc=com' -s base mail
Enter LDAP Password:
# extended LDIF
# LDAPv3
# base <cn=testuser,ou=People,dc=prod,dc=wagerware,dc=net> with scope base
# filter: (objectclass=*)
# requesting: mail

# testuser, People, prod.wagerware.net
dn: cn=testuser,ou=People,dc=int, dc=TheCompany, dc=com
mail: test.user@TheCompany.com

# search result
search: 2
result: 0 Success

# numResponses: 2
# numEntries: 1

use -L or -LLL to reduce the “clutter” returned and just leave the query result.

Sorting attributes, can produce oddities, sort by gidNumber below returns the gid value sorted by first digit, not whole value:-

ldapsearch -x -W -D 'uid=astringer,ou=People,dc=prod, dc=product, dc=net' -b 'ou=Group,dc=prod, dc=product, dc=net' -S gidNumber -s sub cn gidNumber  
cn: codebldr
gidNumber: 2046

cn: technicalops
gidNumber: 205

cn: TechnicalOpsGIB
gidNumber: 205

To get attributes eg. uid where you know a different attribute, eg. cn:-

[root@inet01 ~]# ldapsearch -h inet01 -x -W -D 'cn=Manager,dc=product,dc=net' "(cn=Usrname Desiraj)" uid userPassword uidNumber
Enter LDAP Password:
# extended LDIF
# LDAPv3
# base <> with scope sub
# filter: (cn=Username Desiraj)
# requesting: uid userPassword uidNumber

# Username Desiraj, People, prod.product.net
dn: cn=username Desiraj,ou=People,dc=prod,dc=product,dc=net
userPassword:: e01ENX1UV2U4ZTBBM2tjYzRHR29kam9MSXFBPT0=
uidNumber: 8857
uid: username23

# search result
search: 2
result: 0 Success

# numResponses: 2
# numEntries: 1

Web Access

Client Side setup

Several files need editing to enable ldap access, lines or blocks of directives which require changing are shown below, lines which are left alone are not shown for clarity:-

[root@inet03 pam.d]# more /etc/ldap.conf
# This is the configuration file for the LDAP nameservice
# switch library and the LDAP PAM module.
host inet02 inet01

# The distinguished name of the search base.
#base dc=example,dc=com
base dc=prod,dc=product,dc=net
[root@inet03 pam.d]# more /etc/nsswitch.conf
# /etc/nsswitch.conf

passwd:     files ldap
shadow:     files ldap
group:      files ldap

#hosts:     db files nisplus nis dns
hosts:      files dns

ethers:     files
netmasks:   files
networks:   files
protocols:  files ldap
rpc:        files
services:   files ldap

netgroup:   files ldap

publickey:  nisplus

automount:  files ldap
aliases:    files
[root@inet03 pam.d]# cat /etc/openldap/ldap.conf
#BASE   dc=example, dc=com
#URI    ldap://ldap.example.com ldap://ldap-master.example.com:666

#SIZELIMIT      12
#TIMELIMIT      15
#DEREF          never
#URI ldap://
URI ldap://inet02 ldap://inet01

#BASE dc=example,dc=com
BASE dc=prod,dc=product,dc=net

TLS_CACERTDIR /etc/openldap/cacerts
[root@inet03 pam.d]#

For TLS operation, the root CAcerts file must be copied to TLS_CACERTDIR, as above.

Add the pam module to /etc/pam.d/sshd to auto create home directories:-

[root@inet03 pam.d]# cat sshd
auth       include      system-auth
account    required     pam_nologin.so
account    include      system-auth
password   include      system-auth
session    optional     pam_keyinit.so force revoke
session    include      system-auth
session    required     pam_mkhomedir.so skel=/etc/skel/ umask=0077
session    required     pam_loginuid.so

Also you can add this line to a pam file like /etc/pam.d/sshd:-

account    required     pam_access.so accessfile=/etc/security/access-login.conf

Users must additionally be listed in /etc/security/access-login.conf to allow logins.

Test LDAP access with ldapsearch -x.


In /root/scripts there is a bash script which dumps the LDAP database to LDIF. A separate script on noc01 copies this data base to BigCity for off-site storage.

rb/ldaphowto.txt · Last modified: 20/08/2019 14:47 by andrew