This is a multi-part article where I will cover different areas of configuration of OpenLDAP server in CentOS 7 Linux node. You can use below links to refer different parts of this tutorial
- Basics LDAP Tutorial for Beginners – Understanding Terminologies & Usage
- Step-by-Step Tutorial: Install and Configure OpenLDAP
- Step-by-Step Tutorial: Configure OpenLDAP with TLS certificates
- Step-by-Step Tutorial: Configure LDAP client to authenticate with LDAP server
First let us install all the required openldap client and dependent packages
Since we plan to use authconfig to configure ldap client for our RHEL/CentOS 7 Linux node, we only install SSSD and authconfig packages. oddjob-mkhomedir is required to be able to create active directory user's home directory automatically.
[root@ldap-client ~]# yum install authconfig authconfig-gtk openldap-clients sssd oddjob-mkhomedir.x86_64 -y
nss-pam-ldapd, pam_ldap. We will only use SSSD hence will not cover this part in our tutorial
Configure LDAP client to authenticate with LDAP server
Before you start make sure you copy /etc/openldap/cacerts/ca.cert.pem from the ldap-server to ldap-client in the same location under /etc/openldap/cacerts/ca.cert.pem. This key will be referred by the authconfig tool
Method 1: Using authconfig-tui
Configuring a client system to use an LDAP directory for user authentication is as easy as pie on a Fedora or RHEL system. Fedora has command-line utilities as well as GUI tools (for example, system-config-authentication, authconfig-gtk) that make it easy.
One of the command-line tools is provided by the package authconfig. To launch the tool from the command line, type the following:
[root@ldap-client ~]# authconfig-tui
A screen similar to the one shown next will appear:
- In the Authentication Configuration screen, navigate to (using TAB on your keyboard) and then select (using SPACEBAR on your keyboard) the following:
Use LDAP → Under theUser Informationsection
Use LDAP Authentication → Under theAuthenticationsection - Navigate to the Next button and press ENTER to select it.
- Use the following information to complete the fields in the ensuing LDAP Settings screen:
Server:ldap://10.0.2.20/
Base DN:dc=example,dc=com
- When we click OK, this will automatically change a series of files that otherwise would have to be changed by hand. For example, it will add the following lines to the
/etc/openldap/ldap.conffile:
URI ldap://10.0.2.20/
BASE dc=example,dc=com
TLS_CACERTDIR /etc/openldap/cacerts
TLS_CACERTDIR and add TLS_REQCERT never
Method 2: Using authconfig CLI
You can also configure ldap on the client using authconfig as shown below
[root@ldap-client ~]# authconfig --enableldap --enableldapauth --ldapserver=10.0.2.20 --ldapbasedn="dc=example,dc=com" --enableldaptls --update
authconfig-tui, you can skip the configuration using authconfig.
Configure OpenLDAP
Next configure your openldap client to communicate with the ldap server and the communication method. Add the below content in /etc/openldap/ldap.conf
BASE dc=example,dc=com URI ldap://10.0.2.20 TLS_CACERTDIR /etc/openldap/cacerts
Could not start TLS encryption. TLS: hostname does not match CN in peer certificate" error in /var/log/messages after restarting sssd then it means your client's hostname is not configured to use the CA certificate. In such case you must have a proper certificate generated for this client of use SAN certificate on the ldap server. Alternatively you can disable TLS check using TLS_REQCERT never in /etc/openldap/ldap.conf and also ldap_id_use_start_tls = False in /etc/sssd/sssd.conf. But this will disable the TLS communication hence making the system insecure.
Configure oddjob-mkhomedir to auto create home directories
We can use oddjob-mkhomedir to create home directories automatically for any ldap user which logs into the client node. This requires pam_mkhomedir.so provided by ddjob-mkhomedir which we had already installed earlier.
Modify the PAM configuration to use pam_oddjob_mkhomedir. For example, add this line at the bottom of /etc/pam.d/system-auth:
session required pam_oddjob_mkhomedir.so
Next enable and start oddjobd.service
[root@ldap-client ~]# systemctl enable oddjobd.service --now
/etc/pam.d/sshd) uses /etc/pam.d/password-auth file instead of /etc/pam.d/system-auth. Hence, it also required to append the above line in /etc/pam.d/password-auth file, in order to create home directories while logging via ssh.Instead of manual editing, the authconfig command can be used:
[root@ldap-client ~]# authconfig --enablemkhomedir --updateall
Also restart sssd.service
[root@ldap-client ~]# systemctl restart sssd.service
Create LDAP user (Optional)
You can ignore this step if you already a ldap user.
In order to authenticate as an LDAP user, when we create the user, we have to include a series of fields, such as shell, uid, gid, etc. As an example, let’s add the user testuser1. We begin by creating the testuser1.ldif file, with the following content:
[root@ldap-client ~]# cat testuser1.ldif
dn: uid=testuser1,ou=users,dc=example,dc=com
uid: testuser1
cn: testuser1
objectClass: shadowAccount
objectClass: top
objectClass: person
objectClass: inetOrgPerson
objectClass: posixAccount
userPassword: {SSHA}5rMM/3f8Ki13IyarGTtwzieoTu7KMgwc
shadowLastChange: 17016
shadowMin: 0
shadowMax: 99999
shadowWarning: 7
loginShell: /bin/bash
uidNumber: 1001
gidNumber: 1001
homeDirectory: /home/testuser1
sn: testuser1
mail: testuser1@example.com
testuser1 using slappasswd on ldap-server node. My password for testuser1 is test
Create LDAP group (Optional)
You can ignore this step if you already a ldap group.
Also we will need a group for this testuser1 so I will add it to our existing OU "users"
[root@ldap-client ~]# cat groups.ldif
dn: cn=testuser1,ou=users,dc=example,dc=com
objectClass: posixGroup
objectClass: top
cn: testuser1
userPassword: {crypt}x
gidNumber: 1001
Add user and group to LDAP database (Optional)
Add the users and groups to the ldap directory using the below commands
[root@ldap-client ~]# ldapadd -f testuser1.ldif -x -D cn=admin,dc=example,dc=com -w redhat adding new entry "uid=testuser1,ou=users,dc=example,dc=com" [root@ldap-client ~]# ldapadd -x -D cn=admin,dc=example,dc=com -f groups.ldif -w redhat adding new entry "cn=testuser1,ou=users,dc=example,dc=com"
ldap_add: Invalid syntax (21); additional info: objectClass: value #0 invalid per syntax while executing above command then you must load nis.ldif using
# ldapadd -Y EXTERNAL -H ldapi:// -f /etc/openldap/schema/nis.ldif SASL/EXTERNAL authentication started SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth SASL SSF: 0 adding new entry "cn=nis,cn=schema,cn=config"
and then re-try the ldapadd command for user/group.
Validate the new user and group (Optional)
Run the ldapsearch command again and verify users and groups are listed under the base DN to complete the configuration.
[root@ldap-client ~]# ldapsearch -x -D cn=admin,dc=example,dc=com -b dc=example,dc=com -w redhat # extended LDIF # # LDAPv3 # base <dc=example,dc=com> with scope subtree # filter: (objectclass=*) # requesting: ALL # # example.com dn: dc=example,dc=com objectClass: dcObject objectClass: organization dc: example o: example # users, example.com dn: ou=users,dc=example,dc=com objectClass: organizationalUnit ou: users # scientists, users, example.com dn: cn=scientists,ou=users,dc=example,dc=com cn: scientists objectClass: groupOfNames member: cn=Archimedes of Syracuse,ou=users,dc=example,dc=com # testuser1, users, example.com dn: uid=testuser1,ou=users,dc=example,dc=com uid: testuser1 cn: testuser1 objectClass: shadowAccount objectClass: top objectClass: person objectClass: inetOrgPerson objectClass: posixAccount userPassword:: e1NTSEF9NXJNTS8zZjhLaTEzSXlhckdUdHd6aWVvVHU3S01nd2M= shadowLastChange: 17016 shadowMin: 0 shadowMax: 99999 shadowWarning: 7 loginShell: /bin/bash uidNumber: 1001 gidNumber: 1001 homeDirectory: /home/testuser1 sn: testuser1 mail: testuser1@example.com # testuser1, users, example.com dn: cn=testuser1,ou=users,dc=example,dc=com objectClass: posixGroup objectClass: top cn: testuser1 userPassword:: e2NyeXB0fXg= gidNumber: 1001 # search result search: 2 result: 0 Success # numResponses: 6 # numEntries: 5
Connect via LDAP User
Since we have installed oddjob, so we don't need to create ldap user's home directory manually and it will created during the first login of the user. Now we’ll be able to authenticate with an LDAP user
login as: testuser1
testuser1@10.0.2.13's password:
[testuser1@ldap-client ~]$
Conclusion
In this tutorial I shared the step by step instructions to configure LDAP client using RHEL/CentOS 7 Linux server. Additionally I have also shared the commands to create ldap user and group which you can use to verify your configuration. Since we are using oddjob, we don't have the dependency to create ldap user's home directory manually any more.
Lastly I hope the steps from the article to Configure LDAP client to authenticate with LDAP server on Linux was helpful. So, let me know your suggestions and feedback using the comment section.
References
I have used below external references for this tutorial guide
Learn CentOS Linux Network Services
how do i login user but it creates the home directory on login so i dont have to create home directory for users everytime manually ?
This seems to be a known problem with some hacks
You can check https://unix.stackexchange.com/questions/206110/openldap-how-to-add-home-directory-for-users if it helps
Amazing post, many thanks!
Whether to increase “ldapadd -Y EXTERNAL -H ldapi:// -f /etc/openldap/schema/nis.ldif” for “objectClass: shadowAccount” about testuser1.ldif
THANK YOU!!!!
Following ubuntu tutorials for days did not work and it probably had something to do with the cert creation process (openssl vs certtool).
i have follow all step but i cannot find user in getent passwd , and still access denied or permisiion denied while ssh or su haryo
but shown like this if command getent passwd haryo:
haryo:*:1001:1001:haryo:/home/haryo:/bin/bash
this * should be x
hello, thank you for the post.
i have a few question:
1- For the file: /etc/openldap/openldap.conf you say:
“Here comment out TLS_CACERTDIR and add TLS_REQCERT never”
So, how is ldap client going to find certification?
2 – for this part ” Create LDAP user..” until the end:
why do we have to create the user in LDAP client? isn’t the main point of LDAP that you shouldn’t create the user in each client, but create it on the server and login on the client?
thank you
Hello Briseida,
I had commented out TLS_CACERTDIR just in case the same entry exists in out config file then it may create conflice but if we are using the default path then that should not be a problem.
TLS_REQCERT parameter that indicates how strict the client needs are to enforce TLS security. We set it to never to bypass any problems that are related to TLS certificate features. You can also use allow in which case the client requests a server certificate, but if no valid certificate is provided, the session proceeds normally.
The steps to create user and group is just to illustrate that now using client you can add a user to ldap database and the same user can be used to log in on any other valid client.
Hi,
What all files authconfig-tui / authconfig tool will modify?
Hi Riyaz, I am afraid I will also have to analyse this area as have not checked this. If you come to know please do share with me as well
It’s hard to find experienced people in this particular topic,
however, you sound like you know what you’re talking about!
Thanks
Hello , thankd for the tuto.
However:
“Connect via LDAP User”
what is the shell command for that ?
I am trying ssh user1@myserver.mydoamain.com
and i keep getting “permission denied” and “publickey,gssapi-keyex,gssapi-with-mic,password”
Ldapsearch and so on seems fine though.
Any idea ? Thanks!
Hello, Can you please check on the myserver.mydoamain.com server is user exists (just to be sure). If yes then you can monitor the sshd logs from /var/log/messages or /var/log/sshd on this node (in RHEL 7 I prefer journalctl -f) and then attempt to do SSH. It may give more hint for the next places to look into..
You can also try a normal “su – user” on the myserver.mydomain.com if that works, as that way we know the problem is with SSHD
Hope this helps..
– Step-by-Step Tutorial: Configure OpenLDAP with TLS certificates CentOS 7 Linux
[root@ldap-server CA]# cp -v certs/ca.cert.pem /etc/openldap/cacerts/
‘certs/ca.cert.pem’ -> ‘/etc/openldap/cacerts/ca.cert.pem’
– Step-by-Step Tutorial: Configure LDAP client to authenticate with LDAP server
Next copy /etc/openldap/cacerts/ca.key.pem from the ldap-server to ldap-client in the same location under /etc/openldap/cacerts/ca.key.pem.
Question:
‘/etc/openldap/cacerts/ca.cert.pem’ /etc/openldap/cacerts/ca.key.pem
Sorry, I did not understood your question.
The qustion is:
In previous post “Step-by-Step Tutorial: Configure OpenLDAP with TLS certificates CentOS 7 Linux”, you wrote to “cp -v certs/ca.cert.pem /etc/openldap/cacerts/” . So the only file in /etc/openldap/cacert is “ca.cert.pem”
In this post you tell us to copy the “/etc/openldap/cacert/ca.key.pem” from ldap server, but it doesn’t exist.
So which file must exist in client /etc/openldap/caccert, ca.key.pem ? from where ?
or ca.cert.pem ?
Good job ! It is the first time I make a CA.
Thank you for your feedback. I have corrected the typo, it should be ca.cert.pem