OpenLDAP backend (legacy)

Note:
This section is flagged as legacy because nowadays, Samba 4 is best integrated with its own LDAP server in Active Directory mode. Integrating Samba with LDAP as described here covers the NT4 mode, which has been deprecated for many years.

This section covers the integration of Samba with LDAP. The Samba server’s role will be that of a “standalone” server and the LDAP directory will provide the authentication layer in addition to containing the user, group, and machine account information that Samba requires in order to function (in any of its 3 possible roles). The pre-requisite is an OpenLDAP server configured with a directory that can accept authentication requests. See Install LDAP and LDAP with Transport Layer Security for details on fulfilling this requirement. Once those steps are completed, you will need to decide what specifically you want Samba to do for you and then configure it accordingly.

This guide will assume that the LDAP and Samba services are running on the same server and therefore use SASL EXTERNAL authentication whenever changing something under cn=config. If that is not your scenario, you will have to run those LDAP commands on the LDAP server.

Install the software

There are two packages needed when integrating Samba with LDAP: samba and smbldap-tools.

Strictly speaking, the smbldap-tools package isn’t needed, but unless you have some other way to manage the various Samba entities (users, groups, computers) in an LDAP context then you should install it.

Install these packages now:

sudo apt install samba smbldap-tools

Configure LDAP

We will now configure the LDAP server so that it can accommodate Samba data. We will perform three tasks in this section:

Import a schema
Index some entries
Add objects

Samba schema

In order for OpenLDAP to be used as a backend for Samba, the DIT will need to use attributes that can properly describe Samba data. Such attributes can be obtained by introducing a Samba LDAP schema. Let’s do this now.

The schema is found in the now-installed samba package and is already in the LDIF format. We can import it with one simple command:

sudo ldapadd -Q -Y EXTERNAL -H ldapi:/// -f /usr/share/doc/samba/examples/LDAP/samba.ldif

To query and view this new schema:

sudo ldapsearch -Q -LLL -Y EXTERNAL -H ldapi:/// -b cn=schema,cn=config 'cn=*samba*'

Samba indices

Now that slapd knows about the Samba attributes, we can set up some indices based on them. Indexing entries is a way to improve performance when a client performs a filtered search on the DIT.

Create the file samba_indices.ldif with the following contents:

dn: olcDatabase={1}mdb,cn=config
changetype: modify
replace: olcDbIndex
olcDbIndex: objectClass eq
olcDbIndex: uidNumber,gidNumber eq
olcDbIndex: loginShell eq
olcDbIndex: uid,cn eq,sub
olcDbIndex: memberUid eq,sub
olcDbIndex: member,uniqueMember eq
olcDbIndex: sambaSID eq
olcDbIndex: sambaPrimaryGroupSID eq
olcDbIndex: sambaGroupType eq
olcDbIndex: sambaSIDList eq
olcDbIndex: sambaDomainName eq
olcDbIndex: default sub,eq

Using the ldapmodify utility load the new indices:

sudo ldapmodify -Q -Y EXTERNAL -H ldapi:/// -f samba_indices.ldif

If all went well you should see the new indices when using ldapsearch:

sudo ldapsearch -Q -LLL -Y EXTERNAL -H \
ldapi:/// -b cn=config olcDatabase={1}mdb olcDbIndex

Adding Samba LDAP objects

Next, configure the smbldap-tools package to match your environment. The package comes with a configuration helper script called smbldap-config. Before running it, though, you should decide on two important configuration settings in /etc/samba/smb.conf:

netbios name
How this server will be known. The default value is derived from the server’s hostname, but truncated at 15 characters.
workgroup
The workgroup name for this server, or, if you later decide to make it a domain controller, this will be the domain.

It’s important to make these choices now because smbldap-config will use them to generate the config that will be later stored in the LDAP directory. If you run smbldap-config now and later change these values in /etc/samba/smb.conf there will be an inconsistency.

Once you are happy with netbios name and workgroup, proceed to generate the smbldap-tools configuration by running the configuration script which will ask you some questions:

sudo smbldap-config

Some of the more important ones:

workgroup name
Has to match what you will configure in /etc/samba/smb.conf later on.
ldap suffix
Has to match the LDAP suffix you chose when you configured the LDAP server.
other ldap suffixes
They are all relative to ldap suffix above. For example, for ldap user suffix you should use ou=People, and for computer/machines, use ou=Computers.
ldap master bind dn and bind password
Use the Root DN credentials.

The smbldap-populate script will then add the LDAP objects required for Samba. It will ask you for a password for the “domain root” user, which is also the “root” user stored in LDAP:

sudo smbldap-populate -g 10000 -u 10000 -r 10000

The -g, -u and -r parameters tell smbldap-tools where to start the numeric uid and gid allocation for the LDAP users. You should pick a range start that does not overlap with your local /etc/passwd users.

You can create a LDIF file containing the new Samba objects by executing sudo smbldap-populate -e samba.ldif. This allows you to look over the changes making sure everything is correct. If it is, rerun the script without the '-e' switch. Alternatively, you can take the LDIF file and import its data as per usual.

Your LDAP directory now has the necessary information to authenticate Samba users.

Samba configuration

To configure Samba to use LDAP, edit its configuration file /etc/samba/smb.conf commenting out the default passdb backend parameter and adding some LDAP-related ones. Make sure to use the same values you used when running smbldap-populate:

#  passdb backend = tdbsam
workgroup = EXAMPLE
    
# LDAP Settings
passdb backend = ldapsam:ldap://ldap01.example.com
ldap suffix = dc=example,dc=com
ldap user suffix = ou=People
ldap group suffix = ou=Groups
ldap machine suffix = ou=Computers
ldap idmap suffix = ou=Idmap
ldap admin dn = cn=admin,dc=example,dc=com
ldap ssl = start tls
ldap passwd sync = yes

Change the values to match your environment.

Note:
The smb.conf as shipped by the package is quite long and has many configuration examples. An easy way to visualise it without any comments is to run testparm -s.

Now inform Samba about the Root DN user’s password (the one set during the installation of the slapd package):

sudo smbpasswd -W

As a final step to have your LDAP users be able to connect to Samba and authenticate, we need these users to also show up in the system as “Unix” users. Use SSSD for that as detailed in Network User Authentication with SSSD.

Install sssd-ldap:

sudo apt install sssd-ldap

Configure /etc/sssd/sssd.conf:

[sssd]
config_file_version = 2
domains = example.com

[domain/example.com]
id_provider = ldap
auth_provider = ldap
ldap_uri = ldap://ldap01.example.com
cache_credentials = True
ldap_search_base = dc=example,dc=com

Adjust permissions and start the service:

sudo chmod 0600 /etc/sssd/sssd.conf
sudo chown root:root /etc/sssd/sssd.conf
sudo systemctl start sssd

Restart the Samba services:

sudo systemctl restart smbd.service nmbd.service

To quickly test the setup, see if getent can list the Samba groups:

$ getent group Replicators
Replicators:*:552:

Note:
The names are case sensitive!

If you have existing LDAP users that you want to include in your new LDAP-backed Samba they will, of course, also need to be given some of the extra Samba specific attributes. The smbpasswd utility can do this for you:

sudo smbpasswd -a username

You will be prompted to enter a password. It will be considered as the new password for that user. Making it the same as before is reasonable. Note that this command cannot be used to create a new user from scratch in LDAP (unless you are using ldapsam:trusted and ldapsam:editposix, which are not covered in this guide).

To manage user, group, and machine accounts use the utilities provided by the smbldap-tools package. Here are some examples:

To add a new user with a home directory:
```
sudo smbldap-useradd -a -P -m username
```
The -a option adds the Samba attributes, and the -P option calls the smbldap-passwd utility after the user is created allowing you to enter a password for the user. Finally, -m creates a local home directory. Test with the getent command:
```
getent passwd username
```
To remove a user:
```
sudo smbldap-userdel username
```
In the above command, use the -r option to remove the user’s home directory.
To add a group:
```
sudo smbldap-groupadd -a groupname
```
As for smbldap-useradd, the -a adds the Samba attributes.
To make an existing user a member of a group:
```
sudo smbldap-groupmod -m username groupname
```
The -m option can add more than one user at a time by listing them in comma-separated format.

To remove a user from a group:

sudo smbldap-groupmod -x username groupname

To add a Samba machine account:
```
sudo smbldap-useradd -t 0 -w username
```
Replace username with the name of the workstation. The -t 0 option creates the machine account without a delay, while the -w option specifies the user as a machine account.

Resources

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