Ninama

From Wikipedia:

1. Ldap Server Active Directory
2. How Ldap Works With Active Directory
3. Difference Between Ldap And Active Directory
4. Authentication Through Active Directory

Active Directory (AD) is a directory service that Microsoft developed for Windows domain networks.

This article describes how to integrate an Arch Linux system with an existing Windows domain network using Samba.

Before continuing, you must have an existing Active Directory domain, and have a user with the appropriate rights within the domain to: query users and add computer accounts (Domain Join).

This document is not an intended as a complete guide to Active Directory nor Samba. Refer to the resources section for additional information.

1. The UnboundID LDAP SDK provides classes to create an in-memory LDAP server. This method has the advantage of not having to install and maintain a server. This method has the advantage of not having to install and maintain a server.
2. LDAP is a way of speaking to Active Directory. LDAP is a protocol that many different directory services and access management solutions can understand. The relationship between AD and LDAP is much like the relationship between Apache and HTTP: HTTP is a web protocol. Apache is a web server that uses the HTTP protocol. LDAP is a directory services protocol. Active Directory is a directory server that uses the LDAP protocol.

Active Directory serves as a central location for network administration and security. It is responsible for authenticating and authorizing all users and computers within a Windows domain network, assigning and enforcing security policies for all computers in a network and installing or updating software on network computers. For example, when a user logs into a computer that is part of a Windows domain, it is Active Directory that verifies his or her password and specifies whether he or she is a system administrator or normal user. Server computers on which Active Directory is running are called domain controllers.

Active Directory uses Lightweight Directory Access Protocol (LDAP) versions 2 and 3, Microsoft's version of Kerberos and DNS.

How to view and set LDAP policy in Active Directory by using Ntdsutil.exe Content provided by Microsoft Applies to: Windows Server Datacenter Core, version 1809. How to setup LDAP authentication to an Active Directory LDAP database. This article explains the steps needed to perform in order to set AXIGEN domain users authenticate to an Active Directory LDAP database. YourChosenName This will be used to set in the configuration of the services you want to login to active directory. Setting Up LDAP and Active Directory. Overview of Directory Integration Steps To set up directory server integration, you need to gather information about your LDAP server configuration, identify the location of your key directory server and tree, map your users and (optionally) groups so Jive can synchronize to them, and then test your. Use these topics to assist you in setting up user authentication using Microsoft's LDAP-based Active Directory product. This procedure uses the TEPS/e Web browser interface to complete the portal server configuration; see Using the TEPS/e administration console. Configuring the portal server to use.

• 2Active Directory configuration
• 3Linux host configuration
  • 3.4Kerberos
• 4Starting and testing services
• 5Configuring PAM
  • 5.1system-auth
  • 5.2passwd
• 7Adding a machine keytab file and activating password-free kerberized ssh to the machine
• 8Generating user Keytabs which are accepted by AD
• 9See also

Terminology

If you are not familiar with Active Directory, there are a few keywords that are helpful to know.

• Domain : The name used to group computers and accounts.
• SID : Each computer that joins the domain as a member must have a unique SID or System Identifier.
• SMB : Server Message Block.
• NETBIOS: Network naming protocol used as an alternative to DNS. Mostly legacy, but still used in Windows Networking.
• WINS: Windows Information Naming Service. Used for resolving Netbios names to windows hosts.
• Winbind: Protocol for windows authentication.

Active Directory configuration

This section works with the default configuration of Windows Server 2012 R2.

GPO considerations

Digital signing is enabled by default in Windows Server, and must be enabled at both the client and server level. For certain versions of Samba, Linux clients may experience issues connecting to the domain and/or shares. It's recommended you add the following parameters to your smb.conf file:

If that is not successful, you can disable Digital Sign Communication (Always) in the AD group policies. In your AD Group Policy editor, locate:

Under Local policies > Security policies > Microsoft Network Server > Digital sign communication (Always) activate define this policy and use the disable radio button.

If you use Windows Server 2008 R2, you need to modify that in GPO for Default Domain Controller Policy > Computer Setting > Policies > Windows Setting > Security Setting > Local Policies > Security Option > Microsoft network client: Digitally sign communications (always).

Please note that disabling this GPO affects the security of all members of the domain.

Linux host configuration

The next few steps will begin the process of configuring the Host. You will need root or sudo access to complete these steps.

Installation

Install the following packages:

• samba, see also Samba
• ntp or openntpd, see also NTPd or OpenNTPD

Updating DNS

Active Directory is heavily dependent upon DNS. You will need to update /etc/resolv.conf to use one or more of the Active Directory domain controllers:

Replacing <IP1> and <IP2> with valid IP addresses for the AD servers. If your AD domains do not permit DNS forwarding or recursion, you may need to add additional resolvers.

Configuring NTP

Read System time#Time synchronization to configure an NTP service.

On the NTP servers configuration, use the IP addresses for the AD servers, as they typically run NTP as a service. Alternatively, you can use other known NTP servers provided the Active directory servers sync to the same stratum.

Ensure that the service is configured to sync the time automatically very early on startup.

Kerberos

Let us assume that your AD is named example.com. Let us further assume your AD is ruled by two domain controllers, the primary and secondary one, which are named PDC and BDC, pdc.example.com and bdc.example.com respectively. Their IP adresses will be 192.168.1.2 and 192.168.1.3 in this example. Take care to watch your syntax; upper-case is very important here.

Creating a Kerberos ticket

Now you can query the AD domain controllers and request a kerberos ticket (uppercase is necessary):

You can use any username that has rights as a Domain Administrator.

Validating the Ticket

Run klist to verify you did receive the token. You should see something similar to:

pam_winbind.conf

If you get errors stating that /etc/security/pam_winbind.conf was not found, create the file and add the following:

With this setup, winbind will create user keytabs on the fly (krb5_ccache_type = FILE) at login and maintain them. You can verify this by simply running klist in a shell after logging in as an AD user but without needing to run kinit. You may need to set additional permissions on /etc/krb5.keytab eg 640 instead of 600 to get this to work (see FS#52621 for example)

Samba

Samba is a free software re-implementation of the SMB/CIFS networking protocol. It also includes tools for Linux machines to act as Windows networking servers and clients.

In this section, we will focus on getting Authentication to work first by editing the 'Global' section first. Later, we will go back and add shares.

Join the domain

You need an AD Administrator account to do this. Let us assume this is named Administrator. The command is 'net ads join'

Starting and testing services

Starting Samba

Hopefully, you have not rebooted yet! Fine. If you are in an X-session, quit it, so you can test login into another console, while you are still logged in.

Enable and start the individual Samba daemons smbd.service, nmbd.service, and winbindd.service.

Next we will need to modify the NSSwitch configuration, which tells the Linux host how to retrieve information from various sources and in which order to do so. In this case, we are appending Active Directory as additional sources for Users, Groups, and Hosts.

Testing Winbind

Let us check if winbind is able to query the AD. The following command should return a list of AD users:

• Note we created an Active Directory user called 'test.user' on the domain controller

We can do the same for AD groups:

Testing nsswitch

To ensure that our host is able to query the domain for users and groups, we test nsswitch settings by issuing the 'getent' command.

If user accounts from your DC are not showing, try adding the following line to your smb.conf file:

The following output shows what a stock ArchLinux install looks like:

And for groups:

Testing Samba commands

Try out some net commands to see if Samba can communicate with AD:

Configuring PAM

Now we will change various rules in PAM to allow Active Directory users to use the system for things like login and sudo access. When changing the rules, note the order of these items and whether they are marked as required or sufficient is critical to things working as expected. You should not deviate from these rules unless you know how to write PAM rules.

In case of logins, PAM should first ask for AD accounts, and for local accounts if no matching AD account was found. Therefore, we add entries to include pam_winbind.so into the authentication process.

The Arch Linux PAM configuration keeps the central auth process in /etc/pam.d/system-auth. Starting with the stock configuration from pambase, change it like this:

system-auth

'auth' section

Find the line:

Delete it, and replace with:

'account' section

Find the line:

Keep it, and add this below:

'password' section

Find the line:

Delete it, and replace with:

'session' section

Find the line:

Keep it, and add this line immediately above it:

Below the pam_unix line, add these:

passwd

'password' section

In order for logged-in Active Directory users to be able to change their passwords with the 'passwd' command, the file /etc/pam.d/passwd must include the information from system-auth.

Find the line:

Delete it, and replace with:

Testing login

Now, start a new console session (or ssh) and try to login using the AD credentials. The domain name is optional, as this was set in the Winbind configuration as 'default realm'. Please note that in the case of ssh, you will need to modify the /etc/ssh/sshd_config file to allow kerberos authentication (KerberosAuthentication yes).

Both should work. You should notice that /home/example/test.user will be automatically created.Log into another session using an linux account. Check that you still be able to log in as root - but keep in mind to be logged in as root in at least one session!

Configuring Shares

Earlier we skipped configuration of the shares. Now that things are working, go back to /etc/samba/smb.conf, and add the exports for the host that you want available on the windows network.

In the above example, the keyword NETWORK is to be used. Do not mistakenly substitute this with your domain name. For adding groups, prepend the '@' symbol to the group. Note that Domain Admins is encapsulated in quotes so Samba correctly parses it when reading the configuration file.

Adding a machine keytab file and activating password-free kerberized ssh to the machine

This explains how to generate a machine keytab file which you will need e.g. to enable password-free kerberized ssh to your machine from other machines in the domain. The scenario in mind is that you have a bunch of systems in your domain and you just added a server/workstation using the above description to your domain onto which a lot of users need to ssh in order to work - e.g. GPU workstation or an OpenMP compute node, etc. In this case you might not want to type your password every time you log in. On the other hand the key authentication used by many users in this case can not give you the necessary credentials to e.g. mount kerberized NFSv4 shares. So this will help you to enable password-free logins from your clients to the machine in question using kerberos ticket forwarding.

Creating a machine key tab file

run 'net ads keytab create -U administrator' as root to create a machine keytab file in /etc/krb5.keytab. It will prompt you with a warning that we need to enable keytab authentication in our configuration file, so we will do that in the next step. In my case it had problems when a key tab file is already in place - the command just did not come back it hang ... In that case you should rename the existing /etc/krb5.keytab and run the command again - it should work now.

verify the content of your keytab by running:

Enabling keytab authentication

Now you need to tell winbind to use the file by adding these lines to the /etc/samba/smb.conf:

It should look something like this:

Restart the winbind daemon using 'systemctl restart winbindd.service' with root privileges.

Check if everything works by getting a machine ticket for your system by running

This should not give you any feedback but running 'klist' should show you sth like:

Some common mistakes here are a) forgetting the trailing $ or b) ignoring case sensitivity - it needs to look exactly like the entry in the keytab (usually you cannot to much wrong with all capital)

Preparing sshd on server

All we need to do is add some options to our sshd_config and restart the sshd.service.

Ldap Server Active Directory

Edit /etc/ssh/sshd_config to look like this in the appropriate places:

Restart the sshd.service using:

Adding necessary options on client

First we need to make sure that the tickets on our client are forwardable. This is usually standard but we better check anyways. You have to look for the forwardable option and set it to 'true' in the Kerberos config file /etc/krb5.conf

Secondly we need to add the options

to our .ssh/config file to tell ssh to use this options - alternatively they can be invoked using the -o options directly in the ssh command (see 'man ssh' for help).

Testing the setup

On Client:

make sure you have a valid ticket - if in doubt run 'kinit'

then use ssh to connect to you machine

you should get connected without needing to enter your password.

if you have key authentication additionally activated then you should perform

to see which authentication method it actually uses.

For debugging you can enable DEBUG3 on the server and look into the journal using journalctl.

Nifty fine-tuning for complete password-free kerberos handling.

In case your clients are not using domain accounts on their local machines (for whatever reason) it can be hard to actually teach them to kinit before ssh to the workstation. Therefore I came up with a nice workaround:

Generating user Keytabs which are accepted by AD

On a system let the user run:

Now test the file by invoking:

It should not promt you to give your password nor should it give any other feedback. If it worked you are basically done - just put the line above into your ~./bashrc - you can now get kerberos tickets without typing a password and with that you can connect to your workstation without typing a password while being completely kerberized and able to authenticate against NFSv4 and CIFS via tickets - pretty neat.

Nice to know

The file 'username.keytab' is not machinespecific and can therefore be copied around. E.g. we created the files on a linux machine and copied them to our Mac clients as the commands on Macs are different ...

How Ldap Works With Active Directory

See also

Commercial Solutions

• Centrify
• Likewise

OpenSource version

Difference Between Ldap And Active Directory

• PowerBroker Identity Services Open: formerly Likewise acquired by BeyondTrust

Authentication Through Active Directory