Active Directory Integration

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This guide explains how to include Arch Linux into an existing Windows Active Directory.

Preface

Although I have tested this HowTo many times, there may still be bugs. This procedure worked this week, but who knows if it will do tomorrow; any update to glibc, Samba, or heimdal could break this HowTo into pieces.

Having backups of all modified files is recommended, as well as testing local login before any rebooting. In the worst case scenario, login will be broken for all users, including root - so be warned: Don't reboot or logout as root until you have checked everything.

Do not rely upon any information found in this guide without independent verification -- use at own risk.

General

  • What you get:
    • Windows AD users & Arch Linux users are accepted Arch Linux box users, at the console or gdm
    • Windows AD users can use Samba shares like shared Windows files.
  • What you won't get
    • Windows users are simply users on your machine. Possibly you can have Windows AD Admins to be linux admins, too. But this is not worked out so far in this HowTo.
    • Several other apps use authentication - like sudo, f.e. As far as they use PAM, it should be able to let them check against AD user accounts, too. But this is not worked out so far.

Requirements

  • Have a Windows Active Directory (AD)
  • Have Network Admin privileges.
  • Have access to the root account.
  • Have the ability to comfortably work within Linux without X.org.

Note: There is NO need to taint the AD with Linux schemes.

Preparation of the Windows AD policy

It is necessary to disable Digital Sign Communication (Always) in the AD group policies. Dive into:

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)

This is all you have to do in Windows. Let's go on with Arch Linux.

Installation

These packages are needed on the Arch Linux machine:

  • Samba
  • NTP
  • Heimdal
  • pam_pwcheck
  • pam_krb5.so

All of the packages can be installed by using pacman:

pacman -S samba ntp heimdal pam_pwcheck pam-krb5

Configuration

Please check your /etc/hosts file! It is important for it to be correctly configured. If you have a dual boot system on a machine, you have to use a different hostname and netbios name for the linux configuration, or the protected connection between windows and the domain controller will result broken.

In our example:
127.0.0.1 MACHINE-NAME.PARADISE.COM MACHINE-NAME
192.168.0.1 ADAM.PARADISE.COM ADAM
192.168.0.2 EVE.PARADISE.COM EVE

Samba / Winbindd startup

Arch Linux implements samba and winbind as a single script in /etc/rc.d/samba

The daemons started by /etc/rc.d/samba are configured in the file /etc/conf.d/samba.

##### /etc/conf.d/samba #####
#SAMBA_DAEMONS=(smbd nmbd)
SAMBA_DAEMONS=(smbd nmbd winbindd)

Heimdal / Kerberos - /etc/krb5.conf

Let's assume that your AD is named paradise.com. Let's further assume your AD is ruled by two domain controllers, the primary and secondary one, which are named adam and eve, adam.paradise.com and eve.paradise.com respectively. Their IP adresses will be 192.168.0.1 and 192.168.0.2 in this example. Take care to watch your syntax; upper-case is very important here.

##### /etc/krb5.conf ####
[libdefaults]
        default_realm 	= 	PARADISE.COM
	clockskew 	= 	300
	ticket_lifetime	=	1d
	
[realms]
	PARADISE.COM = {
		kdc 	= 	192.168.0.1
		kdc 	= 	192.168.0.2
		default_domain = PARADISE.COM
	}
	
	
[domain_realm]
	.paradise.com 	= 	PARADISE.COM
	paradise.com	= 	PARADISE.COM
	paradise	= 	PARADISE.COM

[appdefaults]
	pam = {
	ticket_lifetime 	= 1d
	renew_lifetime 		= 1d
	forwardable 		= true
	proxiable 		= false
	retain_after_close 	= false
	minimum_uid 		= 0
	debug 			= false
	}

[logging]
	default 		= SYSLOG:NOTICE:DAEMON
	kdc 			= FILE:/var/log/kdc.log 

Update:

Heimdal 1.3.1 deprecated DES encryption which is required for AD authentication before Windows Server 2008. You'll probably have to add
allow_weak_crypto = true
to the [libdefaults] section.


Inside an AD, it is important that all machines run the same system time. To synchronize the time run:

/usr/bin/ntpdate adam.paradise.com

Now you can query the AD domain controllers for a ticket with the following commands (uppercase is necessary):

# kinit ADMINISTRATOR@PARADISE.COM

You´ll now be asked for the password. In case it matches, you'll be returned to the console.

PAM configuration for login

Now we have to change /etc/pam.d/login so it sends its request to the AD controllers. 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_winbindd.so into the authentication process. Furthermore, we include pam_mkhomedir.so. If an AD user logs in, /home/paradise/user will be created automatically.

#### /etc/pam.d/login ####
#%PAM-1.0
auth     sufficient     pam_unix2.so
auth     required       pam_winbind.so use_first_pass use_authtok
auth     required       pam_securetty.so
auth     required       pam_nologin.so
auth     required       pam_mail.so
account  sufficient     pam_unix2.so
account  sufficient     pam_winbind.so use_first_pass use_authtok
password required       pam_pwcheck.so
password sufficient     pam_unix2.so
password sufficient     pam_winbind.so use_first_pass use_authtok
session  required       pam_mkhomedir.so skel=/etc/skel/ umask=0022
session  sufficient     pam_unix2.so
session  sufficient     pam_winbind.so use_first_pass use_authtok
session  required       pam_limits.so

If you like to allow AD users to login into GDM, you have to do the same for /etc/pam.d/gdm. You may try to change other /etc/pam.d/ rules for other apps, to allow them to authenticate AD users.

Samba configuration for shares

Samba is highly configurable. Take this example only as a rough idea, hardly polished. Here is what my /etc/samba/smb.conf looks like:

#### /etc/samba/smb.conf ####
[Global]
netbios name = archlinux
workgroup = PARADISE
realm = PARADISE.COM
server string = archlinux
map to guest = Bad User
idmap uid = 10000-20000
idmap gid = 10000-20000
winbind enum users = yes
winbind enum groups = yes
winbind gid = 10000-20000
winbind use default domain = Yes
winbind separator =+
os level = 20

# Theres no shell defined for users in AD, so I define a default shell to use
# Not sure if its even possible to define a shell in AD
template shell = /bin/bash
 
encrypt passwords = yes
security = ads
password server = adam.paradise.com
preferred master = no
dns proxy = no
wins server = eve.paradise.com
wins proxy = no

admin users = @"NET+domain admins"
force group = "PARADISE+domain admins"
inherit acls = Yes
map acl inherit = Yes
acl group control = yes

load printers = no
debug level = 3
use sendfile = no
 
[homes]
comment = User´s homedirs
path =/home/%U
valid users = %S NET+%S
browseable = no
read only = no

[data]  
comment = Data
valid users = %S net+%S
path = /data
read only = no
browseable = yes
 
[Back-up]
comment = Backup filer
path = /backup
read only = no
browseable = yes
valid users = @"NET+Domain Admins"

We shall now explain to Samba that it shall use the PDC´s database for authentication queries. Again, we use winbindd which is a part of the samba package. Winbind maps the UID and GID of the AD to our Linux-machine. Winbind uses a Unix-implementation of RPC-calls, Pluggable Authentication Modules (aka PAM) and Name Service Switch (NSS) to allow Windows AD and users accessing and to grant permissions on the Linux-machine. The best part of winbindd is, that you don´t have to define the mapping yourself, but only define a range of UID and GID. That´s what we defined in smb.conf. To include Winbindd into NSS calls, edit /etc/nsswitch.conf. Add winbind to the lines as shown here:

#### /etc/nsswitch.conf ####
passwd:            files winbind
shadow:            files winbind
group:             files winbind

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.

Start Samba (including smbd, nmbd and winbindd:

/etc/rc.d/samba restart

Testing Winbind

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

wbinfo -u

We can do the same for AD groups:

wbinfo -g

Testing login

Now, start a new console session and try to login with an AD account. As we told winbind to use default_realms, it should not be necessary to add the AD name. Lets assume there is an AD user named kain. Try to login as

kain
PARADISE+kain

Both should work. You should notice that /home/paradise/kain will be 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!

Testing Samba commands

Try out some net commands to see if samba can address the AD:

net ads info
net ads lookup
net ads status

The commands return several AD related information.

Arch Linux becomes an AD member

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

# net ads join -U Administrator
Administrator's password: xxx
Using short domain name -- PARADISE
Joined 'MACHINE-NAME' to realm 'PARADISE.COM'

When to reboot?

Everything checked? OK. Pray and reboot.

Resources

Everything there is to know about Samba

Please feel free to comment this article - but if your edit this - PLEASE LET ME KNOW