Active Directory Integration
This guide explains how to include ArchLinux into an existing Windows Active Directory.
THIS DOCUMENT IS A WORK IN PROGRESS
Contents
Introduction
A key challenge for system administrators of any datacenter is trying to coexisting in Heterogeneous environments. By this we mean the mixing of different server operating system technologies (typicall Microsoft Windows & Unix/Linux). User management and authentication is by far the most difficult of these to solve. The most common way of solving this problem is to use a Directory Server. There are a number of open-source and commercial solutions for the various flavors of *NIX; however, few solve the problem of interoperating with Windows. Active Directory (AD) is a directory service created by Microsoft for Windows domain networks. It is included in most Windows Server operating systems. Server computers on which Active Directory is running are called domain controllers.
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 network of Windows domain type, 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.[1]
Active Directory uses Lightweight Directory Access Protocol (LDAP) versions 2 and 3, Kerberos and DNS. These same standards are available as linux, but piecing them together is not an easy task. Following these steps will help you configure an ArchLinux host to authenticate against an AD domain.
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).
AD Basic Terminology
If you are not familiar with Active Directory, there are a few keywords that must be understood. * This document is not an inclusive guide, refer to the resources section for additional information.
- 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.
Active Directory Configuration
NOTE: This section has not been validated. Proceed with caution
Updating the GPO
NOTE: These steps has not been validated. Proceed with caution
It may be 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)
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.
Arch Linux Packages
The following packages should also be installed:
- samba
- krb-5
- pam-krb5
- pam_pwcheck
- openntpd (or) ntp
pacman -S samba pam-krb5 pam_pwcheck 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:
nameserver <IP1> nameserver <IP2>
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.
Important: If your machine dual boots Windows and Linux, you should use a different DNS hostname and netbios name for the linux configuration if both operating systems will be members of the same domain.
Configuring NTP
In this example, we use OpenNTPD instead of ISC NTP. You may choose either package, but openntpd is cleaner and easier to configure.
/etc/conf.d/openntpd
Ensure the daemon is configured to 'sync' automatically on startup by adding the '-s' paramater to the config:
PARAMS="-s"
/etc/ntpd.conf
servers <IP1> servers <IP2>
Replacing <IP1> and <IP2> with valid IP addresses for the AD servers. Alternatively, you can use other known NTP servers provided the Active directory servers sync to the same stratum. However, AD servers typically run NTP as a service.
/etc/rc.conf
Next, add 'openntpd' to the list of startup daemons in the ArchLinux configuration file:
DAEMONS=(!hwclock syslog-ng dbus network openntpd crond sshd)
- Note we place it AFTER 'network' and BEFORE 'crond'
Start openntpd
Start the NTP daemon to sync the time now.
rc.d start openntpd
Kerberos
Let's assume that your AD is named example.com. Let's 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.
/etc/krb5.conf
[libdefaults]
default_realm = EXAMPLE.COM
clockskew = 300
ticket_lifetime = 1d
forwardable = true
proxiable = true
dns_lookup_realm = true
dns_lookup_kdc = true
[realms]
EXAMPLE.COM = {
kdc = PDC.EXAMPLE.COM
admin_server = PDC.EXAMPLE.COM
default_domain = EXAMPLE.COM
}
[domain_realm]
.kerberos.server = EXAMPLE.COM
.example.com = EXAMPLE.COM
example.com = EXAMPLE.COM
example = EXAMPLE.COM
[appdefaults]
pam = {
ticket_lifetime = 1d
renew_lifetime = 1d
forwardable = true
proxiable = false
retain_after_close = false
minimum_uid = 0
debug = false
}
[logging]
default = FILE:/var/log/krb5libs.log
kdc = FILE:/var/log/kdc.log
admin_server = FILE:/var/log/kadmind.log
Note:
allow_weak_crypto = trueto the
[libdefaults] section.
Creating a Kerberos Ticket
Now you can query the AD domain controllers and request a kerberos ticket (uppercase is necessary):
kinit administrator@EXAMPLE.COM
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:
# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: administrator@EXAMPLE.COM
Valid starting Expires Service principal
02/04/12 21:27:47 02/05/12 07:27:42 krbtgt/EXAMPLE.COM@EXAMPLE.COM
renew until 02/05/12 21:27:47
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.
/etc/samba/smb.conf
NOTE: The configuration can vary greatly depending on how the Windows environment is deployed. Be prepared to troubleshoot and research.
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.
[Global] netbios name = MYARCHLINUX workgroup = EXAMPLE realm = EXAMPLE.COM server string = %h ArchLinux Host security = ads encrypt passwords = yes password server = pdc.example.com idmapd uid = 10000-20000 idmapd gid = 10000-20000 #idmapd backend = rid winbind use default domain = Yes winbind enum users = Yes winbind enum groups = Yes winbind nested groups = Yes winbind separator = + winbind refresh tickets = yes winbind gid = 10000-20000 template shell = /bin/bash template homedir = /home/%D/%U preferred master = no dns proxy = no wins server = pdc.example.com wins proxy = no inherit acls = Yes map acl inherit = Yes acl group control = yes load printers = no debug level = 3 use sendfile = no
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.
/etc/conf.d/samba
Update the samba initscript configuration file to enable the winbind daemon
##### /etc/conf.d/samba ##### #SAMBA_DAEMONS=(smbd nmbd) SAMBA_DAEMONS=(smbd nmbd winbindd)
/etc/rc.conf
Next, add 'samba' to the list of startup daemons in the ArchLinux configuration file:
The daemons started by /etc/rc.d/samba are configured in the file /etc/conf.d/samba. * NOTE: Your actual list may vary.
DAEMONS=(hwclock syslog-ng dbus network openntpd crond sshd samba)
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
If you check the processes, you'll see that winbind did not actually start. A quick review of the logs shows that the SID for this host could be obtained from the domain:
# tail /var/log/samba/log.winbindd [2012/02/05 21:51:30.085574, 0] winbindd/winbindd_cache.c:3147(initialize_winbindd_cache) initialize_winbindd_cache: clearing cache and re-creating with version number 2 [2012/02/05 21:51:30.086137, 2] winbindd/winbindd_util.c:233(add_trusted_domain) Added domain BUILTIN S-1-5-32 [2012/02/05 21:51:30.086223, 2] winbindd/winbindd_util.c:233(add_trusted_domain) Added domain MYARCHLINUX S-1-5-21-3777857242-3272519233-2385508432 [2012/02/05 21:51:30.086254, 0] winbindd/winbindd_util.c:635(init_domain_list) Could not fetch our SID - did we join? [2012/02/05 21:51:30.086408, 0] winbindd/winbindd.c:1105(winbindd_register_handlers) unable to initialize domain list
Join the Domain
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'
Restart Samba
'winbindd' failed to start on the first try because we were not yet a domain. Restart the samba service and winbind should fire up as well:
rc.d restart samba
/etc/nsswitch.conf
NSSwitch 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.
passwd: files winbind shadow: files winbind group: files winbind hosts: files dns wins
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 Samba commands
Try out some net commands to see if samba can communicate with AD:
# net ads info [2012/02/05 20:21:36.473559, 0] param/loadparm.c:7599(lp_do_parameter) Ignoring unknown parameter "idmapd backend" LDAP server: 192.168.1.2 LDAP server name: PDC.example.com Realm: EXAMPLE.COM Bind Path: dc=EXAMPLE,dc=COM LDAP port: 389 Server time: Sun, 05 Feb 2012 20:21:33 CST KDC server: 192.168.1.2 Server time offset: -3
# net ads lookup
[2012/02/05 20:22:39.298823, 0] param/loadparm.c:7599(lp_do_parameter)
Ignoring unknown parameter "idmapd backend"
Information for Domain Controller: 192.168.1.2
Response Type: LOGON_SAM_LOGON_RESPONSE_EX
GUID: 2a098512-4c9f-4fe4-ac22-8f9231fabbad
Flags:
Is a PDC: yes
Is a GC of the forest: yes
Is an LDAP server: yes
Supports DS: yes
Is running a KDC: yes
Is running time services: yes
Is the closest DC: yes
Is writable: yes
Has a hardware clock: yes
Is a non-domain NC serviced by LDAP server: no
Is NT6 DC that has some secrets: no
Is NT6 DC that has all secrets: yes
Forest: example.com
Domain: example.com
Domain Controller: PDC.example.com
Pre-Win2k Domain: EXAMPLE
Pre-Win2k Hostname: PDC
Server Site Name : Office
Client Site Name : Office
NT Version: 5
LMNT Token: ffff
LM20 Token: ffff
net ads status
Configuring PAM for Logins
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/example/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.
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/example/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!
Earlier we skipped configuration of the shares. Now that things are working, go back to /etc/smb.conf, and add the exports for the host that you want available on the windows network.
[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"
Resources
- Wikipedia: Active Directory
- Wikipedia: Samba
- Wikipedia: Kerberos
- Samba: Documentation
- Samba Wiki: Samba & Active Directory
- Samba Man Page: smb.conf
Commercial Solutions
- Centrify
- Likewise