Active Directory integration

Related articles
Samba
Samba/Active Directory domain controller
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From
Wikipedia
:
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.
Introduction
This article explains how to configure an Arch Linux system to participate in an Active Directory domain. This article was written and tested on a fresh installation, and it is assumed that all configuration files are in their unmodified, post-installation state. For the duration of the article, the example Active Directory domain will use the following configuration:
NetBIOS domain name:
INTERNAL
DNS domain name:
internal.domain.tld
Kerberos realm:
INTERNAL.DOMAIN.TLD
First DC:
server1.internal.domain.tld
with IP address
192.168.1.1
Second DC:
server2.internal.domain.tld
with IP address
192.168.1.2
In most small networks, the DCs (domain controllers) also hold the DNS server role. This may not be true in larger networks. Generally, DCs also hold the NTP role, but not always. Consult your network administrator to verify correct values for DNS and NTP servers.
Needed software
In order to use samba effectively, you will need to install the following packages:
samba
,
smbclient
, and
ntp
. (
timedatectl
can be used as an alternative to
ntp
.)
Additionally, while not required, the following packages will be useful for testing and troubleshooting:
bind
,
krb5
, and if a printing is desired (whether you want to share printers, or use printers on another Samba/Windows host),
cups
.
Initial configuration of services
DNS configuration
Active Directory depends entirely on DNS for name resolution. It is imperative that the
/etc/resolv.conf
file is configured with both the correct DNS servers and a domain search suffix. Whether configured via DHCP or static configuration, ensure that these values are correct for your domain. For the example domain configuration, the following contents are appropriate (be sure to replace
192.168.1.1
,
192.168.1.2
, and
internal.domain.tld
with appropriate values for your network):
/etc/resolv.conf
nameserver
192.168.1.1
nameserver
192.168.1.2
search
internal.domain.tld
If you elected to install the
bind
package, you can test DNS configuration with the following commands (be sure to replace
server1
and
internal.domain.tld
with appropriate values for your network):
$ nslookup -type=SRV _kerberos._tcp.
internal.domain.tld
.
$ nslookup -type=SRV _ldap._tcp.
internal.domain.tld
.
$ nslookup
server1
.
internal.domain.tld
.
You should get output similar to the following (adjust appropriately for only one DC, or more than two):
Server:        192.168.1.1
Address:       192.168.1.1#53

_kerberos._tcp.internal.domain.tld service = 0 100 88 server1.internal.domain.tld.
_kerberos._tcp.internal.domain.tld service = 0 100 88 server2.internal.domain.tld.
...
_ldap._tcp.internal.domain.tld     service = 0 100 389 server1.internal.domain.tld.
_ldap._tcp.internal.domain.tld     service = 0 100 389 server2.internal.domain.tld.
...
Name:   server1.internal.domain.tld
Address: 192.168.1.1
NTP configuration
In an Active Directory domain, more specifically for Kerberos ticketing, it is imperative that time is synchronized with all other hosts on the network. A margin of error no more than five minutes is required. For the example domain configuration, an appropriate
/etc/ntp.conf
file should have the following contents (be sure to replace
server1
,
server2
, and
internal.domain.tld
with appropriate values for your network):
/etc/ntp.conf
# Use your domain's NTP servers 
server
server1
.
internal.domain.tld
server
server2
.
internal.domain.tld
# Restrictions
restrict default kod limited nomodify nopeer noquery notrap
restrict 127.0.0.1
restrict ::1

# Location of drift file
driftfile /var/lib/ntp/ntpd.drift
Enable and start the
ntpd.service
unit.
Kerberos configuration
The Samba documentation recommends a minimal Kerberos configuration, with just enough information in the
[libdefaults]
section to hand off the work of discovering domain details to DNS. Unfortunately, this does not work well in practice. Continuing with the example domain configuration, modify the
/etc/krb5.conf
file with the following contents (be sure to replace instances of
INTERNAL
,
internal.domain.tld
,
SERVER1
, and
INTERNAL.DOMAIN.TLD
with appropriate values for your network):
/etc/krb5.conf
[libdefaults]
   default_realm =
INTERNAL.DOMAIN.TLD
dns_lookup_realm = false
   dns_lookup_kdc = true

[realms]
INTERNAL.DOMAIN.TLD
= {
      kdc =
SERVER1
.
INTERNAL.DOMAIN.TLD
default_domain =
INTERNAL.DOMAIN.TLD
admin_server =
SERVER1
.
INTERNAL.DOMAIN.TLD
}
INTERNAL
= {
      kdc =
SERVER1
.
INTERNAL.DOMAIN.TLD
default_domain =
INTERNAL.DOMAIN.TLD
admin_server =
SERVER1
.
INTERNAL.DOMAIN.TLD
}

[domain_realm]
    .
internal.domain.tld
=
INTERNAL.DOMAIN.TLD
[appdefaults]
    pam = {
        ticket_lifetime = 1d
        renew_lifetime = 1d
        forwardable = true
        proxiable = false
        minimum_uid = 1
    }
Samba configuration
Base Samba configuration file
A default installation of
samba
does not ship with an example
/etc/samba/smb.conf
file. For our example domain configuration, use the following base settings (replace instances of
INTERNAL
and
INTERNAL.DOMAIN.TLD
with appropriate values for your network):
/etc/samba/smb.conf
[global]
   workgroup =
INTERNAL
security = ADS
   realm =
INTERNAL.DOMAIN.TLD
winbind refresh tickets = Yes
   vfs objects = acl_xattr
   map acl inherit = Yes
   store dos attributes = Yes

   # Allow a single, unified keytab to store obtained Kerberos tickets
   dedicated keytab file = /etc/krb5.keytab
   kerberos method = secrets and keytab

   # Do not require that login usernames include the default domain
   winbind use default domain = yes
If you do not wish to share local printers configured in
cups
, then add the following to the [Global] section of the
/etc/samba/smb.conf
file:
/etc/samba/smb.conf
[Global]
...
   load printers = no
   printing = bsd
   printcap name = /dev/null
   disable spoolss = yes
...
The remainder of the configuration depends on whether your domain supports RFC2307 Unix/NFS Attributes. Consult with your domain administrator if unsure.
Adding the idmap configuration for domains with RFC2307 extensions
Be certain that the values below do not overlap with system values, and that all users have at least the
uidNubmer
attribute, and that those users'
PrimaryGroup
has a
gid
attribute. Append to the following to the [Global] section of the
/etc/samba/smb.conf
file (replace
INTERNAL
with the NetBIOS domain name):
/etc/samba/smb.conf
[Global]
...

   # UID/GID mapping for local users
   idmap config * : backend = tdb
   idmap config * : range = 3000-7999

   # UID/GID mapping for domain users
   idmap config
INTERNAL
: backend = ad
   idmap config
INTERNAL
: schema_mode = rfc2307
   idmap config
INTERNAL
: range = 10000-999999
   idmap config
INTERNAL
: unix_nss_info = yes

   # Template settings for users without ''unixHomeDir'' and ''loginShell'' attributes 
   template shell = /bin/bash
   template homedir = /home/%U

   # Allow offline/cached credentials and ticket refresh
   winbind offline logon = yes
   winbind refresh tickets = yes
...
Additionally, if user accounts in AD have a
gidNumber
attribute, you can use it instead of the RID for the user's
Primary Group
by appending the following setting (again in the [Global] section):
/etc/samba/smb.conf
[Global]
...
   idmap config
INTERNAL
:unix_primary_group = yes
...
Adding the idmap configuration for domains without RFC2307 extensions
If your administrator has not extended the AD schema to include the RFC2307 attributes, use the following idmap configuration in the [Global] section of the
/etc/samba/smb.conf
file (replace
INTERNAL
with the NetBIOS domain name):
/etc/samba/smb.conf
[Global]
...
   # UID/GID mapping for local users
   idmap config * : backend = tdb
   idmap config * : range = 3000-7999

   # UID/GID mapping for domain users
   idmap config
INTERNAL
: backend = rid
   idmap config
INTERNAL
: range = 10000-999999

   # Template settings for users
   template shell = /bin/bash
   template homedir = /home/%U

   # Allow offline/cached credentials and ticket refresh
   winbind offline logon = yes
   winbind refresh tickets = yes
...
Joining the domain
To join the AD domain, simply issue the following command (be sure to replace
Administrator
with a user that has privileges to join the AD domain).
# net ads join -U Administrator
Start the individual Samba services
Enable and start the
smb.service
,
nmb.service
, and
winbind.service
services.
Configure NSS
Modify the
/etc/nsswitch.conf
file to allow Samba to map names to uid and gid:
/etc/nsswitch.conf
...
passwd: files winbind mymachines systemd
group: files winbind mymachines systemd
...
Testing NSS
Verify connectivity by listing the AD domain users and groups that system is aware of:
# wbinfo -u
# wbinfo -g
You should get a list of AD users followed by AD groups.
Configuring PAM authentication
Rather than configuring options directly in the
Linux-PAM
configuration files, set defaults for the
pam_winbind
module in
/etc/security/pam_winbind.conf
:
/etc/security/pam_winbind.conf
[Global]
   debug = no
   debug_state = no
   try_first_pass = yes
   krb5_auth = yes
   krb5_ccache_type = FILE:/run/user/%u/krb5cc
   cached_login = yes
   silent = no
   mkhomedir = yes
For most services, it will be sufficient to modify only the
/etc/pam.d/system-auth
file. Any configuration for programs that do not include this file will also need to be modified directly. Create a backup of the
/etc/pam.d/system-auth
file and use the following configuration:
/etc/pam.d/system-auth
#%PAM-1.0

auth       required                    pam_faillock.so      preauth
# Optionally use requisite above if you do not want to prompt for the password
# on locked accounts.
-auth      [success=3 default=ignore]  pam_systemd_home.so
auth       [success=2 default=ignore]  pam_winbind.so
auth       [success=1 default=bad]     pam_unix.so          try_first_pass nullok
auth       [default=die]               pam_faillock.so      authfail
auth       optional                    pam_permit.so
auth       required                    pam_env.so
auth       required                    pam_faillock.so      authsucc
# If you drop the above call to pam_faillock.so the lock will be done also
# on non-consecutive authentication failures.

-account   [success=2 default=ignore]  pam_systemd_home.so
account    [success=1 default=ignore]  pam_winbind.so
account    required                    pam_unix.so
account    optional                    pam_permit.so
account    required                    pam_time.so

-password  [success=2 default=ignore]  pam_systemd_home.so
password   [success=1 default=ignore]  pam_winbind.so
password   required                    pam_unix.so          try_first_pass nullok shadow sha512
password   optional                    pam_permit.so

-session   optional                    pam_systemd_home.so
session    required                    pam_mkhomedir.so skel=/etc/skel/ umask=0022
session    required                    pam_limits.so
session    required                    pam_winbind.so
session    required                    pam_unix.so
session    optional                    pam_permit.so
If you have other services that do not include the
/etc/pam.d/system-auth
file, modify the configuration to mirror all
pam_unix.so
entries for
pam_winbind.so
and  change all
required
to
sufficient
. A good example is the su configuration. Create a backup of the
/etc/pam.d/su
file and use the following in its place:
/etc/pam.d/su
#%PAM-1.0

auth      sufficient  pam_rootok.so
# Uncomment the following line to implicitly trust users in the "wheel" group.
#auth     required    pam_wheel.so   trust use_uid
# Uncomment the following line to require a user to be in the "wheel" group.
#auth     required    pam_wheel.so    use_uid
auth      sufficient  pam_winbind.so
auth      required    pam_unix.so
account   sufficient  pam_winbind.so
account   required    pam_unix.so
session   sufficient  pam_winbind.so
session   required    pam_unix.so
The above pam_winbind configuration will not use the default location of the Kerberos ticket (
KRB5CCNAME
), which is at
/tmp/krb5cc_
UID
. Instead, it stores the automatically refreshed Kerberos ticket to
/run/user/
UID
/krb5cc
. Append the following to your krb5.conf to let Kerberos know your new location:
/etc/krb5.conf
[libdefaults]
   ...
   default_ccache_name = /run/user/%{uid}/krb5cc
   ...
To test your changes, start a
new
console or ssh session (do not exit your existing session until you have tested thoroughly) 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 (see below).
Run
klist
to verify that you have received a kerberos ticket. You should see something similar to:
$ klist
Ticket cache: FILE:/run/user/20000/krb5cc
Default principal: administrator@INTERNAL.DOMAIN.TLD

Valid starting       Expires              Service principal
12/25/2020 03:35:21  12/25/2020 13:35:21  krbtgt/INTERNAL.DOMAIN.TLD@INTERNAL.DOMAIN.TLD
        renew until 12/26/2020 03:35:15
Finally, you should test login as both the root user and a local unprivileged user before logging out of your existing (working) session.
Old Wiki Article
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 their password and specifies whether they are 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.
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 is recommended you add the following parameters to your
smb.conf
file:
client signing = auto 
server signing = auto
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
pam-krb5
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:
/etc/resolv.conf
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.
Note
The DNS entry 127.0.0.53 in the /etc/resolv.conf file refers to the local DNS resolver provided by systemd-resolved. If you have configured your DNS Servers using Network manager this step is unnecessary and can cause issues if you modify the resolv.conf as suggested.
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
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.
/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
        kdc     =   PDC2.EXAMPLE.COM
        admin_server = PDC.EXAMPLE.COM
		admin_server = PDC2.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
Heimdal 1.3.1 deprecated DES encryption which is required for AD authentication before Windows Server 2008. You will probably have to add
allow_weak_crypto = true
to the
[libdefaults]
section.
Creating a Kerberos ticket
Note
The keys and commands are user specific: sudo will be root, so your non-elevated account can connect to a different AD user with a separate key.  If you only have one domain, it is not necessary to type @EXAMPLE.COM
Now you can query the AD domain controllers and request a kerberos ticket (
uppercase is necessary
):
kinit administrator@EXAMPLE.COM
Note
The suggested
smb.conf
, including
winbind use default domain = yes
cannot use
@EXAMPLE.COM
in the username.
kinit administrator
will bring in the
DOMAINNAME
from
smb.conf
.
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
pam_winbind.conf
If you get errors stating that /etc/security/pam_winbind.conf was not found, create the file and add the following:
/etc/security/pam_winbind.conf
[global]
  debug = no
  debug_state = no
  try_first_pass = yes
  krb5_auth = yes
  krb5_ccache_type = FILE
  cached_login = yes
  silent = no
  mkhomedir = yes
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.
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.
/etc/samba/smb.conf
[Global]
  netbios name = MYARCHLINUX
  workgroup = EXAMPLE
  realm = EXAMPLE.COM
  server string = %h Arch Linux Host
  security = ads
  encrypt passwords = yes
  password server = pdc.example.com
  client signing = auto
  server signing = auto

  idmap config * : backend = tdb
  idmap config * : range = 10000-20000

  winbind use default domain = Yes
  winbind enum users = Yes
  winbind enum groups = Yes
  winbind nested groups = Yes
  winbind separator = +
  winbind refresh tickets = yes
  winbind offline logon = yes
  winbind cache time = 300

  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
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'
# net ads join -U Administrator
Administrator's password: xxx
Using short domain name -- EXAMPLE
Joined 'MYARCHLINUX' to realm 'EXAMPLE.COM'
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
.
Note
In
samba
4.8.0-1, the Samba daemon units have been renamed from
smbd.service
,
nmbd.service
, and
winbindd.service
to
smb.service
,
nmb.service
, and
winbind.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.
/etc/nsswitch.conf
passwd:            files winbind
 shadow:            files winbind
 group:             files winbind 

 hosts:             files dns wins
Testing Winbind
Let us check if winbind is able to query the AD. The following command should return a list of AD users:
# wbinfo -u
administrator
guest
krbtgt
test.user
Note we created an Active Directory user called 'test.user' on the domain controller
We can do the same for AD groups:
# wbinfo -g
domain computers
domain controllers
schema admins
enterprise admins
cert publishers
domain admins
domain users
domain guests
group policy creator owners
ras and ias servers
allowed rodc password replication group
denied rodc password replication group
read-only domain controllers
enterprise read-only domain controllers
dnsadmins
dnsupdateproxy
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.
The following output shows what a stock Arch Linux install looks like:
# getent passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/bin/false
daemon:x:2:2:daemon:/sbin:/bin/false
mail:x:8:12:mail:/var/spool/mail:/bin/false
ftp:x:14:11:ftp:/srv/ftp:/bin/false
http:x:33:33:http:/srv/http:/bin/false
nobody:x:99:99:nobody:/:/bin/false
dbus:x:81:81:System message bus:/:/bin/false
ntp:x:87:87:Network Time Protocol:/var/empty:/bin/false
avahi:x:84:84:avahi:/:/bin/false
administrator:*:10001:10006:Administrator:/home/EXAMPLE/administrator:/bin/bash
guest:*:10002:10007:Guest:/home/EXAMPLE/guest:/bin/bash
krbtgt:*:10003:10006:krbtgt:/home/EXAMPLE/krbtgt:/bin/bash
test.user:*:10000:10006:Test User:/home/EXAMPLE/test.user:/bin/bash
And for groups:
# getent group
root:x:0:root
bin:x:1:root,bin,daemon
daemon:x:2:root,bin,daemon
sys:x:3:root,bin
adm:x:4:root,daemon
tty:x:5:
disk:x:6:root
lp:x:7:daemon
mem:x:8:
kmem:x:9:
wheel:x:10:root
ftp:x:11:
mail:x:12:
uucp:x:14:
log:x:19:root
utmp:x:20:
locate:x:21:
rfkill:x:24:
smmsp:x:25:
http:x:33:
games:x:50:
network:x:90:
video:x:91:
audio:x:92:
optical:x:93:
floppy:x:94:
storage:x:95:
scanner:x:96:
power:x:98:
nobody:x:99:
users:x:100:
dbus:x:81:
ntp:x:87:
avahi:x:84:
domain computers:x:10008:
domain controllers:x:10009:
schema admins:x:10010:administrator
enterprise admins:x:10011:administrator
cert publishers:x:10012:
domain admins:x:10013:test.user,administrator
domain users:x:10006:
domain guests:x:10007:
group policy creator owners:x:10014:administrator
ras and ias servers:x:10015:
allowed rodc password replication group:x:10016:
denied rodc password replication group:x:10017:krbtgt
read-only domain controllers:x:10018:
enterprise read-only domain controllers:x:10019:
dnsadmins:x:10020:
dnsupdateproxy:x:10021:
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 -U administrator%password | less
objectClass: top
objectClass: person
objectClass: organizationalPerson
objectClass: user
objectClass: computer
cn: myarchlinux
distinguishedName: CN=myarchlinux,CN=Computers,DC=leafscale,DC=inc
instanceType: 4
whenCreated: 20120206043413.0Z
whenChanged: 20120206043414.0Z
uSNCreated: 16556
uSNChanged: 16563
name: myarchlinux
objectGUID: 2c24029c-8422-42b2-83b3-a255b9cb41b3
userAccountControl: 69632
badPwdCount: 0
codePage: 0
countryCode: 0
badPasswordTime: 0
lastLogoff: 0
lastLogon: 129729780312632000
localPolicyFlags: 0
pwdLastSet: 129729764538848000
primaryGroupID: 515
objectSid: S-1-5-21-719106045-3766251393-3909931865-1105
...<snip>...
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:
auth required pam_unix.so ...
Delete it, and replace with:
auth [success=1 default=ignore] pam_localuser.so
auth [success=2 default=die] pam_winbind.so
auth [success=1 default=die] pam_unix.so nullok
auth requisite pam_deny.so
"account" section
Find the line:
account required pam_unix.so
Keep it, and add this below:
account [success=1 default=ignore] pam_localuser.so
account required pam_winbind.so
"password" section
Find the line:
password required pam_unix.so ...
Delete it, and replace with:
password [success=1 default=ignore] pam_localuser.so
password [success=2 default=die] pam_winbind.so
password [success=1 default=die] pam_unix.so sha512 shadow
password requisite pam_deny.so
"session" section
Find the line:
session required pam_unix.so
Keep it, and add this line immediately above it:
session required pam_mkhomedir.so skel=/etc/skel/ umask=0022
Below the pam_unix line, add these:
session [success=1 default=ignore] pam_localuser.so
session required pam_winbind.so
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:
password required pam_unix.so sha512 shadow nullok
Delete it, and replace with:
password include system-auth
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)
.
test.user
EXAMPLE+test.user
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.
/etc/samba/smb.conf
[MyShare]
  comment = Example Share
  path = /srv/exports/myshare
  read only = no
  browseable = yes
  valid users = @NETWORK+"Domain Admins" NETWORK+test.user
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.
# net ads keytab create -U administrator
verify the content of your keytab by running:
# klist -k /etc/krb5.keytab
Keytab name: FILE:/etc/krb5.keytab
KVNO Principal
---- --------------------------------------------------------------------------
   4 host/myarchlinux.example.com@EXAMPLE.COM
   4 host/myarchlinux.example.com@EXAMPLE.COM
   4 host/myarchlinux.example.com@EXAMPLE.COM
   4 host/myarchlinux.example.com@EXAMPLE.COM
   4 host/myarchlinux.example.com@EXAMPLE.COM
   4 host/MYARCHLINUX@EXAMPLE.COM
   4 host/MYARCHLINUX@EXAMPLE.COM
   4 host/MYARCHLINUX@EXAMPLE.COM
   4 host/MYARCHLINUX@EXAMPLE.COM
   4 host/MYARCHLINUX@EXAMPLE.COM
   4 MYARCHLINUX$@EXAMPLE.COM
   4 MYARCHLINUX$@EXAMPLE.COM
   4 MYARCHLINUX$@EXAMPLE.COM
   4 MYARCHLINUX$@EXAMPLE.COM
   4 MYARCHLINUX$@EXAMPLE.COM
Enabling keytab authentication
Now you need to tell winbind to use the file by adding these lines to the /etc/samba/smb.conf:
kerberos method = secrets and keytab
 dedicated keytab file = /etc/krb5.keytab
It should look something like this:
/etc/samba/smb.conf
[Global]
  netbios name = MYARCHLINUX
  workgroup = EXAMPLE
  realm = EXAMPLE.COM
  server string = %h Arch Linux Host
  security = ads
  encrypt passwords = yes
  password server = pdc.example.com
  kerberos method = secrets and keytab
  dedicated keytab file = /etc/krb5.keytab

  idmap config * : backend = tdb
  idmap config * : range = 10000-20000

  winbind use default domain = Yes
  winbind enum users = Yes
  winbind enum groups = Yes
  winbind nested groups = Yes
  winbind separator = +
  winbind refresh tickets = yes

  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
Restart
the
winbindd.service
Check if everything works by getting a machine ticket for your system by running
# kinit MYARCHLINUX$ -kt /etc/krb5.keytab
This should not give you any feedback but running 'klist' should show you sth like:
# klist
Ticket cache: FILE:/tmp/krb5cc_0
 Default principal: MYARCHLINUX$@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
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
Add these options to the
sshd_config
and
restart
sshd.service
after making the changes.
/etc/ssh/sshd_config
# Change to no to disable s/key passwords
ChallengeResponseAuthentication no

# Kerberos options
KerberosAuthentication yes
#KerberosOrLocalPasswd yes
KerberosTicketCleanup yes
KerberosGetAFSToken yes

# GSSAPI options
GSSAPIAuthentication yes
GSSAPICleanupCredentials yes
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 configuration file:
/etc/krb5.conf
forwardable     =       true
Secondly we need to add the following options to the user-specific SSH client configuration file to tell
ssh(1)
to use these options - alternatively they can be invoked using the
-o
options directly.
~/.ssh/config
GSSAPIAuthentication yes
GSSAPIDelegateCredentials yes
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
$ ssh
myarchlinux.example.com
you should get connected without needing to enter your password.
if you have key authentication additionally activated then you should perform
$ ssh -v
myarchlinux.example.com
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:
ktutil
addent -password -p ''username@EXAMPLE.COM'' -k 1 -e RC4-HMAC
- enter password for username -
wkt username.keytab
q
Now test the file by invoking:
$ kinit
username@EXAMPLE.COM
-kt username.keytab
It should not prompt 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 e.g your
shell configuration file
- 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.
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 ...
See also
Wikipedia - Active Directory
Wikipedia - Samba
Wikipedia - Kerberos
Samba - Documentation
Directory on Samba Wiki
Samba Wiki - Samba, Active Directory & LDAP
smb.conf(5)
Using SSSD
sssd
can be used instead of Samba to integrate with AD. See
SSSD documentation
.
Commercial solutions
Centrify
Likewise
OpenSource version
PowerBroker Identity Services Open
: formerly Likewise acquired by BeyondTrust
Centrify Express for Linux