Authenticating Linux clients against MS Active Directory

Authenticating Linux clients against MS Active Directory

The page describes the necessary steps to enable Ubuntu 12.04 clients to authenticate users against AIT's Active Directory (AD) server. Groups and settings in DTU-Basen can be used on the clients, as well as, user home directories from dtu-storage.

The setup is heavily inspired by the following manual for RHEL systems: Linux-AD

Install Samba and Kerberos:

$ sudo apt-get install samba krb5-user winbind smbfs

Setup Kerberos (/etc/krb5.conf):

[libdefaults]
	default_realm = WIN.DTU.DK
	dns_lookup_realm = true
	dns_lookup_kdc = true
	ticket_lifetime = 24h
	renew_lifetime = 7d
	forwardable = true

[realms]
WIN.DTU.DK = {
	default_domain = win.dtu.dk
}

[domain_realm]
.win.dtu.dk = WIN.DTU.DK
win.dtu.dk = WIN.DTU.DK

Setup Samba (/etc/samba/smb.conf):

#======================= Global Settings =======================

[global]
   workgroup = WIN
   server string = kapok
   syslog = 0

   panic action = /usr/share/samba/panic-action %d

   security = ADS
   realm = WIN.DTU.DK
   netbios name = elek-aut-01

   idmap config * : backend = rid
   idmap config * : range = 5000-100000000
   idmap config * : base_rid = 0
   template shell = /bin/bash
   template homedir = /home/%D/%U
   winbind use default domain = true
   winbind offline logon = false
   winbind enum users = No
   winbind enum groups = No
   winbind nested groups = Yes
   allow trusted domains = No

Add the machine to the AD

Get a Kerberos ticket by issuing:

$ sudo kinit <campusnet-login>@WIN.DTU.DK

Add the PC to the AD domain by issuing:

$ sudo net ads join -U <campusnet-login>

The PC name needs to start with "elek-" (when dealing with DTU-Elektro machines). The name should be the same as "netbios name" in the Samba configuration file. Dual-boot Windows machines that already has an "elek-" name must be given a different name to avoid conflicting AD instances. (Even WinXP and Win7 can't share the same AD instance).

Add Winbind to the nsswitch configuration. (/etc/nsswitch.conf):

passwd:         nis compat winbind
group:          nis compat winbind
shadow:         nis compat winbind 

hosts:          files dns wins mdns4
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

netgroup:       nis

Check that

$ wbinfo -u

gives a list of all AD users. (This might take a while).

Automatic mounting of home directory

By installing "pam_mount" it is possible to automatically mount AD users home directory upon login. The package is installed by:

$ sudo apt-get install libpam-mount

A skeleton homedrive (mount point) can be created using pam_mkhomedir. This is done by adding session required pam_mkhomedir.so skel=/etc/skel umask=0077 to /etc/pam.d/common-session just before pam_mount. Listing of /etc/pam.d/common-session:

session	[default=1]			pam_permit.so
session	requisite			pam_deny.so

session	required			pam_permit.so

session	optional			pam_umask.so

session	required	pam_unix.so 
session	optional			pam_winbind.so 
session	required	pam_mkhomedir.so skel=/etc/skel umask=0077
session	optional	pam_mount.so 
session	optional			pam_ck_connector.so nox11

A somewhat working pam_mount configuration is (/etc/security/pam_mount.conf.xml): <syntaxhighlight lang="xml">

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE pam_mount SYSTEM "pam_mount.conf.xml.dtd">

<pam_mount>
 
<debug enable="0" />
 
<mntoptions deny="suid,dev" />
<mntoptions allow="*" />
<mntoptions deny="*" />
-->
<mntoptions require="nosuid,nodev" />

<logout wait="100000" hup="yes" term="yes" kill="no" />

<volume pgrp="domain users" server="dtu-storage.win.dtu.dk" path="" mountpoint="home/WIN" fstype="cifs" />

<cifsmount>mount -t cifs //%(SERVER)/%(USER) %(MNTPT)/%(USER) -o "username=%(USER),uid=%(USERUID),gid=%(USERGID),file_mode=0700,dir_mode=0700%(before=\",\" OPTIONS)"
</cifsmount> 

<umount>umount %(MNTPT)/%(USER)</umount>

<mkmountpoint enable="1" remove="false" />

</pam_mount>

There are problems with multiple mounts and mounts that hang upon logout.