Integrate Linux & Active Directory using Kerberos, WinBind, Samba

Integrate Linux & Active Directory using Kerberos, WinBind, Samba

We can integrate Linux & Active Directory using Kerberos, Winbind, Samba. Prerequisites to join an Ubuntu Server to Windows Active Directory,

  1. Your Ubuntu server should be able to reach AD server.
  2. Active Directory Domain administrator account or an account in Active Directory’s ‘Domain Admins’ group or an account, that has sufficient privilege to join your Ubuntu server to Active Directory domain.

Configure Hosts

The first step of Active Directory join is to edit the /etc/hosts file. Set your machine’s IP address and hostname in /etc/hosts file.

vi /etc/hosts

In the hosts file, please enter the below values,

xx.xx.xx.xx mymachine.domain.com

Example :-

vi /etc/hosts

In the hosts file, please enter the below values,

10.0.0.50 mymachine.domain.com

Configure Local Resolver

Next you need to setup the /etc/resolv.conf with your name server entries and search domain entry. Usually, the AD server IP itself will be the name server IPs, since DNS role may be installed in the same server.

vi /etc/resolv.conf

In the resolv.conf file, please enter the below values

nameserver xx.xx.xx.xx
nameserver xx.xx.xx.xx
search domain.com

Example :-

vi /etc/resolv.conf

Edit the resolv.conf file and please enter the below values

nameserver 10.0.0.2
nameserver 10.0.0.3
search domain.com

Install the Utilities

Install the required packages,

apt-get -y install winbind sssd sssd-tools samba-common krb5-user packagekit samba-common-bin samba-libs adcli ntp

During the Kerberos installation, you will see a pink screen. Just enter your full domain name in CAPITAL LETTERS,

Eg : DOMAIN.COM

select OK by pressing TAB

You may keep it as BLANK and press OK, if you wish to configure Kerberos later.

Configure NTP Settings

The date and time of your Ubuntu server\host must synchronize with Active Directory server. Add your active directory’s ntp hostname in the /etc/ntp.conf file,

vi /etc/ntp.conf
server ntphost1.domain.com
server ntphost2.domain.com

You can also keep it as Ubuntu’s NTP servers, provided your active directory server’s time and Ubuntu NTP server time are in sync.

vi /etc/ntp.conf

In that case, add the below values, instead of above values,

server 0.ubuntu.pool.ntp.org
server 1.ubuntu.pool.ntp.org
server 2.ubuntu.pool.ntp.org
server 3.ubuntu.pool.ntp.org

Now sync the Ubuntu host machine’s date and time with NTP server and then start the NTP service,

If you are using your Active Directory’s NTP service, then execute the below commands,

ntpdate ntphost1.domain.com
ntpdate ntphost2.domain.com
systemctl enable ntp
systemctl start ntp

or

/etc/init.d/ntp restart

or

/etc/rc.d/init.d/ntp restart

Configure Kerberos Settings

Create a file named krb5.conf,

vi /etc/krb5.conf

Enter the below values in the kerberos config file,

[libdefaults]
ticket_lifetime = 600
default_realm = DOMAIN
default_tkt_enctypes = des3-hmac-sha1 des-cbc-crc
default_tgs_enctypes = des3-hmac-sha1 des-cbc-crc
[realms]
DOMAIN = {
kdc = ip of you ads server
default_domain = DOMAIN
}
[domain_realm]
.domain = DOMAIN
domain = DOMAIN
[kdc]
profile = /etc/krb5kdc/kdc.conf
[logging]
kdc = FILE:/var/log/krb5kdc.log
admin_server = FILE:/var/log/kadmin.log
default = FILE:/var/log/krb5lib.logog

Now, try to get a valid Kerberos ticket for your active directory administrator account,

kinit administrator@DOMAIN.COM

Password for administrator@DOMAIN.COM: <enter password>

klist

Ticket cache: FILE:/tmp/krb5cc_0
Default principal: administrator@DOMAIN.COM
Valid starting Expires Service principal
02/11/2017 21:22:27 03/11/2017 07:22:27 krbtgt/DOMAIN.COM@DOMAIN.COM
renew until 02/11/2017 21:22:27

Configure NSSwitch

To configure the NSSwitch configuration, please edit the file /etc/nsswitch.conf

vi /etc/nsswitch.conf

Now enter the below values into your configuration file.

passwd: compat winbind
shadow: compat
group: compat winbind

Configure SAMBA Service

To configure the SAMBA service in your Ubuntu box, edit the samba configuration file /etc/samba/smb.conf

To edit the file, execute the command,

vi /etc/samba/smb.conf

Replace the DOMAIN with your domain name(without .com) and DOMAIN.COM with your complete domain name.

[global]
workgroup = DOMAIN
password server = hostname of your domain controller server
wins server = IP of wins server
realm = DOMAIN
security = ads
idmap uid = 16777216-33554431
idmap gid = 16777216-33554431
template shell = /bin/bash
winbind use default domain = false
winbind offline logon = false
winbind separator = + <<very important, as the default \ character does strange things in unix/linux.
allow trusted domains = Yes <<if you have them

Restart the Samba & Winbind

To restart the Samba and Winbind service, you may execute the below commands,

service smb restart
service winbind restart

or

/etc/init.d/smb restart
/etc/init.d/winbind restart

or

/etc/rc.d/init.d/smb restart
/etc/rc.d/init.d/winbind restart

Verify krb5.keytab

To list the content of /etc/krb5.keytab file, please execute the below command,

klist -kt

To show the available kerberos tickets, please execute the command,

klist -c /var/lib/sss/db/ccache_DOMAIN.COM

SUDOER Configuration

To enable a particular AD group to have admin privilege in the Ubuntu box, you need to edit the sudoer configuration. The sudo file is located at /etc/sudoers. The members of AD groups added in sudoers can perform sudo.

To edit the sudoers, please execute,

vi /etc/sudoers
# Members of the admin group may gain root privileges
#%admin ALL=(ALL) ALL
%admin ALL=(ALL) NOPASSWD:ALL
# Allow members of group sudo to execute any command
%sudo ALL=(ALL:ALL) NOPASSWD:ALL
## AD Domain Groups and Users
#Adding Domain Admins and it_support as admins
%domain\ admins ALL=(ALL) NOPASSWD:ALL
%it_support ALL=(ALL) NOPASSWD:ALL
#Adding user george as admin
george ALL=(ALL) NOPASSWD:ALL

Configure LightDM

To configure the lightDM, create the lightDM configuration file “/etc/lightdm/lightdm.conf“.

vi /etc/lightdm/lightdm.conf
[SeatDefaults]
allow-guest=false
greeter-hide-users=true
greeter-show-manual-login=true

Once the file is saved, restart the lightDM service by executing the below command,

service lightdm restart

Join the Ubuntu Host to Active Directory Domain

To join the Linux Host to Active Directory Domain, please execute the below command,

net ads join -U DOMAIN+username%password

Verify the AD connectivity

To verify the active directory connectivity, please execute the below commands.

To test the AD join, please execute the below command,

net ads testjoin

If the result is ‘Join is OK‘ , then test the winbind. To test the winbind service, please execute the below commands.

To list the AD users

wbinfo -u <ad user name>

To List the AD groups,

wbinfo -g <ad group name>

If it is displaying your AD group and Username details, then it means,your linux box is successfully integrated into the AD domain.

getent passwd
getent group
id <ad user="" name="">

Now try a server reboot. Also try to access using the server via SSH from an another host and perform sudo.

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