# Manually join an Amazon EC2 Linux instance to your Simple AD Active Directory
<a name="simple_ad_join_linux_instance"></a>

In addition to Amazon EC2 Windows instances, you can also join certain Amazon EC2 Linux instances to your Simple AD Active Directory. The following Linux instance distributions and versions are supported:
+ Amazon Linux AMI 2018.03.0
+ Amazon Linux 2 (64-bit x86)
+ Amazon Linux 2023 AMI
+ Red Hat Enterprise Linux 8 (HVM) (64-bit x86)
+ Ubuntu Server 18.04 LTS & Ubuntu Server 16.04 LTS
+ CentOS 7 x86-64
+ SUSE Linux Enterprise Server 15 SP1

**Note**  
Other Linux distributions and versions may work but have not been tested.

## Prerequisites
<a name="simple_ad_join_linux_prereq"></a>

Before you can join either an Amazon Linux, CentOS, Red Hat, or Ubuntu instance to your directory, the instance must first be launched as specified in [Seamlessly join an Amazon EC2 Linux instance to your Simple AD Active Directory](simple_ad_seamlessly_join_linux_instance.md).

**Important**  
Some of the following procedures, if not performed correctly, can render your instance unreachable or unusable. Therefore, we strongly suggest you make a backup or take a snapshot of your instance before performing these procedures.

**To join a Linux instance to your directory**  
Follow the steps for your specific Linux instance using one of the following tabs:

------
#### [ Amazon Linux ]<a name="amazonlinux"></a>

1. Connect to the instance using any SSH client.

1. Configure the Linux instance to use the DNS server IP addresses of the Directory Service-provided DNS servers. You can do this either by setting it up in the DHCP Options set attached to the VPC or by setting it manually on the instance. If you want to set it manually, see [How do I assign a static DNS server to a private Amazon EC2 instance](https://aws.amazon.com/premiumsupport/knowledge-center/ec2-static-dns-ubuntu-debian/) in the AWS Knowledge Center for guidance on setting the persistent DNS server for your particular Linux distribution and version.

1. Make sure your Amazon Linux - 64bit instance is up to date.

   ```
   sudo yum -y update
   ```

1. Install the required Amazon Linux packages on your Linux instance.
**Note**  
Some of these packages may already be installed.   
As you install the packages, you might be presented with several pop-up configuration screens. You can generally leave the fields in these screens blank.  
Amazon Linux  

   ```
   sudo yum install samba-common-tools realmd oddjob oddjob-mkhomedir sssd adcli krb5-workstation
   ```
**Note**  
For help with determining the Amazon Linux version you are using, see [Identifying Amazon Linux images](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/amazon-linux-ami-basics.html#amazon-linux-image-id) in the *Amazon EC2 User Guide for Linux Instances*.

1. Join the instance to the directory with the following command. 

   ```
   sudo realm join -U join_account@EXAMPLE.COM example.com --verbose
   ```  
*join\$1account@EXAMPLE.COM*  
An account in the *example.com* domain that has domain join privileges. Enter the password for the account when prompted. For more information about delegating these privileges, see [Delegating directory join privileges for AWS Managed Microsoft AD](directory_join_privileges.md).  
*example.com*  
The fully qualified DNS name of your directory.

   ```
   ...
    * Successfully enrolled machine in realm
   ```

1. Set the SSH service to allow password authentication.

   1. Open the `/etc/ssh/sshd_config` file in a text editor.

      ```
      sudo vi /etc/ssh/sshd_config
      ```

   1. Set the `PasswordAuthentication` setting to `yes`.

      ```
      PasswordAuthentication yes
      ```

   1. Restart the SSH service.

      ```
      sudo systemctl restart sshd.service
      ```

      Alternatively:

      ```
      sudo service sshd restart
      ```

1. After the instance has restarted, connect to it with any SSH client and add the domain admins group to the sudoers list by performing the following steps:

   1. Open the `sudoers` file with the following command:

      ```
      sudo visudo
      ```

   1. Add the following to the bottom of the `sudoers` file and save it.

      ```
      ## Add the "Domain Admins" group from the example.com domain.
      %Domain\ Admins@example.com ALL=(ALL:ALL) ALL
      ```

      (The above example uses "\$1<space>" to create the Linux space character.)

------
#### [ CentOS ]<a name="centos"></a>

1. Connect to the instance using any SSH client.

1. Configure the Linux instance to use the DNS server IP addresses of the Directory Service-provided DNS servers. You can do this either by setting it up in the DHCP Options set attached to the VPC or by setting it manually on the instance. If you want to set it manually, see [How do I assign a static DNS server to a private Amazon EC2 instance](https://aws.amazon.com/premiumsupport/knowledge-center/ec2-static-dns-ubuntu-debian/) in the AWS Knowledge Center for guidance on setting the persistent DNS server for your particular Linux distribution and version.

1. Make sure your CentOS 7 instance is up to date.

   ```
   sudo yum -y update
   ```

1. Install the required CentOS 7 packages on your Linux instance.
**Note**  
Some of these packages may already be installed.   
As you install the packages, you might be presented with several pop-up configuration screens. You can generally leave the fields in these screens blank.

   ```
   sudo yum -y install sssd realmd krb5-workstation samba-common-tools
   ```

1. Join the instance to the directory with the following command. 

   ```
   sudo realm join -U join_account@example.com example.com --verbose
   ```  
*join\$1account@example.com*  
An account in the *example.com* domain that has domain join privileges. Enter the password for the account when prompted. For more information about delegating these privileges, see [Delegating directory join privileges for AWS Managed Microsoft AD](directory_join_privileges.md).  
*example.com*  
The fully qualified DNS name of your directory.

   ```
   ...
    * Successfully enrolled machine in realm
   ```

1. Set the SSH service to allow password authentication.

   1. Open the `/etc/ssh/sshd_config` file in a text editor.

      ```
      sudo vi /etc/ssh/sshd_config
      ```

   1. Set the `PasswordAuthentication` setting to `yes`.

      ```
      PasswordAuthentication yes
      ```

   1. Restart the SSH service.

      ```
      sudo systemctl restart sshd.service
      ```

      Alternatively:

      ```
      sudo service sshd restart
      ```

1. After the instance has restarted, connect to it with any SSH client and add the domain admins group to the sudoers list by performing the following steps:

   1. Open the `sudoers` file with the following command:

      ```
      sudo visudo
      ```

   1. Add the following to the bottom of the `sudoers` file and save it.

      ```
      ## Add the "Domain Admins" group from the example.com domain.
      %Domain\ Admins@example.com ALL=(ALL:ALL) ALL
      ```

      (The above example uses "\$1<space>" to create the Linux space character.)

------
#### [ Red hat ]<a name="redhat"></a>

1. Connect to the instance using any SSH client.

1. Configure the Linux instance to use the DNS server IP addresses of the Directory Service-provided DNS servers. You can do this either by setting it up in the DHCP Options set attached to the VPC or by setting it manually on the instance. If you want to set it manually, see [How do I assign a static DNS server to a private Amazon EC2 instance](https://aws.amazon.com/premiumsupport/knowledge-center/ec2-static-dns-ubuntu-debian/) in the AWS Knowledge Center for guidance on setting the persistent DNS server for your particular Linux distribution and version.

1. Make sure the Red Hat - 64bit instance is up to date.

   ```
   sudo yum -y update
   ```

1. Install the required Red Hat packages on your Linux instance.
**Note**  
Some of these packages may already be installed.   
As you install the packages, you might be presented with several pop-up configuration screens. You can generally leave the fields in these screens blank.

   ```
   sudo yum -y install sssd realmd krb5-workstation samba-common-tools
   ```

1. Join the instance to the directory with the following command. 

   ```
   sudo realm join -v -U join_account example.com --install=/
   ```  
*join\$1account*  
The **sAMAccountName** for an account in the *example.com* domain that has domain join privileges. Enter the password for the account when prompted. For more information about delegating these privileges, see [Delegating directory join privileges for AWS Managed Microsoft AD](directory_join_privileges.md).  
*example.com*  
The fully qualified DNS name of your directory.

   ```
   ...
    * Successfully enrolled machine in realm
   ```

1. Set the SSH service to allow password authentication.

   1. Open the `/etc/ssh/sshd_config` file in a text editor.

      ```
      sudo vi /etc/ssh/sshd_config
      ```

   1. Set the `PasswordAuthentication` setting to `yes`.

      ```
      PasswordAuthentication yes
      ```

   1. Restart the SSH service.

      ```
      sudo systemctl restart sshd.service
      ```

      Alternatively:

      ```
      sudo service sshd restart
      ```

1. After the instance has restarted, connect to it with any SSH client and add the domain admins group to the sudoers list by performing the following steps:

   1. Open the `sudoers` file with the following command:

      ```
      sudo visudo
      ```

   1. Add the following to the bottom of the `sudoers` file and save it.

      ```
      ## Add the "Domain Admins" group from the example.com domain.
      %Domain\ Admins@example.com ALL=(ALL:ALL) ALL
      ```

      (The above example uses "\$1<space>" to create the Linux space character.)

------
#### [ Ubuntu ]<a name="ubuntu"></a>

1. Connect to the instance using any SSH client.

1. Configure the Linux instance to use the DNS server IP addresses of the Directory Service-provided DNS servers. You can do this either by setting it up in the DHCP Options set attached to the VPC or by setting it manually on the instance. If you want to set it manually, see [How do I assign a static DNS server to a private Amazon EC2 instance](https://aws.amazon.com/premiumsupport/knowledge-center/ec2-static-dns-ubuntu-debian/) in the AWS Knowledge Center for guidance on setting the persistent DNS server for your particular Linux distribution and version.

1. Make sure your Ubuntu - 64bit instance is up to date.

   ```
   sudo apt-get update
   sudo apt-get -y upgrade
   ```

1. Install the required Ubuntu packages on your Linux instance.
**Note**  
Some of these packages may already be installed.   
As you install the packages, you might be presented with several pop-up configuration screens. You can generally leave the fields in these screens blank.

   ```
   sudo apt-get -y install sssd realmd krb5-user samba-common packagekit adcli
   ```

1. Disable Reverse DNS resolution and set the default realm to your domain's FQDN. Ubuntu Instances **must** be reverse-resolvable in DNS before the realm will work. Otherwise, you have to disable reverse DNS in /etc/krb5.conf as follows:

   ```
   sudo vi /etc/krb5.conf
   ```

   ```
   [libdefaults]
   default_realm = EXAMPLE.COM
   rdns = false
   ```

1. Join the instance to the directory with the following command. 

   ```
   sudo realm join -U join_account example.com --verbose
   ```  
*join\$1account@example.com*  
The **sAMAccountName** for an account in the *example.com* domain that has domain join privileges. Enter the password for the account when prompted. For more information about delegating these privileges, see [Delegating directory join privileges for AWS Managed Microsoft AD](directory_join_privileges.md).  
*example.com*  
The fully qualified DNS name of your directory.

   ```
   ...
    * Successfully enrolled machine in realm
   ```

1. Set the SSH service to allow password authentication.

   1. Open the `/etc/ssh/sshd_config` file in a text editor.

      ```
      sudo vi /etc/ssh/sshd_config
      ```

   1. Set the `PasswordAuthentication` setting to `yes`.

      ```
      PasswordAuthentication yes
      ```

   1. Restart the SSH service.

      ```
      sudo systemctl restart sshd.service
      ```

      Alternatively:

      ```
      sudo service sshd restart
      ```

1. After the instance has restarted, connect to it with any SSH client and add the domain admins group to the sudoers list by performing the following steps:

   1. Open the `sudoers` file with the following command:

      ```
      sudo visudo
      ```

   1. Add the following to the bottom of the `sudoers` file and save it.

      ```
      ## Add the "Domain Admins" group from the example.com domain.
      %Domain\ Admins@example.com ALL=(ALL:ALL) ALL
      ```

      (The above example uses "\$1<space>" to create the Linux space character.)

------

**Note**  
When using Simple AD, if you create a user account on a Linux instance with the option "Force user to change password at first login," that user will not be able to initially change their password using **kpasswd**. In order to change the password the first time, a domain administrator must update the user password using the Active Directory Management Tools.

## Manage accounts from a Linux instance
<a name="simple_ad_manage_accounts"></a>

To manage accounts in Simple AD from a Linux instance, you must update specific configuration files on your Linux instance as follows:

1. Set **krb5\$1use\$1kdcinfo** to **False** in the **/etc/sssd/sssd.conf** file. For example:

   ```
   [domain/example.com]
       krb5_use_kdcinfo = False
   ```

1. In order for the configuration to take affect you need to restart the sssd service:

   ```
   $ sudo systemctl restart sssd.service
   ```

   Alternatively, you could use:

   ```
   $ sudo service sssd start
   ```

1. If you will be managing users from a CentOS Linux instance, you must also edit the file **/etc/smb.conf** to include: 

   ```
   [global] 
     workgroup = EXAMPLE.COM
     realm = EXAMPLE.COM 
     netbios name = EXAMPLE
     security = ads
   ```

## Restricting account login access
<a name="simple_ad_linux_filter"></a>

Since all accounts are defined in Active Directory, by default, all the users in the directory can log in to the instance. You can allow only specific users to log in to the instance with **ad\$1access\$1filter** in **sssd.conf**. For example:

```
ad_access_filter = (memberOf=cn=admins,ou=Testou,dc=example,dc=com)
```

*memberOf*  
Indicates that users should only be allowed access to the instance if they are a member of a specific group.

*cn*  
The common name of the group that should have access. In this example, the group name is *admins*.

*ou*  
This is the organizational unit in which the above group is located. In this example, the OU is *Testou*.

*dc*  
This is the domain component of your domain. In this example, *example*.

*dc*  
This is an additional domain component. In this example, *com*.

You must manually add **ad\$1access\$1filter** to your **/etc/sssd/sssd.conf**.

Open the **/etc/sssd/sssd.conf** file in a text editor.

```
sudo vi /etc/sssd/sssd.conf
```

After you do this, your **sssd.conf** might look like this:

```
[sssd]
domains = example.com
config_file_version = 2
services = nss, pam

[domain/example.com]
ad_domain = example.com
krb5_realm = EXAMPLE.COM
realmd_tags = manages-system joined-with-samba
cache_credentials = True
id_provider = ad
krb5_store_password_if_offline = True
default_shell = /bin/bash
ldap_id_mapping = True
use_fully_qualified_names = True
fallback_homedir = /home/%u@%d
access_provider = ad
ad_access_filter = (memberOf=cn=admins,ou=Testou,dc=example,dc=com)
```

In order for the configuration to take effect, you need to restart the sssd service:

```
sudo systemctl restart sssd.service
```

Alternatively, you could use:

```
sudo service sssd restart
```

## ID Mapping
<a name="simple-ad-id-mapping"></a>

ID mapping can be performed by two methods to maintain a unified experience between UNIX/Linux User Identifier (UID) and Group Identifier (GID) and Windows and Active Directory Security Identifier (SID) identities. These methods are:

1. Centralized

1. Distributed

**Note**  
Centralized user identity mapping in Active Directory requires Portable Operating System Interface or POSIX.

**Centralized user identity mapping**  
Active Directory or another Lightweight Directory Access Protocol (LDAP) service provides UID and GID to the Linux users. In Active Directory, these identifiers are stored in the users' attributes if the POSIX extension is configured:
+ UID - The Linux username (String)
+ UID Number - The Linux User ID number (Integer)
+ GID Number - The Linux Group ID number (Integer)

To configure a Linux instance to use the UID and GID from Active Directory, set `ldap_id_mapping = False` in the sssd.conf file. Before setting this value, verify you have added a UID, UID number and GID number to the users and groups in Active Directory.

**Distributed user identity mapping**  
If Active Directory doesn't have the POSIX extension or if you choose not to centrally manage identity mapping, Linux can calculate the UID and GID values. Linux uses the user's unique Security Identifier (SID) to maintain consistency.

To configure distributed user ID mapping, set `ldap_id_mapping = True` in the sssd.conf file.

**Common issues**  
If you set `ldap_id_mapping = False`, sometimes starting the SSSD service will fail. The reason for this failure is due to changing UIDs not supported. We recommend you delete the SSSD cache whenever you change from ID mapping to POSIX attributes or from POSIX attributes to ID mapping. For further details about ID mapping and the ldap\$1id\$1mapping parameters, see the sssd-ldap(8) man page in the Linux command line.

## Connect to the Linux instance
<a name="simple_ad_linux_connect"></a>

When a user connects to the instance using an SSH client, they are prompted for their username. The user can enter the username in either the `username@example.com` or `EXAMPLE\username` format. The response will appear similar to the following, depending on which Linux distribution you are using:

**Amazon Linux, Red Hat Enterprise Linux, and CentOS Linux**

```
login as: johndoe@example.com
johndoe@example.com's password:
Last login: Thu Jun 25 16:26:28 2015 from XX.XX.XX.XX
```

**SUSE Linux**

```
SUSE Linux Enterprise Server 15 SP1 x86_64 (64-bit)

As "root" (sudo or sudo -i) use the:
  - zypper command for package management
  - yast command for configuration management

Management and Config: https://www.suse.com/suse-in-the-cloud-basics
Documentation: https://www.suse.com/documentation/sles-15/
Forum: https://forums.suse.com/forumdisplay.php?93-SUSE-Public-Cloud

Have a lot of fun...
```

**Ubuntu Linux**

```
login as: admin@example.com
admin@example.com@10.24.34.0's password:
Welcome to Ubuntu 18.04.4 LTS (GNU/Linux 4.15.0-1057-aws x86_64)

* Documentation:  https://help.ubuntu.com
* Management:     https://landscape.canonical.com
* Support:        https://ubuntu.com/advantage

  System information as of Sat Apr 18 22:03:35 UTC 2020

  System load:  0.01              Processes:           102
  Usage of /:   18.6% of 7.69GB   Users logged in:     2
  Memory usage: 16%               IP address for eth0: 10.24.34.1
  Swap usage:   0%
```