# Connecting Linux server to Active Directory

{% hint style="info" %}
This guide outlines the steps to connect a Linux server to an Active Directory (AD) domain. The process varies slightly between Ubuntu and CentOS distributions.
{% endhint %}

***

#### **1. Edit /etc/hosts File**

Edit the `/etc/hosts` file to add or update the Fully Qualified Domain Name (FQDN) for the host:

```bash
bashCopy code127.0.1.1       <hostname>.<Domain_Name>  <hostname>
```

You may also need to add the FQDN for the AD server:

```bash
bashCopy code<server_ip>       <Server_Name>.<Domain_Name>  <Server_Name>
```

Ensure the AD server is installed as a DNS server for proper connectivity. Check the current DNS settings with:

```bash
bashCopy codecat /etc/resolv.conf
```

***

#### **2. Configure DNS Settings**

**Ubuntu 18.04**

1. **Install resolvconf package**:

   ```bash
   bashCopy codesudo apt update
   sudo apt install resolvconf
   sudo systemctl enable resolvconf.service
   ```
2. **Edit the `/etc/resolvconf/resolv.conf.d/head` file** to add the line:

   ```bash
   bashCopy codenameserver  <server_ip>
   ```
3. **Start the resolvconf service**:

   ```bash
   bashCopy codesudo systemctl start resolvconf.service
   ```

**CentOS 7**

1. **Add the following lines to the network interface configuration** (replace `ifcfg-*` with your actual network interface):

   ```bash
   bashCopy codePEERDNS=no
   DNS1=<server_ip>
   ```
2. **Restart the NetworkManager**:

   ```bash
   bashCopy codesudo systemctl restart NetworkManager
   ```
3. **Check `/etc/resolv.conf` again**:

   ```bash
   bashCopy codecat /etc/resolv.conf
   ```
4. **(Optional) Install bind-utils**:

   ```bash
   bashCopy codesudo yum install bind-utils -y
   ```
5. **Verify domain resolution**:

   ```bash
   bashCopy codenslookup <Domain_Name>
   ```

***

#### **3. Install Necessary Packages**

**Ubuntu 18.04**

```bash
bashCopy codesudo apt install realmd samba-common-bin samba-libs sssd-tools krb5-user adcli
```

**CentOS 7**

```bash
bashCopy codesudo yum install sssd realmd oddjob oddjob-mkhomedir adcli samba-common samba-common-tools krb5-workstation openldap-clients policycoreutils-python -y
```

During the installation of Kerberos, confirm the domain and specify the server name.

***

#### **4. Discover the Domain**

Check if the domain is visible on the network:

```bash
bashCopy coderealm discover <Domain_Name>
```

***

#### **5. Join the Domain**

To join the machine to the domain, use:

```bash
bashCopy codesudo realm --verbose join <Domain_Name> -U <YourDomainAdmin> --install=/
```

If there are no errors, the server should now appear in the domain controller.

***

#### **6. Update ldap.conf for Self-Signed Certificates**

If the Active Directory server uses self-signed certificates, edit the `ldap.conf` file:

* **Ubuntu**: `/etc/ldap/ldap.conf`
* **CentOS**: `/etc/openldap/ldap.conf`

Add the following parameter at the end of the file:

```bash
bashCopy codeTLS_REQCERT never
```

***

#### **7. Installation Check**

To retrieve all users, execute the following command (you will need to enter a password):

```bash
bashCopy codeldapsearch -x -H "ldaps://<Domain_Name>" -D "<YourDomainAdmin>@<Domain_Name>" -W -b "dc=<dc>,dc=<dc>, ..." "objectCategory=person" name
```

For example, if your domain is `hideez.example.com` and your administrator is named "administrator", the command would look like this:

```bash
bashCopy codeldapsearch -x -H "ldaps://hideez.example.com" -W -D "administrator@hideez.example.com" -b "dc=hideez,dc=example,dc=com" "objectCategory=person" name
```

#### **8. Troubleshooting**

If you encounter an error, add the `-d1` option to the command to get detailed error information.

```bash
bashCopy codeldapsearch -x -H "ldaps://hideez.example.com" -W -D "administrator@hideez.example.com" -b "dc=hideez,dc=example,dc=com" "objectCategory=person" name -d1
```

***

{% hint style="info" %}
By following these steps, you should successfully connect your Linux server to an Active Directory environment.
{% endhint %}


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