# Ubuntu Host Preparation for Pi-hole (Port 53 Conflict Fix)

## 1. The Issue: Port 53 Conflict
By default, Ubuntu runs `systemd-resolved`, which acts as a local DNS stub listener on **Port 53**. Pi-hole also requires Port 53 to function as a DNS server. If `systemd-resolved` is not modified, the Pi-hole container will fail to start with an "address already in use" error.

## 2. The Fix: Steps to Release Port 53

### Step 1: Disable the DNS Stub Listener
1. Open the resolved configuration file:
```bash
sudo nano /etc/systemd/resolved.conf
```
2. Locate the line `#DNSStubListener=yes`.
3. Change it to:
```ini
DNSStubListener=no
```
4. Save and exit (`Ctrl+O`, `Enter`, `Ctrl+X`).

### Step 2: Fix Local DNS Resolution

Since the stub listener is disabled, the default `127.0.0.53` DNS entry will no longer work. Point the system to the upstream DNS file instead so the host maintains internet connectivity.

1. Remove the existing symlink:
```bash
sudo rm /etc/resolv.conf

```


2. Create a new symlink to the actual resolv file:
```bash
sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf

```

### Step 3: Reload and Restart Services

Apply the changes and reload the daemon to clear any configuration warnings.

```bash
sudo systemctl daemon-reload
sudo systemctl restart systemd-resolved

```

### Verification

Check if Port 53 is free (output should be empty or not show `systemd-resolved`):

```bash
sudo lsof -i :53
```