# NTP Server

Setting up an NTP (Network Time Protocol) server on an Ubuntu machine is a straightforward process. You can use **`chrony`** or **`ntpd`** (Network Time Protocol Daemon) to accomplish this task. Here's how to set up an NTP server using **`chrony`**, which is the preferred tool in modern versions of Ubuntu.

#### Steps to Set Up an NTP Server on Ubuntu (using `chrony`):

1. **Update your system:**

   Before installing new packages, it’s always a good idea to update your system.

   ```bash
   sudo apt update
   sudo apt upgrade
   ```
2. **Install `chrony`:**

   If it's not already installed, you can install `chrony` by running:

   ```bash
   sudo apt install chrony
   ```
3. **Configure `chrony` as an NTP server:**

   Now you need to configure `chrony` to act as an NTP server.

   * Open the configuration file with a text editor, for example:

     ```bash
     sudo nano /etc/chrony/chrony.conf
     ```
   * Find the line that begins with `server` (it’s usually a line like `server 0.centos.pool.ntp.org iburst`) and add the NTP servers you want to use. You can use public NTP servers like `pool.ntp.org`, or configure your own servers.
   * To configure `chrony` as an NTP server, you need to allow incoming NTP requests. Scroll to the bottom of the configuration file and add the following line:

     ```bash
     allow 192.168.0.0/16  # Allow NTP access from this subnet
     ```

     You can replace `192.168.0.0/16` with the IP address range of the clients that should be able to sync their time with this server.
4. **Restart the `chrony` service:**

   After making changes to the configuration file, restart the `chrony` service to apply the changes.

   ```bash
   sudo systemctl restart chrony
   ```
5. **Enable `chrony` to start on boot:**

   To ensure that `chrony` starts automatically when the system reboots, use the following command:

   ```bash
   sudo systemctl enable chrony
   ```
6. **Verify the NTP server status:**

   You can check if the `chrony` service is running properly by typing:

   ```bash
   sudo systemctl status chrony
   ```

   Or you can check if the server is syncing correctly:

   ```bash
   chronyc tracking
   ```
7. **Allow NTP through the firewall (if applicable):**

   If you're using `ufw` (Uncomplicated Firewall), you need to allow NTP traffic (UDP port 123):

   ```bash
   sudo ufw allow 123/udp
   ```
8. **Test the NTP server:**

   To test if the NTP server is working, you can try syncing time from a client machine. On the client machine, you can use the following command:

   ```bash
   sudo chronyc -a makestep
   ```

   You can also configure the client to use your server for NTP by editing the `chrony.conf` file on the client:

   ```bash
   sudo nano /etc/chrony/chrony.conf
   ```

   Add the NTP server's IP address (the one you just set up) under the `server` directive:

   ```bash
   server <your_server_ip> iburst
   ```

   Then restart the client service:

   ```bash
   sudo systemctl restart chrony
   ```