Set Up Telnet Server
In this step, we will set up a Telnet server on the LabEx VM. Telnet is a network protocol used to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection. While Telnet is generally considered insecure due to its lack of encryption, it can be useful for testing and demonstration purposes in a controlled environment like our LabEx VM.
Since the LabEx VM uses Docker containers, we cannot directly use systemctl to manage services. Instead, we'll use xinetd to manage the Telnet service. xinetd (extended Internet daemon) is a super-server daemon that listens for incoming network connections and starts the appropriate service.
First, let's install the telnetd and xinetd packages. Open your terminal in the LabEx VM and execute the following command:
sudo apt update
sudo apt install telnetd xinetd -y
This command updates the package lists and installs the telnetd (Telnet server daemon) and xinetd packages. The -y flag automatically answers "yes" to any prompts during the installation.
Next, we need to configure xinetd to manage the Telnet service. Create a configuration file for Telnet in the /etc/xinetd.d/ directory. Use nano to create and edit the file:
sudo nano /etc/xinetd.d/telnet
Paste the following configuration into the nano editor:
service telnet
{
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/sbin/in.telnetd
log_on_failure += USERID
disable = no
}
This configuration tells xinetd to listen for Telnet connections, run the /usr/sbin/in.telnetd server as root, and log connection failures. disable = no ensures that the service is enabled.
Press Ctrl+X, then Y, then Enter to save the file and exit nano.
Now, restart the xinetd service to apply the changes. Since we cannot use systemctl, we will use a workaround by sending a HUP signal to the xinetd process. First, find the process ID of xinetd:
ps -ef | grep xinetd
You should see output similar to:
root 1234 1 0 10:00 ? 00:00:00 /usr/sbin/xinetd -stayalive -pidfile /run/xinetd.pid
labex 5678 5600 0 10:01 pts/0 00:00:00 grep --color=auto xinetd
Note the process ID of xinetd (in this example, it's 1234). Replace 1234 with the actual process ID from your output in the following command:
sudo kill -HUP 1234
This command sends a HUP signal to the xinetd process, causing it to reload its configuration.
Finally, let's verify that the Telnet server is running. You can try to connect to it from the same machine using the telnet command. Since telnet client might not be installed by default, we will use netcat to test the connection.
nc localhost 23
If the Telnet server is running, you should see a blank screen or a Telnet prompt. You can then close the connection by typing Ctrl+] followed by quit. If you get "Connection refused", double-check the steps above.
