configure telnet server, 텔넷 서버 설정하기

9월 22, 2024

Configuring a Telnet server on a Linux system involves installing the Telnet server package, enabling the Telnet service, and configuring access. Here are the step-by-step instructions for setting up a Telnet server.

1. Installing Telnet Server

For Ubuntu/Debian-based Systems:

Install telnetd (Telnet daemon):

sudo apt update
sudo apt install telnetd

Install the xinetd service manager (if it's not already installed):
```
sudo apt install xinetd
```

For CentOS/RHEL-based Systems:

Install the telnet-server package:
```
sudo yum install telnet-server
```
Install the xinetd service manager:
```
sudo yum install xinetd
```

For Fedora:

Install the telnet-server package:
```
sudo dnf install telnet-server
```
Install xinetd:
```
sudo dnf install xinetd
```

2. Configuring Telnet

Once Telnet and xinetd are installed, you need to configure xinetd to manage the Telnet service.

Configure the Telnet service in xinetd: Edit or create the configuration file /etc/xinetd.d/telnet using a text editor like nano:
```
sudo nano /etc/xinetd.d/telnet
```

Add or modify the following configuration:

service telnet
{
    flags           = REUSE
    socket_type     = stream
    wait            = no
    user            = root
    server          = /usr/sbin/in.telnetd
    log_on_failure  += USERID
    disable         = no
}

Save and close the file.

3. Enable and Start the Telnet Service

For Systemd (Most modern Linux distributions like Ubuntu 16.04+ and CentOS 7+):

Enable and start xinetd:

sudo systemctl enable xinetd
sudo systemctl start xinetd

Verify that the Telnet service is running:
```
sudo systemctl status xinetd
```

For older init systems:

On older systems (pre-Systemd), use the following:

sudo service xinetd start
sudo chkconfig xinetd on

4. Opening Telnet Port (Optional)

By default, Telnet uses port 23. If you have a firewall enabled (like ufw or firewalld), you need to open this port.

For UFW (Ubuntu/Debian):

sudo ufw allow 23/tcp
sudo ufw reload

For Firewalld (CentOS/RHEL/Fedora):

sudo firewall-cmd --permanent --add-port=23/tcp
sudo firewall-cmd --reload

5. Verify Telnet Server

To check if the Telnet server is functioning correctly:

On the same machine:
```
telnet localhost
```
From another machine:
```
telnet <Telnet-server-IP>
```

6. Security Considerations

Telnet is an insecure protocol because it transmits data, including passwords, in plaintext. It's advisable to use Telnet only in trusted environments. For secure remote connections, it's better to use SSH (Secure Shell).

If you still need to use Telnet, consider using a VPN or other secure tunneling methods to encrypt the Telnet session.

IT