How to access my computer's terminal in the university dorm from another computer?

Question

I have used ssh to access remote computers/servers where they provided me a username, a password, and an IP address (like xxx:xxx:xx.xx). What I need to do is:

ssh [email protected]

and then it will ask for the password. After entering the password, it gives me the terminal control where I can control everything from the terminal of this remote server.

I want something exactly like this but to access my own computer. I run my ubuntu pc 24/7. I want to host my pc so that from another pc/mobile terminal I can access this. How to setup my pc as a server?

I saw several answers about openssh-server. I installed it and then did the following:

sudo systemctl enable ssh
sudo ufw allow ssh
sudo systemctl start ssh

But I cannot understand how I can access my computer. What is the IP address from my computer? I am looking for a step-by-step guide or some reference on how to enable such thing and how I can access my computer terminal remotely.

Here are my PC details:

I am using Ubuntu Desktop 20.04.6 LTS (Focal Fossa).

I downloaded the ubuntu-20.04.6-desktop-amd64.iso from releases.ubuntu.com.

I am not sure about my IP address. When I checked it through https://whatismyipaddress.com/, it shows that I have a Likely static IP. However, when I connect to a different router, my IP address changed. So, probably it is dynamic.

Addition: I have followed the steps in this answer provided by Aleff below. However, since the router I am using is a public router (university dorm router), I don't have access to its configuration page. So, I cannot enable port forwarding. I am looking for a workaround in this step.

Answer 1

If you don't have access to the router to do port forwarding, BUT you do have a ssh access to some server that is outside your local network and is accessible from the Internet, you can use that server as a "middleman" to access your PC.

First, you need to establish a ssh tunnel between your PC and that server, by using on your PC a command like:

ssh -R portnumber:localhost:22 [email protected]

where username is your username at external.server and portnumber is any unused port number on that server that you will choose (for example, 9922). "localhost" is literally the word localhost.

You should leave this connection active permanently. You have to ensure somehow that this connection is kept up all the time and does not disconnect (you can for example write some script that checks periodically if the connection is active and reconnects if it's not).

As a next step, if the ssh server on external.server is configured to accept outside connections to tunneled ports (this requires the option GatewayPorts yes to be present in /etc/ssh/sshd_config file on external.server; the default is no), you can connect directly to your PC from outside by connecting to portnumber on external.server, like below:

ssh -p portnumber [email protected]

where localuser is your username on your PC (not the external server!)

However, if the external server is not configured to accept outside connections to tunneled ports (which is far more common as this is the default), you need to make the connection in two steps.

First, log in to the external server as you would normally:

ssh [email protected]

Once logged in to external.server, type the following command (on the server):

ssh -p portnumber localuser@localhost

where localuser is your username on your PC, and "localhost" is literally localhost. You should be logged in to your PC now.

Answer 2

To access your Ubuntu PC's terminal from another computer, you can set up Secure Shell (SSH) server on your Ubuntu machine. SSH allows you to remotely connect to your computer and access the terminal over a secure connection. Here's how you can set it up:

1. Install SSH server: On your Ubuntu PC, open a terminal and run the following command to install the OpenSSH server:

sudo apt update
sudo apt install openssh-server

2. Configure SSH: Once the installation is complete, you can modify the SSH server configuration if needed. The configuration file is located at /etc/ssh/sshd_config. You can use a text editor like nano to make changes:

sudo nano /etc/ssh/sshd_config

By default, SSH should work fine, but you may want to check if password authentication is enabled (PasswordAuthentication yes) or if you want to allow root login (PermitRootLogin).

3. Enable SSH service: To start and enable the SSH service, run the following command:

sudo systemctl enable ssh
sudo systemctl start ssh

4. Find the IP address of your Ubuntu PC: To connect to your PC remotely, you need to know its IP address. Run the following command to find the IP address:

ip addr show | grep inet

Look for the line that starts with "inet" and contains your IP address (e.g., inet 192.168.0.100). Note down this IP address.

5. Configure port forwarding on your router: Access your router's configuration page. This is typically done by entering your router's IP address (e.g., 192.168.0.1) in a web browser and logging in with your router's credentials. The specific steps may vary depending on your router model, but you're looking for the "Port Forwarding" or "Virtual Servers" section.

   • Create a new port forwarding rule with the following information:
     • External (WAN) port: Choose a port number of your choice (e.g., 2222).
     • Internal (LAN) IP address: Enter the internal IP address of your Ubuntu PC (e.g., 192.168.0.100).
     • Internal (LAN) port: Here you will have to choose whether to leave the default value 22 or change the default port. For security reasons it would be best to change the default port as described at the end of this answer.
   • Save the configuration and exit the router settings.

6. Find your public IP address: To connect to your Ubuntu PC from another computer, you need to know your public IP address. Open a web browser on the Ubuntu PC or any other device and search for "What is my IP address" Note down the public IP address displayed.

7. Connect from another computer: (Apparently you are already clear on this aspect but for completeness I am writing it down) On the remote computer or mobile device, open a terminal or SSH client and run the following command:

ssh username@public-ip-address -p port-number

Replace username with your Ubuntu PC's username and public-ip-address with your router's public IP address, and port-number with the port number you chose in step 5.

8. Authenticate and connect: When prompted, enter your Ubuntu PC's password to authenticate. Once authenticated, you will have access to your Ubuntu PC's terminal from the remote computer.

Note: Make sure your Ubuntu PC has a static IP address or a DHCP reservation to ensure the IP address doesn't change over time. This will help you maintain a consistent connection.

Please note that exposing your SSH server to the internet carries some security risks. Ensure you have strong passwords, consider using key-based authentication, change the default SSH port (22) to a different port, and monitor your server's logs for any suspicious activity.

Answer 3

I have wrapped the solution described in the accepted answer (with automatic reconnect and strictly confined SSH login on the middleman server) in a small packaged solution that I have been using for a while.

sshrew runs as a service on the client, which connects, using certificate authentication, to a restricted shell on the "middleman SSH server".

On the server, the incoming connection (a) opens a reverse tunnel back to the client (or any machine in the client network), and (b) enters a bash script (the 'entry point'), where it goes to sleep and periodically wakes up to check that the client is still reachable through the tunnel.

When the tunnel appears shut, the entry point script terminates, which terminates the client's SSH connection. This is eventually detected by the client (note that interruptions in an SSH connection aren't immediately obvious to either end), which will then attempt to reconnect to the server