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2️⃣ SSH without IP

Jul 22, 20245 min read

SSH to Your Remote Server without IP

This article doesn’t intend to specify the details of the SSH Remote procedure. It’s merely a step-by-step tutorial. I believe it would be clearer to keep the steps straightforward.

Checking on the remote server

✅ Ensure the SSH service is running

Check the status of the SSH service:

sudo systemctl status ssh

The output shows the status info of the SSH service, with the text Active: active (running)indicating that the SSH service is running on the server.

✅ Check the SSH port number

Keeping the default SSH port at 22 is convenient for personal use if security isn’t a concern.

So let’s check the SSH configuration file that contains the port number:

grep Port /etc/ssh/sshd_config

The following output indicates that the SSH service is listening on the default port 22.

#Port 22

✅ Find the <remote_server_username>

Run the following command:

whoami

It will print out the username

train # ← it is the `<remote_server_username>`

✅ Find the public IP address as <remote_server_public_ip>

Run the following command:

curl https://icanhazip.com

It will print out the public IP of my server

172.16.254.3 # ← it is the `<remote_server_public_ip>`

Checking on the Local Machine

✅ Generate SSH Key Pair:

Run the following command:

ssh-keygen

✅ Authenticate local machine to remote machine

Run the following command:

ssh-copy-id <remote_server_username>@<remote_server_public_ip>

The two variables <remote_server_username> and <remote_server_public_ip> were mentioned before.

It’s my first time connecting to the remote server. My SSH client displays a prompt about the remote server’s authenticity and fingerprint information.

The authenticity of host '<remote_server_public_ip> (<remote_server_public_ip>)' can't be established.
ECDSA key fingerprint is SHA256:Jw/3FIJwpp3FIJw/3FIJw/3FppLVppmjWs.
Are you sure you want to continue connecting (yes/no/[fingerprint])?

Typing yes and pressing Enter will:

  • Allow the SSH client to accept the remote server’s host key.
  • Add the remote server’s host key to the know_host file in my local machine’s .ssh directory.

Then my SSH client display another prompt for requiring to enter the password.

<remote_server_username>@<remote_server_public_ip>'s password:

After entering the correct password just one time, ssh-copy-id copies my public key to the remote server’s ~/.ssh/authorized_keys file. And I will never entering password when I want to connect server with SSH.

Connect Remote Server

Run the following command:

ssh <remote_server_username>@<remote_server_public_ip>

SSH Login without the IP

✅ Editing SSH config file

1️⃣ Create ~/.ssh/config file, or edit it if the file exists.

2️⃣ Use the following format to add my <alias_name>, <remote_server_public_ip>, remote_server_username.

Host <alias_name>
	HostName <remote_server_public_ip>
	User <remote_server_username>

3️⃣ save the file.

✅ Connecting Only with Alias Name

Just typing ssh <alias_name> on the local machine allows me to connect my remote server without having to remember any of its details from now on! Quite a relief for the mental burden, right?

Summary

The content above covered the steps and detailed explanations. Now, let’s briefly review all the steps for a quick setup in a real-world environment.

Preparation checklist:

  • The <remote_server_username>: such as train
  • The <remote_server_public_ip>: such as 172.16.254.31
  • The SSH <alias_name>: such as mylinuxlab

Step 1: Run sudo systemctl status ssh

Step 2: Run ssh-keygen.

Step 3: Run ssh-copy-id train@172.16.254.31.

Step 4: Edit file ~/.ssh/config as following and save it.

Host trainlinuxlab
	HostName 172.16.254.31
	User train

Step 5: Run ssh trainlinuxlab.

Step 6: Close SSH connection by typing exit and Enter.

So I Think I Know SSH?

Connecting to a remote server using SSH is relatively straightforward.

However, the scenario becomes more complex when looking into aspects such as configuration, and security.

If I want to get the hang of SSH skills, the next aspects of SSH knowledge I should learn include:

  • Learn how to configure the SSH config file
  • Learn common SSH options
  • Grasp SSH security best practices

Maybe the title of my next article about SSH will be “So I Think Know SSH” 😃😃😃.

Q & A

Q: what is systemctl?

A: systemctl is a command line to control and manage the systemd system. The ctl is short for “control”.

Q: What does ssh-keygen do?

A: It generates an RSA key pair by default. This key pair contains a public key and a private key, which are stored in ~/.ssh/ directory.

Q: what are ~/.ssh/id_rsa.pub and ~/.ssh/id_rsa?

A: ~/.ssh/id_rsa.pub and ~/.ssh/id_rsa are the public and private keys generated by running ssh-keygen. The local machine’s public key is used to be shared and copied to the SSH service of the remote server. The local machine’s private key is used to authenticate the local machine to the remote systems that have the local machine’s public key.

****### Q: What is sshd? A: The sshd stands for OpenSSH Server Daemon.

Q: What is /etc/ssh/sshd_config?

A: It is a configuration file for the sshd.

Q: What does ssh-copy-id do?

A: It will copy the local public key to the autorized_keys file on the remote server.

Q: How to close the SSH connection?

A: Type ssh and press Enter.

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