SSH.md

SSH guide

Generate an SSH key

# Generate SSH key with a comment "YOUR_NAME" on your home machine.
ssh-keygen -t ed25519 -C "YOUR_NAME"

Add your SSH pubkey to your VPS provider

Upload the SSH key generated above into the SSH form while setting up your server, so you can log into the server without a password.

On Linux SSH .pub is usually located at ~/.ssh/YOUR_NAME.pub

# Copy the pubkey to clipboard using a text editor
nano ~/.ssh/user.pub

# Or copy from the terminal
cat ~/.ssh/user.pub

Open your VPS provider and paste your SSH pub key into an SSH form.

SSH into your server

Once your server is built by the VPS provider, you can try to log into it.

# SSH into your server as root
ssh -i ~/.ssh/YOUR_SSH_KEY root@YOUR_SERVER_IP_ADDRESS
# Example:
ssh -i ~/.ssh/user root@20.21.03.01

You should get the following message, type yes and press enter to add the server key fingerprint to your known hosts.

The authenticity of host 'YOUR_SERVER_IP_ADDRESS' can't be established.
ED25519 key fingerprint is SHA256:YOUR_SERVER_FINGERPRINT.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes

Sometimes your connection might be closed:

Warning: Permanently added 'YOUR_SERVER_IP_ADDRESS' (ED25519) to the list of known hosts.
Connection closed by YOUR_SERVER_IP_ADDRESS port 22

Simply try to log in again with the same command.

# Example:
ssh -i ~/.ssh/user root@20.21.03.01

Note: try to log in again if you got error 'Broken pipe'.

If you got another error, then read the troubleshooting section below.

SSH Troubleshooting

Clean known hosts after rebuild

Note: skip this step if you've never logged into your server before.

Sometimes you can mess up the setup process, so it might be easier to rebuild your server and start the setup process from the scratch. However, you'll get an error when trying to SSH into a server that has been recently rebuilt.

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ED25519 key sent by the remote host is
SHA256:YOUR_SERVER_FINGERPRINT.
Please contact your system administrator.

In that case, don't forget to clean the ~/.ssh/known_hosts file from old key fingerprints before trying to SSH into your server because your server key fingerprint has changed after rebuild.

# '-R' deletes a pub key of your previous server build.
ssh-keygen -R YOUR_SERVER_IP_ADDRESS
# Example:
ssh-keygen -R 20.21.03.01

Then try to SSH into your server without sudo:

# SSH into your server as root
ssh -i ~/.ssh/YOUR_SSH_KEY root@YOUR_SERVER_IP_ADDRESS
# Example:
ssh -i ~/.ssh/user root@20.21.03.01

You should get the following message, type yes and press enter to add the server key fingerprint to your known hosts.

The authenticity of host 'YOUR_SERVER_IP_ADDRESS' can't be established.
ED25519 key fingerprint is SHA256:YOUR_SERVER_FINGERPRINT.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes