SSH key-based authentication

Useful commands and snippets when dealing with Linux

2023-10-12

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SSH Key

Create a new SSH key without a passphrase.

ssh-keygen -t rsa -b 4096

Copy the SSH key to the remote device you want to log in.

ssh-copy-id -i <ID_RSA> <USER@HOST>

SSH Config

Add the following snippet to your SSH config file which is located at ~/.ssh/config. This links the host address with a specific private key.

Host <IP_ADDRESS>
  User <USER>
  IdentityFile ~/.ssh/<PRIVATE_KEY>
  IdentitiesOnly yes

SSH Agent

Automatic start

Copy the following code snippet in your .bashrc file. This autostarts the SSH agent when you open a new shell.

function start_ssh_agent {
  eval $(/usr/bin/ssh-agent) > /dev/null
  /usr/bin/ssh-add ~/.ssh/<PRIVATE_KEY> 2> /dev/null
}

ps -ef | grep ${SSH_AGENT_PID} | grep ssh-agent$ > /dev/null || {
  start_ssh_agent;
}

NOTE: This code snippet is still a bit buggy. Adding a private keys with a SSH config is a better approach.

Manual start

To start the SSH agent manually run the following to commands.

eval $(ssh-agent)
ssh-add ~/.ssh/<PRIVATE_KEY>

Stop the SSH agent

To stop the SSH agent lookup the PID and kill the process.

ps aux | grep ssh-agent
kill <SSH_AGENT_PID>