SSH specify key: A guide to specifying SSH keys for secure authentication

ssh specify key

Secure Shell (SSH) is a widely used protocol for securely accessing remote servers and systems. One of the key components of SSH authentication is the use of public and private key pairs. In this article, we will explore the concept of specifying SSH keys and how it can help to enhance the security of your SSH connections. We will also provide code examples and related concepts to help you understand the topic better.

What is an SSH key pair?

Before we delve into specifying SSH keys, let’s first understand what an SSH key pair is. An SSH key pair is a set of two keys – a public key and a private key – that are used for authentication between a client and a server. The private key is kept on the client machine, while the public key is uploaded to the server. When the client attempts to connect to the server, the server uses the public key to verify the client’s identity. If the public key matches the private key on the client machine, the client is authenticated and granted access to the server.

SSH key pairs are widely used because they provide a more secure method of authentication compared to passwords. Passwords can be easily compromised through brute-force attacks or phishing attempts. SSH keys, on the other hand, are much harder to crack, making them a more secure option.

Specifying SSH keys

When using SSH to connect to a remote server, you can specify which key pair to use for authentication. By default, SSH will look for the key pair in the ~/.ssh directory on your local machine. However, if you have multiple key pairs, or if you have saved your key pair in a different location, you can specify which key pair to use.

To specify an SSH key, you can use the -i option followed by the path to your private key. For example:

ssh -i /path/to/private/key user@server

In this example, we’re using the ssh command to connect to a remote server. We’re specifying the -i option to indicate that we want to use a specific private key. We then provide the path to our private key file (/path/to/private/key). Finally, we provide the username and hostname of the remote server we want to connect to (user@server).

SSH agent

When using SSH, you may find yourself entering your passphrase multiple times if you have set one up for your private key. To avoid this, you can use an SSH agent. An SSH agent is a program that runs in the background and stores your private key. When you try to use your private key, the SSH agent automatically provides it, so you don’t have to enter your passphrase repeatedly.

To start an SSH agent, you can use the ssh-agent command:


This will start the SSH agent and display the process ID (PID) of the agent. You can then add your private key to the agent using the ssh-add command:

ssh-add /path/to/private/key

This will add your private key to the SSH agent, and you can then use the key without having to enter your passphrase repeatedly.

SSH config file

Another related concept is the SSH config file. The SSH config file is a configuration file that allows you to specify options for your SSH connections. You can use the SSH config file to specify which key pair to use for a particular host or set of hosts.

The SSH config file is located at ~/.ssh/config on your local machine. To specify a key pair for a particular host, you can add the following lines to your SSH config file:

    IdentityFile /path/to/private/key

In this example, we’re specifying that for the host, we want to use the private key located at /path/to/private/key.


SSH key pairs are an essential component of SSH authentication. By specifying which key pair to use for a particular connection, you can enhance the security of your SSH connections. We hope this article has provided you with a better understanding of how to specify SSH keys and related concepts such as the SSH agent and SSH config file.