SSH is an encrypted protocol used to connect between two systems. It’s widely used to gain access to remote server and run shell commands. It is also a common thing we use with VCS like github, gitlab etc.

SSH Key Generation

Creating ssh key is pretty simple, the CLI generates a public and private key pair. The public key is shared with the server and the private key is kept secret.

ssh-keygen -t rsa -b 4096

By default, we get a private key id_rsa and public key in ~/.ssh directory.

Using SSH

Before connecting, we need to add the public key to the server. We can do this by copying the public key to the server

  • add the public key to ~/.ssh/authorized_keys file on the server.
cat ~/.ssh/ | ssh username@server_ip "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"


  • using ssh-copy-id
ssh-copy-id username@server_ip

To establish a connection to a remote server, we use the ssh command followed by the username and the server IP address.

ssh username@server_ip

This will connect to the server

If the key is not successfully added to the server, the server will prompt for the password.

Using Multiple SSH Keys

We can also configure to use multiple ssh keys for different servers. This can be done by adding the following configuration to ~/.ssh/config file.

For example, if we have different keys for gitlab and github, we can add the following configuration to ~/.ssh/config file.

    User git
    IdentityFile ~/.ssh/id_rsa_gitlab

    User git
    IdentityFile ~/.ssh/id_rsa_github

Debugging SSH

If we are facing issues with the ssh connection, we can use the -v flag to get more information about the connection.

ssh -v username@server_ip

This will print the debug information about the connection.

It will show which key is being used, which key is being offered, and the reason for the connection failure.

Debugging Network

We can discover the hosts by using host command.


Anyway, network debugging tools like ping, traceroute, mtr are another story.