Table of Contents

1. Introduction
2. SSH Configuration File

Introduction

When you first start using SSH with passwordless logins or just using your own private RSA key everything will work perfectly, but once you start creating different private keys for online services you will run into problems. By default the SSH client will scan your .ssh folder and try all the keys in there but after a couple tries the SSH server will stop accepting tries.

SSH Configuration File

If you also have the same problem as above, you should probably setup your SSH configuration file, in here you can define every single key for the host or even a subnet of hosts.

Create a file called “config” in your ~/.ssh/ directory. (~ refers to your home directory)

The syntax is really simple, let’s take a look.

Host example
  Hostname 127.0.0.1
  IdentityFile ~/.ssh/id_rsa
  IdentitiesOnly yes
  User samy

Name	Description
Host	this is a name that you can define yourself, use something memorable that describes the instance that you want to connect to. It’s similar to using your own DNS entries, you could also change your /etc/hosts but this file will only apply to SSH.
Hostname	the hostname or IP-adress of the server.
IdentitiesOnly	set to “yes” to use a RSA key instead of a password.
IdentityFile	your private key, this will probably be in you .ssh folder with an accompanying file that ends with .pub
User	The user used to login to the SSH server.

An example if you only want to use passwords is:

Host example
	Hostname 127.0.0.1
	PreferredAuthentications password
	PubkeyAuthentication no
  User samy

You can also define settings for all servers with a wildcard.

Host *
    ServerAliveInterval 300
    ServerAliveCountMax 2