Learn SSH: Config File

In this article series, I will explain how to use a command-line terminal to connect to secure shell (SSH) servers, using the config file for quick access to frequently used servers, and setting up an SSH server on macOS, Ubuntu, or CentOS.

Table of Contents:

– Introduction
– SSH CLI Commands
SSH Config File

SSH config file makes it easier to connect to frequently used servers. Here, I start with a simple server setup and then explain how to setup proxy jumps.

SSH config file is located in home directory under “.ssh” folder:

~/.ssh/config

For each server, add a block of text starting with “Host” followed by a memorable name for that server.

Host favorite_ssh

Add information like the address of the host on the following line with indentation:

Host favorite_ssh
        HostName ip_or_address_of_server
        User username_at_the_server

Now save the file. To connect to the sever, in a terminal window simply type ssh followed by the name you chose in the config file:

$ ssh favorite_ssh

This is equivalent of typing the following command:

$ ssh username_at_the_server@ip_or_address_of_server

You can add the identity file location to the config file as well:

Host favorite_ssh
        HostName ip_or_address_of_server
        User username_at_the_server
        IdentityFile ~/.ssh/my_private_key

which is equivalent of the following command:.

$ ssh username_at_the_server@ip_or_address_of_server -i ~/.ssh/my_private_key

You can add multiple servers to the config file:

Host favorite_ssh
        HostName ip_or_address_of_server
        User username_at_the_server
        IdentityFile ~/.ssh/my_private_key

Host favorite_ssh_2
        HostName ip_or_address_of_server_2 
        User username_at_the_server_2
        IdentityFile ~/.ssh/my_private_key_3

Host favorite_ssh_3
        HostName ip_or_address_of_server_3 
        User username_at_the_server_3
        IdentityFile ~/.ssh/my_private_key_3

You can add a proxy or jump server to the config file as well and use it to connect to your “favorite_ssh”:

Host proxy_1
        HostName ip_or_address_of_proxy_server
        User username_at_proxy_server
        IdentityFile ~/.ssh/proxy_server_private_key

Host favorite_ssh
        HostName ip_or_address_of_server
        User username_at_the_server
        IdentityFile ~/.ssh/my_private_key
        ProxyJump proxy_1

You can also use wildcards to use a same setting for a range of IP addresses (10.0.* and 10.1.0.*) :

Host proxy_1
        HostName ip_or_address_of_proxy_server
        User username_at_proxy_server
        IdentityFile ~/.ssh/proxy_server_private_key

Host 10.0.*
        User username_at_these_servers
        IdentityFile ~/.ssh/my_private_key_for_all_the_servers
        ProxyJump proxy_1


Host 10.1.0.*
        ProxyJump proxy_1

Now to connect to a server with IP address of 10.0.0.1, you can use the following command:

$ ssh 10.0.0.1

Or to connect to 10.1.0.2 with a username “my_user”, you can run:

$ ssh my_user@10.1.0.2

Let me know your questions and comments in the comment section.

Leave a Comment

Your email address will not be published. Required fields are marked *

%d bloggers like this: