SSH config file in Linux CLI - Commands & Configuration

Introduction

Managing multiple SSH connections can be confusing and slow if you have to type long commands every time. The SSH config file lets you save connection details so you can connect quickly with simple commands.

When you connect regularly to several servers and want to avoid typing full addresses and options each time

When you want to use different usernames or keys for different servers without remembering all details

When you want to simplify SSH commands for easier and faster access

When you want to set default options like ports or forwarding for specific hosts

When you want to organize your SSH connections neatly in one place

Config File - config

config

Host myserver
  HostName 192.168.1.100
  User admin
  Port 2222
  IdentityFile ~/.ssh/id_rsa_myserver

Host github
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa_github
  IdentitiesOnly yes

Host: A nickname for the server you want to connect to.

HostName: The real address or IP of the server.

User: The username to log in as.

Port: The port number if not the default 22.

IdentityFile: The private key file to use for authentication.

IdentitiesOnly: Ensures only the specified key is used.

Commands

Connects to the server using the saved settings in the SSH config file under the nickname 'myserver'. This saves typing the full address, port, and user.

Terminal

ssh myserver

Expected Output

Welcome to Ubuntu 20.04.4 LTS (GNU/Linux 5.4.0-104-generic x86_64)



admin@myserver:~$

Connects to GitHub using the nickname 'github' with the specified user and key from the config file.

Terminal

ssh github

Expected Output

PTY allocation request failed on channel 0

Hi username! You've successfully authenticated, but GitHub does not provide shell access.

Connection to github.com closed.

Shows the contents of your SSH config file so you can review or edit your saved connection settings.

Terminal

cat ~/.ssh/config

Expected Output

Host myserver

  HostName 192.168.1.100

  User admin

  Port 2222

  IdentityFile ~/.ssh/id_rsa_myserver



Host github

  HostName github.com

  User git

  IdentityFile ~/.ssh/id_rsa_github

  IdentitiesOnly yes

Key Concept

If you remember nothing else from this pattern, remember: the SSH config file lets you save and reuse connection details to connect faster and easier.

Common Mistakes

Not setting correct file permissions on the SSH config file

SSH ignores the config file if permissions are too open, causing connections to fail or ignore settings.

Set permissions with 'chmod 600 ~/.ssh/config' to keep the file private and usable.

Using incorrect indentation or syntax in the config file

SSH config requires indentation before options; wrong indentation causes errors or ignored settings.

Always indent options with spaces under each Host entry.

Forgetting to reload or re-run SSH after editing the config file

Changes won't apply until you start a new SSH session; old sessions keep using old settings.

Simply start a new SSH connection to apply changes; no special reload needed.

Summary

Create an SSH config file to save connection details like hostname, user, port, and keys.

Use simple nicknames to connect quickly without typing full commands.

Check and fix file permissions and syntax to ensure SSH uses your config correctly.