Linux

Take control of your ssh configuration

Zachary Carciu •
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Take control of your ssh configuration

Secure Shell (SSH) is an essential tool for managing remote servers and devices. However, it can be painful to look up your different commandline options and make sure you’re not messing up some part of the command. The ssh_config file allows you to streamline and secure your SSH connections by defining reusable settings. We’ll also talk about how we can seamlessly interact with different remote git repo like Github, Gitlab and others.

Table of Contents

What is SSH Config?

The ssh_config file is a configuration file for the SSH client that allows you to set defaults for specific hosts, customize authentication methods, and configure connection options. It is found in:

  • Per-user configuration: ~/.ssh/config
  • System-wide configuration: /etc/ssh/ssh_config

Using this file, you can create short and readable host aliases, specify authentication keys, set ports, and even enable advanced features like proxying through jump hosts.

Basic SSH Config Syntax

Each configuration block begins with a Host directive followed by settings for that host. Example:

Host myserver
    HostName example.com
    User myuser
    Port 2222
    IdentityFile ~/.ssh/id_rsa

Now, instead of typing:

ssh -i ~/.ssh/id_rsa -p 2222 myuser@example.com

You can simply run:

ssh myserver

Common SSH Config Directives

Here are some commonly used settings:

DirectiveDescription
HostDefines a block for specific hosts; wildcards (*, ?) can be used.
HostNameThe actual hostname or IP address to connect to.
UserDefault username for login.
PortSpecifies the SSH port (default is 22).
IdentityFileDefines the SSH private key file to use.
ForwardAgentEnables SSH agent forwarding (yes or no).
ProxyJumpSpecifies an intermediate host (jump host) for proxying SSH connections.
ServerAliveIntervalSends a keep-alive packet every X seconds.
ServerAliveCountMaxNumber of failed keep-alive responses before disconnecting.

Advanced SSH Configurations

1. Configuring Github origins

If you connect to multiple remote servers, you can define each one separately:

Host github-work
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_github

Host workserver
    HostName 192.168.1.100
    User admin
    Port 2222

Now, you can connect to GitHub with:

git remote add origin git@github-work:company/ExampleRepo.git
git add .
git commit -m 'message'
git push origin master

And to your work server with:

ssh workserver

You can set up different remotes for different repos.

2. Wildcard Hosts

You can use wildcards to apply settings to multiple hosts:

Host *.example.com
    User myuser
    IdentityFile ~/.ssh/example_key

This configuration applies to server1.example.com, server2.example.com, etc.

3. Using a Jump Host (ProxyJump)

If a server is only accessible via an intermediate (bastion) host:

Host internal-server
    HostName 10.0.0.100
    User admin
    ProxyJump bastion-host

Now, running:

ssh internal-server

Will automatically route through bastion-host.

4. Disable Strict Host Key Checking

For temporary connections or testing environments:

Host testserver
    HostName test.example.com
    User testuser
    StrictHostKeyChecking no
    UserKnownHostsFile /dev/null

This prevents SSH from prompting about host key changes and avoids storing the host key.

Applying SSH Config Changes

After editing ~/.ssh/config, apply changes by running:

ssh -F ~/.ssh/config myserver

Or restart the SSH agent with:

ssh-add -D

Final Thoughts

Using SSH config effectively can save you time, improve security, and simplify managing multiple remote connections. Whether you’re setting up aliases, enabling SSH key authentication, or routing through a jump host, the ssh_config file is an essential tool for any developer or sysadmin.

Start optimizing your SSH workflow today! 🚀

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