SSH config file in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of SSH config with Host alias

Given the following SSH config snippet, what is the output of ssh myserver if the server myserver.example.com is reachable and the user is alice?

Linux CLI

Host myserver
  HostName myserver.example.com
  User alice
  Port 2222

A Connects to myserver.example.com on port 2222 as user alice

B Connects to myserver.example.com on default port 22 as user alice

C Connects to myserver on default port 22 as current user

D Fails with unknown host error

💡 Hint

Look at how HostName, User, and Port are set under the Host alias.

The SSH config defines an alias myserver that points to myserver.example.com with user alice and port 2222. So ssh myserver uses these settings.

📝 Syntax

intermediate

Identify the syntax error in SSH config

Which option shows a syntax error in this SSH config snippet?

A Host example\n HostName example.com\n Port 2200

B Host example\n HostName example.com\n User bob

C Host example\n HostName example.com\n User

D Host example\n HostName example.com\n IdentityFile ~/.ssh/id_rsa

💡 Hint

Check if all directives have values.

Option C has User without a username value, which is invalid syntax.

🔧 Debug

advanced

Why does SSH ignore the Port setting?

Given this SSH config, why does ssh server1 connect on port 22 instead of port 2200?

Linux CLI

Host server1
  HostName server1.example.com
Host server*
  Port 2200

A The wildcard Host block is ignored because it comes after the exact match

B The first Host block overrides the Port setting because it matches exactly and has no Port line

C SSH always uses port 22 unless specified on the command line

D Port must be set before HostName to take effect

💡 Hint

SSH applies the first matching Host block and ignores later ones.

SSH uses the first matching Host block. Since server1 matches the first block exactly, it uses its settings. That block has no Port, so default 22 is used. The second block with Port 2200 is ignored for this host.

🚀 Application

advanced

Create SSH config for multiple hosts with shared settings

You want to connect to web1.example.com and web2.example.com as user deploy on port 2222. Which SSH config snippet achieves this with minimal repetition?

A Host web1 web2\n HostName %h.example.com\n User deploy\n Port 2222

B Host web*\n HostName %h.example.com\n User deploy\n Port 2222

C Host web1\n HostName web1.example.com\n User deploy\n Port 2222\nHost web2\n HostName web2.example.com\n User deploy\n Port 2222

D Host web1 web2\n HostName web1.example.com\n User deploy\n Port 2222

💡 Hint

Use Host aliases and %h to substitute hostnames.

Option A uses a single Host line with both hosts and uses %h to substitute the hostname part, avoiding repetition.

🧠 Conceptual

expert

Effect of Include directive in SSH config

If your main SSH config file contains Include ~/.ssh/config.d/*, what happens when you run ssh myhost?

A SSH reads all files in ~/.ssh/config.d/ and applies their settings before the main config

B SSH reads the main config first, then applies settings from all included files in order

C SSH ignores the Include directive unless you specify --include on the command line

D SSH merges settings from included files with the main config, applying them in the order they appear

💡 Hint

Think about how SSH processes multiple config files.

The Include directive merges settings from included files with the main config, applying them in the order they appear. This allows modular config management.