CIS241

System-Level Programming and Utilities

SSH

Erik Fredericks, frederer@gvsu.edu
Fall 2025

Based on material provided by Erin Carrier and Austin Ferguson

First, Linux

What is it?

• Often referred to as an operating system (OS)

  • Competing with Mac/Windows

• Technically, it is a kernel

Many OSs use the Linux kernel

• Ubuntu (what is on EOS)
• Arch, Kali, Gentoo, Fedora, etc.

Isn't Mac Linux too?

• Nope, Darwin! (Unix-based)

Protection Rings

A bit of history

1970s: UNIX source code typically stripped from distribution

• Exorbitant amounts of money to acquire source

Linux first developed by Linus Torvalds to be a copy of UNIX

• Released it to Internet for suggestions on how to improve it

• Kernel only updated by core developers and from suggestions

• Short history of Linux

Unix?

Unix was an earlier operating system

• Linux and other systems are heavily influenced by Unix

We now use “Unix-like” to describe systems

• They follow the same general ideas as Unix
• This means most things (commands, properties) carry over!

"Unix-like" systems:

• Linux
• macOS
• FreeBSD
• Solaris

Unix Timeline

Windows

Windows (today), is not Unix-like

• Can you do your homework on a Windows machine?
• Not by default

However, we have WSL! (◕‿◕✿)

• Windows Subsystem for Linux
• If you are on Windows, you must install WSL
  https://learn.microsoft.com/en-us/windows/wsl/install
  • Be very happy about this - I dreamed about just having the ability to SSH from the terminal when in industry

Terminal

Shells (local)

See the little dollar sign?

Shell!

What shell are we using?

echo $0

Shells (local)

Where is the shell here?

• Ring 3, typically!

How do we run in other rings?

Shells (remote)

Or, connecting to another machine

• Or or, doing your homework ಠ_ಠ

ssh --> Secure Shell

Usage: ssh username@address

For example, connecting to EOS:

ssh username@eos1.cis.gvsu.edu

Lab fun

DO NOT

SHUT DOWN

THESE MACHINES