CIS241

System-Level Programming and Utilities

Linux Filesystems

Erik Fredericks, frederer@gvsu.edu
Fall 2025

Based on material provided by Erin Carrier, Austin Ferguson, and Katherine Bowers

Time to become a terminal wizard

The *nux filesystem

Heirarchical

• Think of it like a tree

Important directories

Root: /

Your home directory: /home/username

• Shortcut to your home: ~

For example, to change the current directory to your home directory:

• cd /home/username or
• cd ~

Paths

We have relative and absolute

Absolute paths - start from the root of the filesystem (/)

• You can easily access these from anywhere

Relative paths - start from your current location (.)

• You have to know where you are in the current filesystem!
  • E.g., what folder you are in
  • The command that tells you is pwd (print working directory)

Useful tip - tab expansion

If you hit tab the shell will try to autocomplete for you

• Avoid typing in those pesky filenames
• E.g., cd /home/fre -> tab -> autoexpands to cd /home/frederer

If the file/path is ambiguous, double-tap tab to get a list of options

More important directories

• .: current working directory
• ..: parent of current directory

What is this? ./../../

Common commands (with basic usage)

• cd: Change to another directory
  • Usage: cd directory
• ls: List contents in directory
  • Usage: ls for current directory or ls directory for somewhere else
    • Is there a difference between ls and ls .?
• mkdir: Make directory
  • Usage: mkdir newdirectory | Example: mkdir /home/frederer/mynewdirectory/
• pwd: Show current working directory path
• touch filename: Create an empty file

Try all of these!!!

How on earth do you remember all this?

Practice!

• Also, more practice!

Check the man pages!

Search with apropos

• apropos "remove file"
• apropos "remote"
• apropos "ssh"

Some practice

1. Create a directory in the /tmp folder

• /tmp is scratch space shared by all on the machine and is regularly deleted

2. Create a directory named CIS241 in your user directory on EOS

3. Navigate to the new CIS241 folder in your user directory and create an empty file called TODO

• Interestingly, Linux doesn't care about extensions.
  • They're only used to help out in the desktop environment
  • File type is determined by the inner header within the file

More commands!

Use these with caution - deleting / overwriting files in Linux cannot be reversed/undone

• There is no recycle bin in the shell!

• rm: Remove file/directory (i.e., delete forever)

  • Usage: rm file

• cp: Copy file/directory (i.e., copy and paste)

  • Usage cp file1 file2

• mv: Move file/directory (i.e., cut and paste)

  • Usage: mv file1 file2

• cat file: Output the contents of a file

Command options (or flags, or arguments, ...)

Most terminal commands accept arguments to change its behavior

Typically delineated with a dash (by convention)

E.g.,:

• ls -la
  • Equivalent to ls -l -a
  • Meaning, give me the long listing and all information (i.e., hidden info)
• cp -r
  • Recursively copy (or, how you copy directories and their contents)

Options can be found typically by adding --help or reading the man pages

THE MANUAL

Linux commands often have an accompanying manual!

• man <cmd>
  • man cp
  • man ls

Some more practice: bashcrawl

Intended to give you practice navigating in a video game setting

• Reminiscent of classic terminal games (like Zork)!

I have installed it to my user directory on EOS

• Read-only so that it can't be destroyed
  • You can find it in /home/frederer/CIS241/public/bashcrawl
• However, you can pull down a copy yourself!
  • bashcrawl: https://gitlab.com/slackermedia/bashcrawl