DCubes
Linux module

Lesson 3

The filesystem is your data lake

Paths, home, and how to move around directories like a data server.

beginner30 minRun on your machine

What you will be able to do

  • Explain absolute vs relative paths and what ~ means
  • Use pwd, cd, and ls to move and look around
  • Recognize directories you will see on data servers

Why this matters for DE and AI

A “data lake” on a server is, at the bottom, directories on a disk. CSV dumps, Parquet partitions, model checkpoints, and log files all have a path. If you cannot move around a filesystem, you cannot debug a job that wrote to the wrong place.

Concepts

Linux (and macOS) organize files in a tree that starts at /, called root. Not the same as the administrator user named root.

/                  ← the top
├── home/          ← user folders on Linux
│   └── sam/
├── Users/         ← user folders on macOS
├── tmp/           ← throwaway files
├── var/log/       ← system and app logs on Linux servers
└── opt/           ← optional software, common on servers

On many data teams people also create /data for datasets. That is a convention, not a law.

Home and ~

Your home directory is yours. On Ubuntu/WSL it is /home/YOURNAME. On macOS it is /Users/YOURNAME.

~ is shorthand for that home. ~/dcubes/linux-lab is the lab folder.

Absolute vs relative paths

  • Absolute — starts at /. Same place no matter where you are. Example: /tmp.
  • Relative — starts from the directory you are in. Example: linux-lab when you are already in ~/dcubes.

pwd prints where you are. Always run it when you feel lost.

The three commands

Command Meaning
pwd Print working directory
cd PLACE Change directory to PLACE
ls List names in the current directory
ls -la List all files, including hidden ones, with details
cd or cd ~ Go home
cd - Go back to the previous directory
cd .. Go up one level

Hidden files start with a dot: .bashrc. ls hides them. ls -la shows them.

Tab completion: type the first letters of a folder and press Tab. The shell fills the rest if it is unique.

Practice on your machine

cd ~
pwd

What you should see: /home/YOURNAME or /Users/YOURNAME.

ls
ls -la

The second listing is longer. Names starting with . are configuration files. Do not delete them.

Go to the lab, then up, then back:

cd ~/dcubes/linux-lab
pwd
cd ..
pwd
cd linux-lab
pwd

Visit /tmp (a shared scratch folder) and return:

cd /tmp
pwd
ls
cd -
pwd

What you should see after cd -: you are back in linux-lab.

Try tab completion:

cd ~/dc<Tab>

It should expand toward dcubes.

Look at / without staying there:

ls /

On Linux you should see names like home, tmp, etc. On macOS you will see Users, Applications, tmp.

Common mistakes

  • cd ~/dcubes/linux-lab with a typo. The shell says No such file or directory. Run ls ~ and ls ~/dcubes to see what actually exists.
  • Confusing cd with ls. ls looks. cd moves. You can ls /tmp without going there.
  • Spaces in names. Avoid them in this module. If a name has a space, you must quote it: cd "My folder". Data pipelines also prefer names without spaces.

Next

Create and organize files — mkdir, touch, cp, mv, rm.

← Meet the terminalCreate and organize files →