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01 — Linux Essentials

What you'll learn: how to move around Linux, read and change permissions, manage users and processes, and install tools — the survival skills every later chapter assumes. Prerequisites: 00 — Getting started. ⬅️ Course index

Most beginner frustration in hacking isn't the tools — it's missing Linux basics. Spend real time here; it pays off everywhere.

The filesystem — one big tree

Linux has no "C: drive." Everything hangs off a single root, written /. Key places:

Path What it holds
/ The root of everything
/home/kali Your home folder (your files); shortcut: ~
/etc System configuration files
/usr/share Shared data — wordlists live in /usr/share/wordlists
/tmp Temporary files (wiped on reboot)
/root The root user's home

Moving around

pwd                 # "print working directory" — where am I?
ls                  # list files here
ls -la              # long list, including hidden files (start with .) and permissions
cd /usr/share       # change directory
cd ~                # go home
cd ..               # go up one level
Tab completion is your best friend: type the first letters of a name and press Tab — Kali finishes it. Press it twice to see options.

Reading, creating, moving files

cat file.txt              # print a file
less file.txt             # scroll a file (q to quit)
head -n 20 file.txt       # first 20 lines
mkdir loot                # make a folder
touch notes.txt           # create an empty file
cp a.txt b.txt            # copy
mv a.txt archive/         # move (or rename)
rm file.txt               # delete (no recycle bin — be careful!)
nano notes.txt            # a simple text editor (Ctrl+O save, Ctrl+X exit)

Getting help

man nmap            # the manual for a command (q to quit)
nmap --help         # quick options
which nmap          # where is this tool installed?
When a tool confuses you, man <tool> or <tool> --help is the first move — not a web search.

Permissions — the thing beginners trip on

Every file has an owner, a group, and permission bits for read (r), write (w), execute (x). ls -la shows them: 

-rwxr-xr--  1 kali kali  1234 Jul 13 10:00 script.sh
- First block rwx = the owner can read/write/execute. - Next r-x = the group can read/execute. - Next r-- = everyone else can only read.

Make a script runnable (you'll do this constantly): 

chmod +x script.sh        # add "execute" permission
./script.sh               # run a script in the current folder
sudo runs a command as root when normal permissions aren't enough.

Users & sudo

whoami                    # who am I?
sudo whoami               # -> root (borrow admin powers)
id                        # your user + groups
You'll see sudo before scans that need raw network access (nmap -sS, tcpdump). If a tool says "Permission denied" or "you must be root," add sudo.

Processes — what's running

ps aux                    # every running process
top                       # live process viewer (q to quit); htop is nicer: sudo apt install htop
jobs                      # background jobs in this shell
kill <PID>                # stop a process by its ID
Ctrl+C                    # stop the command running in front of you
Ctrl+Z then bg            # pause it and send it to the background

Installing tools — apt

Kali uses apt to install software from its repositories: 

sudo apt update                 # refresh the list of available software
sudo apt install seclists       # install a package (here: extra wordlists)
apt search bloodhound           # find a package by name
Some tools come from Python (pipx install <tool>) or GitHub (git clone <url>) — later chapters show which.

Networking peek (full detail in chapter 03)

ip a                      # your IP addresses and interfaces
ping 192.168.56.20        # is a host reachable? (Ctrl+C to stop)

Redirecting output — save your work

nmap 192.168.56.20 > scan.txt        # save output to a file (overwrite)
nmap 192.168.56.20 >> scan.txt       # append to a file
nmap 192.168.56.20 | grep open       # send output INTO another command (a "pipe")
Pipes (|) are the heart of Linux power — chapter 02 goes deep.

Common beginner mistakes

  • rm has no undo. Double-check before deleting; never rm -rf a path you're unsure of.
  • Forgetting ./ to run a local script — Linux won't search the current folder by default.
  • Fighting permissions instead of using sudo (or vice-versa — not everything needs root).
  • Not using Tab completion — it prevents typos and is much faster.

✅ Practice task

  1. Make a folder ~/lab/scans, cd into it.
  2. Run ip a and save your Kali IP to a file: ip a > myip.txt, then cat myip.txt.
  3. Create hello.sh containing echo "hello from kali", make it executable, and run it.
  4. Use man ls, find what -t does, then run ls -lat.

Next

➡️ 02 — Terminal power: pipes, grep/find, tmux, and tiny scripts that turn commands into workflows.

Sources

  • The Linux Command Line (free): https://linuxcommand.org/tlcl.php
  • Kali Docs: https://www.kali.org/docs/
  • man pages — built into Kali: run man man