Basic Linux Commands

Linux Commands

Linux command‑line tools are the backbone of reconnaissance, exploitation, and post‑exploitation on Unix‑like systems.

Common Commands

Navigation & File Management

Command	Description	Usage
pwd	Print working directory	pwd [OPTIONS]
cd	Change directory	cd [DIRECTORY]
ls	List directory contents	ls [OPTIONS] [FILE...]
mkdir	Create directory	mkdir [OPTIONS] DIRECTORY
rmdir	Remove empty directory	rmdir DIRECTORY
cp	Copy files or directories	cp SOURCE DEST
mv	Move or rename files/directories	mv SOURCE DEST
rm	Delete files or directories	rm [OPTIONS] FILE...
touch	Create empty file or update timestamp	touch FILENAME
ln	Create hard or symbolic links	ln [OPTIONS] TARGET LINK_NAME
find	Search for files and directories	find [PATH] [OPTIONS] [EXPRESSION]
chmod	Change file permissions	chmod [OPTIONS] MODE FILE
chown	Change file ownership (user)	chown [OPTIONS] USER FILE
chgrp	Change group ownership	chgrp [OPTIONS] GROUP FILE
umask	Set default file permission mask	umask [MASK]
tar	Archive files into tarball	tar -czf ARCHIVE.tar.gz FILES
gzip	Compress files using Gzip	gzip FILE
zip	Compress files into ZIP archive	zip ARCHIVE.zip FILES

Viewing & Text Processing

Command	Description	Usage
cat	Concatenate & display files	cat [OPTIONS] FILE...
less	Paginate large files	less FILE
more	View file one page at a time	more FILE
head	Show first lines of a file	head [OPTIONS] FILE
tail	Show last lines / follow file	tail [OPTIONS] FILE
grep	Search for patterns	grep [OPTIONS] PATTERN FILE
awk	Pattern scanning & processing language	awk 'pattern { action }' FILE
sed	Stream editor for filtering & transforming text	sed [OPTIONS] 'SCRIPT' FILE
cut	Remove sections from each line	cut [OPTIONS] FILE
tr	Translate or delete characters	tr SET1 SET2
sort	Sort lines of text files	sort [OPTIONS] FILE
uniq	Filter out repeated lines	uniq [OPTIONS] FILE
wc	Count lines, words, bytes	wc [OPTIONS] FILE
nl	Number lines of a file	nl FILE
diff	Show differences between files	diff FILE1 FILE2
tee	Read from stdin and write to file and stdout	tee FILE

System & User Info

Command	Description	Usage
whoami	Show current user	whoami
id	Display user/group IDs	id [USERNAME]
df	Disk usage overview	df [OPTIONS]
du	Show disk usage for files/directories	du [OPTIONS] [PATH]
uptime	Show how long the system has been running	uptime
uname	System information (kernel, OS, architecture)	uname -a
hostname	Show or set system hostname	hostname
date	Display or set system date/time	date
cal	Display a calendar	cal
env	Show environment variables	env
set	Display shell variables and functions	set
history	List previously executed commands	history
ps	Display running processes	ps aux
top	Real-time system process monitor	top
kill	Terminate process by PID	kill [-9] PID
pkill	Kill processes by name	pkill PROCESS_NAME
pgrep	Search for processes by name	pgrep PROCESS_NAME
w	Show who is logged in and what they are doing	w
who	Show who is logged in	who
last	Show login history	last
free	Show memory usage	free -h

Networking

Command	Description	Usage
ping	Test network connectivity (ICMP)	ping [OPTIONS] DESTINATION
curl	Retrieve data from URLs / APIs	curl [OPTIONS] URL
ssh	Secure remote shell & tunnelling	ssh [OPTIONS] USER@HOST

Help & Documentation

Command	Description	Usage
man	Read manual pages	man COMMAND
echo	Display text / variables	echo [STRING]

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Examples

Print Working Directory

pwd

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Change Directory

cd /var/www

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List All Files (long + hidden)

ls -la

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Create Directory

mkdir backups

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Remove Empty Directory

rmdir backups

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Copy File

cp secrets.txt /tmp/secrets.bak

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Move & Rename

mv old.log archive/old.log

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Force‑Delete Directory

rm -rf /tmp/testdir

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Show File Contents

cat /etc/passwd | grep ":/bin/bash"

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View Large Log

less /var/log/auth.log

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First 10 Lines

head -n 10 notes.txt

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Follow File Growth

tail -f /var/log/nginx/access.log

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Search Pattern

grep -R \"passwd\" /etc

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Current User

whoami

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User & Group IDs

id

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Human‑Readable Disk Usage

df -h

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Show Last 20 Commands

history | tail -n 20

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Ping Host 4 Times

ping -c 4 example.com

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Download Web Page

curl -o index.html http://example.com

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SSH on Custom Port

ssh -p 2222 user@target

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Read Manual Page

man ssh

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Write to File

echo \"hacked\" > /tmp/proof.txt

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See Also

• Bash Scripting Basics
• Privilege Escalation
• Netcat