🐧 Linux Basics You MUST Know Before AWS

Think of Linux commands in 8 core groups.

1️⃣ File & Directory Commands (MOST USED)

📂 pwd

pwd

Shows current directory

📌 Used when navigating EC2.

📂 ls

ls
ls -l
ls -la

📌 Used all the time.

📂 cd

cd /var/log
cd ~
cd ..

📌 Move between directories.

📄 touch

touch file.txt

Creates empty file.

📄 cat

cat file.txt

Show file content.

📄 less (IMPORTANT)

less file.txt

Scroll large files (logs).

Keys:

• q → quit
• / → search

📄 head / tail

head file.txt
tail file.txt
tail -f /var/log/messages

📌 tail -f = live logs (AWS debugging).

📂 mkdir

mkdir logs
mkdir -p app/data

📂 rm

rm file.txt
rm -r folder
rm -rf folder

⚠ Dangerous:

• -r → recursive
• -f → force

📂 cp

cp file1 file2
cp -r dir1 dir2

📂 mv

mv old.txt new.txt
mv file.txt /tmp/

Rename OR move.

2️⃣ File Permissions & Ownership (AWS CRITICAL)

🔐 chmod

chmod +x script.sh
chmod 755 script.sh

📌 Used for:

• Scripts
• User-data
• Deployments

👤 chown

sudo chown ec2-user:ec2-user file.txt

📌 Fix permission errors in EC2.

👀 whoami

whoami

Shows current user.

👀 id

id

Shows UID, GID.

3️⃣ User & Privilege Commands

🔑 sudo

sudo yum install nginx

📌 Required for:

• Installing packages
• Starting services
• Editing system files

👥 su

su -

Switch to root (not recommended often).

4️⃣ Package Management (Already Covered – Quick List)

Amazon Linux

yum install
yum remove
yum update
dnf install

Ubuntu

apt update
apt install
apt remove

📌 Used in user-data scripts.

5️⃣ Service Management (systemd)

🔧 systemctl

systemctl start httpd
systemctl stop httpd
systemctl restart httpd
systemctl enable httpd
systemctl status httpd

📌 AWS = services must survive reboot.

📜 journalctl

journalctl -u httpd
journalctl -u httpd -f

📌 Debug EC2 issues.

6️⃣ Networking Commands (AWS IMPORTANT)

🌐 ip

ip a

Shows IP address.

🌐 ss

ss -tuln

Shows listening ports.

🌐 curl

curl http://localhost

📌 Test web server.

🌐 ping

ping google.com

📌 Check connectivity.

🌐 netstat (older)

netstat -tuln

7️⃣ Process Management

⚙ ps

ps aux

⚙ top

top

📌 Monitor CPU & memory.

⚙ kill

kill PID
kill -9 PID

📌 Stop stuck processes.

8️⃣ Disk & Memory Commands

💾 df — Disk Free (EBS usage)

df -h

What df means

• df → Disk Free
• shows disk space per filesystem

-h flag

• -h → human-readable
• Shows sizes in GB / MB instead of bytes

💾 du — Directory size

du -sh /var/log # shows size of /var/log

What du means

• du → Disk Usage
• Shows how much space files/directories consume

Flags explained

• -s → summary only (not every file)
• -h → human-readable

💾 free — RAM usage

free -m 

• Shows memory (RAM) usage
• -m flag:Displays values in MB

💾 lsblk — List block devices (EBS volumes)

lsblk   # lists all block devices

📌 Used when attaching EBS volume.

9️⃣ Search & Text Processing (Logs)

🔍 grep

grep error app.log
grep -i error app.log

📌 MOST used for logs.

🔍 find

find / -name app.log

🔟 SSH & Remote Access

🔐 ssh

ssh -i key.pem ec2-user@IP

🔐 scp

scp file.txt ec2-user@IP:/home/ec2-user/

1️⃣1️⃣ Environment & Shell Basics

🌱 env

env

🌱 export

export APP_ENV=prod

📌 Used in deployments.

🌱 echo

echo $APP_ENV

1️⃣2️⃣ AWS User-Data Script Essentials

#!/bin/bash
yum update -y
yum install httpd -y
systemctl start httpd
systemctl enable httpd

📌 Requires:

• chmod +x
• Correct commands