Linux Commands for File & Network Security

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🐧 Linux Commands for File & Network Security

Security professionals mainly use Linux to:
✅ Protect files
✅ Monitor users
✅ Control permissions
✅ Scan networks
✅ Detect attacks

🔐 File Security Commands

📁 1️⃣ List Files with Permissions

ls -l

Shows:

-rwxr-xr--

Owner | Group | Others

🔑 2️⃣ Change Permissions

chmod 755 file.sh
chmod 600 secret.txt

  • 755 → executable

  • 600 → private file

👤 3️⃣ Change Ownership

chown user:group file.txt

🔍 4️⃣ Find Sensitive Files

find / -perm -4000 2>/dev/null

Finds SUID files (security risk).

📄 5️⃣ Check File Integrity

sha256sum file.txt

Used to verify file changes.

🗂️ 6️⃣ Monitor File Changes

stat file.txt

Shows access, modify time.

🔎 7️⃣ Search Inside Files

grep "password" file.txt

Finds keywords in files/logs.

👥 User & Access Security

👤 8️⃣ Check Logged-in Users

who
w

🔐 9️⃣ Check User Privileges

id
sudo -l

🚫 🔟 Lock User Account

passwd -l username

🌐 Network Security Commands

🌍 1️⃣ Check IP & Interfaces

ip a

📡 2️⃣ Test Connectivity

ping google.com

🔎 3️⃣ Scan Network (Legal use only)

nmap 192.168.1.1

Finds open ports.

🔌 4️⃣ Check Open Ports

ss -tulnp
netstat -tulnp

Shows listening services.

📥 5️⃣ Capture Packets

tcpdump -i eth0

Used for traffic analysis.

🔗 6️⃣ Check Connections

whois google.com

Gets domain info.

🔥 7️⃣ Firewall Control (UFW)

ufw status
ufw enable
ufw allow ssh
ufw deny 80

Controls network access.

📜 Log Monitoring (Security Core)

🧾 Check Login Attempts

cat /var/log/auth.log

🔍 Live Log Monitoring

tail -f /var/log/syslog

⚙️ Process Security

⚡ Check Running Processes

ps aux
top

❌ Kill Suspicious Process

kill -9 PID

🧠 Useful Security Combos

Find writable files:

find / -type f -perm -o+w 2>/dev/null

Check failed logins:

lastb

Check history:

history

🔐 Best Practices for Security Pros

✔ Use strong permissions
✔ Monitor logs
✔ Limit sudo access
✔ Scan open ports
✔ Enable firewall
✔ Verify file integrity

📝 Exam Short Notes

  • chmod controls permissions.

  • nmap scans ports.

  • tcpdump captures packets.

  • ufw manages firewall.

  • auth.log stores login info.

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