Day 05 — Advanced Linux Commands for DevOps

🎯 Goal

Learn how to monitor, debug, and operate real Linux systems using advanced commands.

These are the commands you use when:

• A server is slow
• A service is down
• Disk is full
• CPU is high

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🧠 Mental Model

A running Linux system can be understood as:

Processes + Memory + Disk + Network

Your job as a DevOps engineer is to:

• Inspect system state
• Find bottlenecks
• Take corrective action

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1️⃣ Login & Remote Access

ssh — Secure Shell

ssh user@server-ip

What it does:
Connects to a remote Linux machine securely.

Why it matters:

• Primary way to access servers
• Used in CI/CD, cloud, automation

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2️⃣ Disk Usage Commands

df — Disk Filesystem Usage

df -h

What it does:
Shows disk space usage across filesystems.

Column	Meaning
Size	Total disk
Used	Used space
Avail	Free space

Use case:

• Check if disk is full

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du — Directory Usage

du -sh *
du -h /var/log

What it does:
Shows space used by files/directories.

Use case:

• Find which folder is consuming disk

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3️⃣ Process Monitoring

ps — Process Snapshot

ps aux

What it does:
Shows all running processes.

Use case:

• Check if a service is running

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top — Real-time Monitoring

top

What it does:
Shows live CPU, memory, processes.

Use case:

• Identify high CPU/memory usage

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fuser — Who is using a file/port

fuser 8080/tcp

What it does:
Shows which process is using a port/file.

Use case:

• Debug port conflicts

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4️⃣ Process Control

kill — Stop process

kill PID
kill -9 PID

What it does:
Sends signals to processes.

Signal	Meaning
default	graceful stop
-9	force kill

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nohup — Run in background

nohup python app.py &

What it does:
Runs command even after terminal closes.

Use case:

• Run long jobs on servers

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5️⃣ Memory Monitoring

free — Memory usage

free -h

What it does:
Shows RAM usage.

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vmstat — System performance

vmstat 1

What it does:
Shows:

• CPU usage
• Memory
• I/O stats

Use case:

• Diagnose performance issues

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🧪 Day-5 Lab

# SSH (if server available)
ssh user@server-ip
 
# disk usage
df -h
du -sh *
 
# processes
ps aux | head
top
 
# find process using port
fuser 8080/tcp
 
# kill process
kill PID
 
# background job
nohup sleep 1000 &
 
# memory
free -h
vmstat 1

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🧠 Key Takeaways

• ssh = access servers
• df + du = disk debugging
• ps + top = process monitoring
• kill = control processes
• free + vmstat = memory & performance

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✅ Outcome

You can now:

• Log into remote servers
• Monitor disk usage
• Analyze running processes
• Debug port conflicts
• Manage processes
• Diagnose system performance

Next → Users & Groups Management 🚀