day-06-linux

06_Linux_Process_Management.md

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+# Linux – Process Management (Day 6)
+
+## What is a Process?
+A process is a running program in Linux.
+Every application or service runs as a process.
+
+---
+
+## Why Process Management is Important for DevOps?
+DevOps engineers must:
+- check if an app is running
+- monitor CPU and memory usage
+- stop or restart stuck applications
+
+Most production issues are process-related.
+
+---
+
+## View Running Processes
+
+### ps command
+```bash
+ps
+ps aux
+```
+
+a → all users  
+u → user format  
+x → background processes
+
+---
+
+## top Command
+Shows live CPU and memory usage.
+
+```bash
+top
+```
+
+Exit:
+```bash
+q
+```
+
+---
+
+## htop (If Installed)
+Better version of top.
+
+```bash
+htop
+```
+
+---
+
+## Find Process by Name
+```bash
+ps aux | grep nginx
+```
+
+---
+
+## Kill a Process
+
+### Normal kill
+```bash
+kill PID
+```
+
+### Force kill (DANGEROUS)
+```bash
+kill -9 PID
+```
+
+⚠️ Use kill -9 only if normal kill fails.
+
+---
+
+## Kill by Process Name
+```bash
+pkill nginx
+```
+
+---
+
+## Background & Foreground Jobs
+
+Run in background:
+```bash
+command &
+```
+
+Example:
+```bash
+sleep 100 &
+```
+
+View jobs:
+```bash
+jobs
+```
+
+Bring to foreground:
+```bash
+fg
+```
+
+---
+
+## Check Process Using a Port
+```bash
+sudo netstat -tulnp
+```
+or
+```bash
+sudo ss -tulnp
+```
+
+---
+
+## Real DevOps Scenario
+Problem: App not responding
+
+Steps:
+1. Check if process is running
+2. Check CPU/memory usage
+3. Restart process
+
+Commands:
+```bash
+ps
+top
+kill
+```
+
+---
+
+## Common Mistakes
+- Killing wrong PID
+- Using kill -9 unnecessarily
+- Not checking process owner
+
+---
+
+## DevOps Rule
+✅ Inspect first  
+❌ Kill blindly
+
+---
+
+## Summary
+Today I learned Linux process management using ps, top, kill,
+and background jobs. These skills are essential for production servers.