Linux Fundamentals — Day 4
Updated
•3 min read
H
Network Engineer with 3+ years of experience in infrastructure, system administration, and enterprise networking, currently transitioning into DevOps and Cloud Engineering.
Hands-on experience with Fortinet firewalls, routers, switches, Windows/Linux servers, and Hyper-V virtualization.
Currently building and learning with Docker, Kubernetes, AWS, Linux, CI/CD, GitHub Actions, and automation tools while leveraging MERN stack knowledge to understand the complete application lifecycle from development to deployment.
Passionate about cloud infrastructure, automation, containers, and modern DevOps practices. Regularly sharing my learning journey, projects, and hands-on experiments.
Processes + Monitoring + Background Jobs
This is real server administration.
You’ll learn how Linux manages:
running applications
CPU
memory
background tasks
killing stuck programs
These are daily DevOps skills.
1. What is a Process?
A process = running program.
Examples:
browser
Docker daemon
nginx
VS Code
bash terminal
Each process has:
PID (process ID)
memory usage
CPU usage
owner
2. View Running Processes
ps
# Shows processes in current shell.
ps aux (VERY IMPORTANT)
# Common real-world command.
ps aux
# a: Shows processes for all users on the system, not just the current user.
# u: Displays the output in a user-oriented format, providing detailed columns like CPU and memory usage.
# x: Includes processes without a controlling terminal, such as background daemons and system services that start at boot.
Shows:
user
PID
CPU
memory
command
3. Filter Processes
Find nginx process
ps aux | grep nginx
4. Process ID (PID)
Examples:
2315
# Every running process has unique PID.
5. Kill Process
Graceful stop
kill PID
# kill 2315
Force kill - Use carefully.
kill -9 PID
# ⚠️ Forcefully terminates process.
6. top (System Monitor)
top
Shows live:
CPU usage
memory
running processes
7. htop (Better top)
Install:
sudo apt install htop
# Run
htop
8. Background Jobs
Run in background
sleep 100 &
# & sends process to background.
Check jobs
jobs
9. Foreground & Background
Bring to foreground
fg
Send running process to background
Press:
Ctrl + Z
# Then
bg
10. nohup
Keeps process running after terminal closes.
nohup python app.py &
# Very common for servers.
# Output stored in:
# nohup.out
11. System Load
uptime
uptime
Shows:
running time
load average
12. Memory Usage
free
free -h
Shows:
RAM
swap
available memory
13. Disk Usage
df -h
# Shows filesystem usage.
du - Directory size.
du -sh folder/
14. CPU Information
lscpu
15. Open Ports
ss -tulnp
Shows:
listening ports
services
16. Real DevOps Examples
Find process using port 3000
ss -tulnp | grep 3000
Kill stuck node app
ps aux | grep node
kill -9 PID
Monitor logs live
tail -f app.log
Check high memory usage
top
17. Signals in Linux
Processes receive signals.
| Signal | Meaning |
|---|---|
| SIGTERM | graceful stop |
| SIGKILL | force kill |
| SIGSTOP | pause process |
18. Useful Shortcuts
Stop current process
Ctrl + C
Pause current process
Ctrl + Z
