Blog 6: Linux Permissions, SSH & Service Management – DevSecOps Foundations

By Kalyan Kalavena | 🛡️ All Rights Reserved

🧑‍💻 Why This Blog Matters

As a DevSecOps engineer, you’ll often deal with Linux file permissions, secure server access, and managing services like SSH or Nginx. These aren’t just admin tasks — they form the backbone of cloud security, automation, and infrastructure control.

🔐 1. File & Folder Permissions

Numeric System

Permission | Code | Meaning
r          | 4    | Read
w          | 2    | Write
x          | 1    | Execute
  

Example:

-rw-r--r-- 1 ec2-user ec2-user  myfile.txt

• Owner: Read & Write
• Group: Read only
• Others: Read only

Commands

chmod o+w file.txt
chmod o-r file.txt
chmod ugo+rwx file.txt
chmod 740 file.txt
  

🧑‍🚀 2. SSH Key-Based Login

Steps

1. Create .ssh directory
2. Set ownership to user
3. Create authorized_keys file and set permissions
4. Login using:

   ssh -i kalyan.pem kalyan@IP

📦 3. Package Management

dnf install nginx -y
dnf remove nginx
dnf list installed
dnf list available
  

🛠️ 4. Service Management

systemctl status sshd
systemctl start nginx
systemctl stop nginx
systemctl restart nginx
systemctl enable nginx
  

🔍 5. Process & Network Management

ps -ef | grep nginx
kill PID
kill -9 PID
netstat -lntp
  

✅ Summary

• chmod, chown = Control file access
• SSH key setup = Login without password
• dnf & yum = Manage software
• systemctl = Manage services
• kill & netstat = Monitor processes and ports

🛡️ By Kalyan Kalavena – All rights reserved. This blog is protected. No copying or edits allowed without permission.