Permissions & Security (Chmod/Chown/ACLs/SELinux/AppArmor)

Stop fumbling with permission bits and use chmod reference

🧩 The Challenge

You’ve just finished hardening a new directory and now you’re staring at a row of web files, trying to remember if it was 644 or 664 for the group write access. I’ve wasted so much time manually calculating octal modes only to find out I messed up a digit and broke the whole site.

💡 The Fix

Use the reference flag instead of trying to memorize octal strings. It just copies the permissions from a file you already know is correct, so you stop guessing.

chmod --reference=/var/www/html/index.php /var/www/html/uploads/*

⚙️ Why It Works

By pointing at a known good file, you let the system mirror the mode, owner, and group exactly how you want them. It turns a manual task into a simple one-second operation.

🚀 Pro-Tip: Use this with find if you need to bulk fix a massive tree of mixed-up permissions.

Linux Tips & Tricks | © ngelinux.com | 9/3/2026