Read (r) Write (w) Execute (x)
Owner
Group
Others (Public)
-rw-r--r--

Detailed Permission Explanation

Command Examples

Numeric chmod 755 file
Symbolic chmod u=rwx,g=rx,o=rx file

Calculate CHMOD Permissions | Visual Linux & Unix Permissions Guide

Fix "Permission Denied" errors instantly. This tool helps you visualize Unix/Linux file permissions, convert between numeric and symbolic formats, and understand exactly what each setting does in plain English.

💡 Why CHMOD Matters

CHMOD (Change Mode) controls who can read, write, or execute files on your system. Stop guessing at values like 755 or 644. Use this tool to: - Visualize access levels for Owners, Groups, and Public users. - Translate symbolic strings (like -rwxr-xr-x) into numeric codes. - Enforce the "Principle of Least Privilege" to keep your server secure.

📘 How to Use This Tool

  • Toggle the Interactive Grid: Click checkboxes for Owner, Group, and Others to see live updates in all formats.
  • Paste Symbolic Strings: Input strings like u=rwx,g=rx,o=r to decode existing configurations.
  • Preview ls -l: See the exact string as it appears in your Linux terminal.
  • Identify Security Risks: The tool automatically flags dangerous settings (like 777 or world-writable bits) to help you protect your data.

🧐 Frequently Asked Questions

Q: When should I use 777? A: Almost never. Setting a file to 777 means anyone on the system can modify or delete it. While often used as a "quick fix" for permission errors, it creates a massive security hole. Use 755 for directories or 644 for files instead.

Q: What does the "Execute" (x) bit do for directories? A: For files, it allows them to run as programs. For directories, it allows a user to "enter" the directory (e.g., using cd). Without the execute bit, you might be able to list the files in a folder, but you won't be able to access them.

Q: Numeric vs. Symbolic: which is better? A: Numeric (755) is faster to type and the industry standard for documentation. Symbolic (u+x) is more precise when you want to change one specific bit without overwriting the rest of the file's configuration.

📚 Technical Trivia

The octal (numeric) system used in chmod represents a 3-bit binary sequence for each user category: - 4 (Binary 100) = Read - 2 (Binary 010) = Write - 1 (Binary 001) = Execute

By adding these bits, you get a single digit between 0 and 7. This elegant system was designed at Bell Labs in the early days of Unix and has remained the global standard for over 50 years.