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Chmod Calculator

Calculate Unix file permissions with an interactive chmod calculator. Toggle permission bits and get the numeric value.

chmod 644

What is a Chmod Calculator?

A chmod calculator is a visual tool that helps you determine the correct Unix/Linux file permission values without memorizing octal numbers. File permissions control who can read, write, and execute files on your server — getting them wrong can create security vulnerabilities or break your application.

The chmod command uses a three-digit octal number where each digit (0-7) represents permissions for the owner, group, and others. Each permission type has a numeric value: read (4), write (2), and execute (1). Our calculator lets you toggle checkboxes and instantly see the corresponding numeric value, eliminating guesswork.

How to Use This Chmod Calculator

  1. Toggle permission checkboxes for Owner, Group, and Others
  2. Select Read (r), Write (w), and/or Execute (x) for each category
  3. The numeric value updates in real time — use this in your chmod command
  4. Common presets: 755 (standard for directories), 644 (standard for files), 600 (private files)

Common Use Cases

  • Setting web server permissions — Configure correct permissions for Apache/Nginx document roots (typically 755 for directories, 644 for files)
  • Securing SSH keys — SSH requires private keys to be chmod 600 — no group or other access
  • Deploy scripts — Make shell scripts executable with chmod 755 deploy.sh
  • Fixing “Permission denied” errors — Quickly calculate what permissions your files need
  • WordPress/CMS setup — Set correct permissions for wp-config.php (640) and upload directories (755)

Frequently Asked Questions

What does chmod 777 mean and why is it dangerous?

chmod 777 gives full read, write, and execute permissions to everyone — owner, group, and all other users. This is a security risk on shared servers because any user can modify or execute the file. Use more restrictive permissions like 755 or 644 instead.

What’s the difference between chmod 755 and 644?

755 (rwxr-xr-x) allows the owner full access and others to read and execute — ideal for directories and scripts. 644 (rw-r–r–) allows the owner to read/write and others only to read — standard for regular files.