Chmod Calculator
Visual Linux permissions generator. Convert between octal numeric codes (e.g. 755, 644) and symbolic notation (-rwxr-xr-x) instantly.
chmod 755 /path/to/target
Understanding Linux File Permissions
Unix-like operating systems (Linux, macOS, BSD) use the POSIX permission model to control read, write, and execution rights across three distinct user categories:
- Owner (u): The user account that created or owns the file.
- Group (g): A collection of users sharing collaborative rights.
- Others (o): Any unauthorized or anonymous system user (the public internet on a web server).
Production Security Best Practices
Never apply chmod 777 to resolve permission errors in production. Granting world-writable rights allows malicious scripts or compromised processes to overwrite code or inject webshells.
Folders: find . -type d -exec chmod 755 {} \;
Files: find . -type f -exec chmod 644 {} \;
Frequently Asked Questions
What does chmod 755 mean in Linux?
chmod 755 grants the file owner full read (4), write (2), and execute (1) permissions (4+2+1=7), while group members and all others receive read (4) and execute (1) permissions (4+1=5). It is the standard permission setting for web server directories and executable scripts.
What is the difference between chmod 777 and chmod 644?
chmod 777 gives every user on the system read, write, and execute permissions, posing severe security vulnerabilities. In contrast, chmod 644 allows the owner to read and write (4+2=6), while others can only read (4), making 644 the industry standard for web files (HTML, CSS, PHP, images).
How does octal permission notation calculate values?
Octal notation assigns numeric values to permissions: Read = 4, Write = 2, Execute = 1. Each digit in the 3-digit octal code represents the sum of permissions for Owner, Group, and Public/Others respectively.