Chmod Calculator
Calculate Unix file permissions in octal and symbolic notation
Quick Presets
Permission Matrix
| Read (4) | Write (2) | Execute (1) | Value | |
|---|---|---|---|---|
| Owner (u) | 6 | |||
| Group (g) | 4 | |||
| Others (o) | 4 |
chmod 644 filenameRelated Tools
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What is Chmod and File Permissions?
Chmod (change mode) is a Unix/Linux command used to modify file and directory permissions. The permission system controls who can read, write, or execute files, providing security for multi-user systems. Understanding permissions is essential for system administrators, developers, and anyone working with Linux servers.
This interactive chmod calculator helps you understand and calculate Unix file permissions. Toggle permissions visually and see both numeric (octal) and symbolic notations instantly—no need to remember the formula!
Understanding Permission Types
Read (r) = 4
r--View file contents or list directory contents. Without read permission, you cannot open a file or see what's inside a directory.
Write (w) = 2
-w-Modify file contents or create/delete files in a directory. For directories, write permission allows creating and deleting files inside.
Execute (x) = 1
--xRun a file as a program or enter a directory. Directories need execute permission to access files inside them.
User Classes Explained
| Class | Symbol | Description |
|---|---|---|
| Owner | u | The user who owns the file (usually the creator) |
| Group | g | Users who belong to the file's assigned group |
| Others | o | Everyone else (all other users on the system) |
Common Permission Settings
644 (rw-r--r--)755 (rwxr-xr-x)600 (rw-------)777 (rwxrwxrwx)Frequently Asked Questions
Why is 777 considered dangerous?
777 gives everyone full access to read, modify, and execute files. On a server, this means any user (including attackers) can modify or run your files, creating serious security vulnerabilities.
What's the difference between numeric and symbolic notation?
Numeric (octal) uses three digits (e.g., 755). Symbolic uses letters (e.g., rwxr-xr-x). Both represent the same permissions—numeric is faster to type, symbolic is easier to read.
How do I change permissions recursively?
Use chmod -R 755 directory/ to change permissions for a directory and all its contents.
Be careful—this affects all files and subdirectories.