Chmod Calculator

1. Click the permission checkboxes (Read, Write, Execute) for Owner, Group, and Others.
2. The numeric (octal) and symbolic values update instantly.
3. Alternatively, type a numeric value like 755 to set the checkboxes automatically.
4. Use the preset buttons for common permissions (644, 755, 777, etc.).
5. Copy the numeric value or the full chmod command with the Copy button.

Understanding Unix File Permissions

Unix-like systems use a permission model with three classes: Owner (the file creator), Group (users in the same group), and Others (everyone else). Each class can have Read (r), Write (w), and Execute (x) permissions. The numeric (octal) representation assigns Read = 4, Write = 2, Execute = 1, and sums them per class.

For example, 755 means the owner has full access (7 = 4+2+1), while group and others can read and execute (5 = 4+1). Directories need execute permission for users to list their contents.