Calculate Linux/Unix file permissions interactively. Toggle permissions visually and get the numeric (octal) and symbolic notation instantly.
Every file and directory in Linux has three types of permissions: read (r=4), write (w=2), and execute (x=1), applied to three categories: owner, group, and others. The chmod command uses either octal notation (e.g., 755) or symbolic notation (e.g., rwxr-xr-x) to set these permissions.
| Value | Permission | Description |
|---|---|---|
| 4 | Read (r) | View file contents / list directory |
| 2 | Write (w) | Modify file / create files in directory |
| 1 | Execute (x) | Run file / enter directory |
| 0 | None (-) | No permission |
| Octal | Symbolic | Use Case |
|---|---|---|
| 755 | rwxr-xr-x | Directories, executables |
| 644 | rw-r--r-- | Regular files |
| 600 | rw------- | Private files (SSH keys) |
| 777 | rwxrwxrwx | Full access (avoid in production!) |
| 444 | r--r--r-- | Read-only files |
chmod 777 gives full read, write, and execute permissions to everyone — including malicious users. This is a critical security risk on web servers. Files should have 644, directories 755, and sensitive files 600.
chmod changes file permissions (who can read/write/execute). chown changes file ownership (which user/group owns the file). They work together to control access.