Chmod Permissions Calculator
Managing Linux server file permissions via the command line can be error-prone if you don't perfectly memorize the Read (4) + Write (2) + Execute (1) octal mathematics. The Chmod Calculator is an interactive, visual utility for sysadmins and developers to safely construct permissions. Check the boxes corresponding to what the Owner, Group, and Public users should be allowed to do, and grab the exact `chmod` terminal command instantly.
100% Private & Secure
This tool runs completely inside your browser using client-side WebAssembly and JS. Zero data is ever sent to our servers.
Owner
Group
Public
How to use this tool
- Select the 'Read', 'Write', or 'Execute' checkboxes under the 'Owner' column to set the file owner's permissions.
- Repeat the process for the 'Group' (users in the same system group) and 'Public' (everyone else on the system).
- The tool will instantly calculate the 3-digit Octal Notation (e.g., 755).
- It will also generate the Symbolic Notation (e.g., -rwxr-xr-x) which is what you see when you run `ls -la` in the terminal.
- Click the 'Copy' button on the Linux Command bar to quickly run the modification on your server.
Example Usage
Standard Web Server Directory (Owner: All, Group/Public: Read/Execute)
chmod 755 /var/www/html Symbolic: -rwxr-xr-x
Private SSH Key (Owner: Read/Write, Group/Public: Nothing)
chmod 600 ~/.ssh/id_rsa Symbolic: -rw-------
When to use this tool
- Securing SSH keys by deploying the strict `600` integer permission to prevent critical warning errors from the ssh daemon.
- Configuring web application directories correctly (`755` for folders, `644` for flat files) to prevent unauthorized hacking access.
- Making a standalone shell script executable (`chmod 744 script.sh`) so the owner can run it from the command line.
Frequently Asked Questions
How is the Octal number calculated mathematically?
It is a simple addition of powers of 2 for each permission tier. Read = 4, Write = 2, Execute = 1. If an Owner has Read and Execute, you add 4 + 1 to get '5' for the first digit. A full 7 means `4 + 2 + 1` (All permissions).
What does the 777 permission mean?
`777` grants complete Read, Write, and Execute control to every single user on the server system. It is notoriously dangerous and is highly discouraged in production environments, as any compromised user can alter or delete the file.
What is the difference between chmod and chown?
`chmod` (Change Mode) alters *what* actions can be performed on a file (reading, writing, executing). `chown` (Change Owner) alters *who* internally owns the file. Modifying chmod rules without holding ownership requires `sudo` privileges.
Can I type the Octal number directly?
Yes, our interactive tool runs in both directions! If you paste '644' directly into the Octal Notation input box, the checkboxes above will instantly update to visually reflect those permissions.