chmod Calculator (Linux File Permissions)
Tick the boxes or type a number like 755 and see what it means, the rwx version and the exact chmod command. It warns you about risky settings like 777 and badly protected SSH keys.
🔒 Runs entirely in your browser. Nothing you type is sent anywhere.
How to use it
- Type a number such as
755or0640, or tick the boxes for owner, group and others. - Read what each group of users can do, and the matching
rwxstring you’d see inls -l. - Add the file name (optional) and copy the
chmodcommand.
How the numbers work
Each digit is the sum of three permissions: read = 4, write = 2, execute = 1. The three digits are, in order, the owner, the file’s group, and everyone else.
So 754 means owner 7 (4+2+1, read, write and execute), group 5 (4+1, read and execute) and others 4 (read only). An optional fourth digit at the front sets the special bits: setuid = 4, setgid = 2, sticky = 1.
Safe defaults worth remembering
| Permissions | rwx | Use it for |
|---|---|---|
| 644 | rw-r--r-- | Normal files, web pages, config that others may read |
| 640 | rw-r----- | Config with secrets that a service group needs to read |
| 600 | rw------- | SSH private keys, .env files, anything secret |
| 755 | rwxr-xr-x | Scripts and programs, and normal folders |
| 750 | rwxr-x--- | Folders only the owner and a group should enter |
| 700 | rwx------ | Your ~/.ssh folder and other private folders |
| 1777 | rwxrwxrwt | Shared temp folders like /tmp (sticky bit set) |
FAQ
Why is 777 a bad idea? It lets every user and every process on the system change or replace the file. On a web server that’s an easy way in for an attacker. If something “only works with 777”, the real fix is usually the owner or group: see our chown and chmod guide.
What does execute mean on a folder? For folders, execute means “can enter and access things inside”. That’s why folders are usually 755 or 700, not 644.
Why does SSH say my key permissions are too open?
SSH refuses private keys that group or others can read. Run chmod 600 ~/.ssh/id_ed25519 (or your key’s name) and chmod 700 ~/.ssh.
Is anything sent to a server? No. It all runs in your browser.