Linux Permissions (chmod) Calculator
Managing file permissions in Linux shouldn't require mental math. Whether you are setting up a web server or securing a script, one wrong number can leave your system vulnerable to hackers or break your application entirely.
The Countimator chmod Calculator is a bidirectional translation engine. It bridges the gap between the visual rights (Read/Write/Execute) and the cryptic Octal numbers (e.g., 755) used in the terminal. Type a number to see what it does, or toggle the checkboxes to generate the correct command code instantly.
Two Ways to Calculate
Most tools only work one way. We built a fully reactive engine that works however you think:
1. Visual Mode (Click & Set)
Don't know the number? Just use the 3x3 Interactive Grid.
Check "Read" or "Write" for the Owner, Group, or Public.
The calculator instantly generates the Octal value (e.g., 644) and the Symbolic string (e.g., -rw-r--r--).
2. Reverse Mode (Decode)
Found a tutorial telling you to use chmod 777?
Type "777" into the input field, and the grid will light up to show you exactly what permissions you are granting.
(Spoiler: It allows everyone to delete your files!)
How Octal Permissions Work (The 4-2-1 Rule)
Linux permissions are based on binary math summed up into octal digits. Each permission type has a specific numeric value:
r (Read) = 4
w (Write) = 2
x (Execute) = 1
To get the final digit, you simply sum the values for that user group.
Example (Read + Execute): 4 + 1 = 5.
Example (Read + Write + Execute): 4 + 2 + 1 = 7.
A standard "755" permission code is just three of these sums lined up: 7 (Owner) / 5 (Group) / 5 (Public).
Common Presets & Security Standards
Not sure which code to use? Our calculator includes one-click presets for the most common server scenarios.
| Octal | Symbolic | Use Case | Safety Level |
|---|---|---|---|
| 644 | -rw-r--r-- | Standard Files. Owner can read/write; everyone else can only read. (Best for HTML/CSS). | ✅ Safe |
| 755 | -rwxr-xr-x | Directories / Scripts. Owner has full control; others can execute/access but not modify. | ✅ Safe |
| 600 | -rw------- | Private Keys (SSH). Only the owner can read or write. No one else has access. | 🔒 Secure |
| 777 | -rwxrwxrwx | The Danger Zone. Everyone can read, write, and execute. Never use this on a live server. | ❌ Unsafe |
Instant Terminal Commands
Once you have configured your permissions, the tool generates the exact command syntax you need.
Example: chmod -R 755 /var/www/html
Simply click the clipboard icon to copy it and paste it directly into your SSH terminal (PuTTY, macOS Terminal, or Linux Shell).
Frequently Asked Questions
777 gives "Write" permission to the "Public" (everyone).
This means any hacker or malicious script on your server can delete, edit, or inject malware into your files.
Always use the principle of "Least Privilege" (e.g., 644 or 755).
They represent the same thing.
Octal is the numeric representation (e.g., 755), often used because it is shorter.
Symbolic is the letter representation (e.g., rwxr-xr-x), which is what you actually see when you run `ls -l` in the terminal.
The -R flag tells the command to apply the permission to the folder and every single file and subfolder inside it.
Be careful: recursively setting 777 can compromise an entire file system in seconds.
For a file, "Execute" allows it to run as a program.
For a folder (directory), "Execute" permission is required just to enter or "cd" into that folder.
This is why folders usually need 755 (Execute allowed) while files only need 644.
Security Note: Permissions shown here are standard Linux/Unix defaults. Always verify permissions before applying them to a production server. Countimator is not responsible for security vulnerabilities caused by improper permission settings (e.g., setting public write access on sensitive directories).