Chmod Calculator
Convert Linux file permissions between checkboxes, octal and symbolic notation — and copy the exact chmod command.
| Class | Read (4) | Write (2) | Execute (1) | Octal |
|---|---|---|---|---|
| Owner (u) | 7 | |||
| Group (g) | 5 | |||
| Others (o) | 5 |
chmod 755 filename
How chmod Permissions Work
View file content or list directory names.
Modify files or add/delete directory files.
Run programs or traverse into directories.
Linux calculates permissions for three user classes: the file Owner (u), the assigned Group (g), and Others (o). Each digit in a 3-digit chmod command is simply the sum of the desired rights for that class. For example, granting full access (Read 4 + Write 2 + Execute 1) equals 7. Granting Read (4) and Execute (1) equals 5. Combining these produces the universal standard chmod 755.
Most Common chmod Permissions
Frequently used file and directory modes in Linux systems administration:
Recommended Permissions Cheat Sheet
Quick reference guide for securing standard web assets, credentials, and server files:
| Use Case | Mode | Symbolic | Command |
|---|---|---|---|
| Web directories | 755 |
rwxr-xr-x |
chmod 755 /var/www/html |
| Web files (HTML, CSS, PHP) | 644 |
rw-r--r-- |
chmod 644 index.html |
| Executable scripts | 755 |
rwxr-xr-x |
chmod 755 deploy.sh |
| SSH private key (~/.ssh/id_ed25519) | 600 |
rw------- |
chmod 600 ~/.ssh/id_ed25519 |
| ~/.ssh directory | 700 |
rwx------ |
chmod 700 ~/.ssh |
| authorized_keys | 600 |
rw------- |
chmod 600 ~/.ssh/authorized_keys |
| AWS .pem key | 400 |
r-------- |
chmod 400 key.pem |
| /etc/sudoers | 440 |
r--r----- |
chmod 440 /etc/sudoers |
| Shared group project directory | 2775 |
rwxrwsr-x |
chmod 2775 /var/project |
| /tmp-style shared directory | 1777 |
rwxrwxrwt |
chmod 1777 /tmp |
| wp-config.php | 440 |
r--r----- |
chmod 440 wp-config.php |
| .env files | 600 |
rw------- |
chmod 600 .env |
Special Permissions (setuid, setgid, sticky bit)
Linux supports an optional leading fourth digit for advanced security policies, including process privilege elevation and collaborative group directory inheritance:
Linux Permission Guides
Comprehensive tutorials explaining Unix security fundamentals and best practices:
Popular Comparisons
Compare frequently confused file permissions side by side:
Frequently Asked Questions
What does chmod 755 mean?
chmod 755 grants read, write, and execute permissions (7) to the file owner, and read plus execute permissions (5) to group members and all other users. It is the international standard configuration for Linux directories, web roots, and executable programs.
What is the difference between chmod 644 and 755?
chmod 644 provides read and write permissions to the owner, and read-only access to others, omitting the execute bit entirely. chmod 755 includes the execute bit for all classes. Regular files (HTML, CSS, images) should use 644, while directories and executable scripts require 755.
Is chmod 777 safe?
No. chmod 777 grants full read, write, and execute access to every user and process on the entire operating system. It allows unprivileged local users or compromised scripts to overwrite or delete files, and should never be used on production servers.
How do I calculate chmod numbers?
Each permission right has an octal value: Read = 4, Write = 2, and Execute = 1. To determine the digit for a user class, add their rights together (e.g., Read + Write = 4 + 2 = 6). Repeating this for owner, group, and others creates a 3-digit mode like 755 or 644.
What does the first digit mean in a 4-digit chmod like 4755?
The leading digit in a 4-digit chmod command represents special permissions: 4 designates setuid (runs with owner privileges), 2 represents setgid (inherits group ownership on directories), and 1 enables the sticky bit (restricts deletion in shared folders like /tmp).