Linux chmod File Permissions Cheat Sheet

Clear reference for Linux numeric (octal) and symbolic file permissions (rwx, 777, 755, 644, 600).

Common Numeric Permissions

Standard directories: Owner read/write/execute; Group & Others read/executechmod 755 <directory>

Standard files: Owner read/write; Group & Others read onlychmod 644 <file>

SSH Private Keys: Owner read/write only; zero access to otherschmod 600 ~/.ssh/id_rsa

SSH Directory: Owner read/write/execute onlychmod 700 ~/.ssh

Full access to Everyone: High security risk, avoid in productionchmod 777 <file>

Make shell script executable by all userschmod +x script.sh

Permission Octal Calculations

Allows viewing file contents or listing directoryRead (r) = 4

Allows modifying or deleting file contentsWrite (w) = 2

Allows running program or traversing into directoryExecute (x) = 1

Frequently Asked Questions

• Why should I never use chmod 777 in production?

chmod 777 grants read, write, and execute permissions to all users and processes on the server. If an attacker gains minimal web access, they can overwrite or execute malicious code.