Chmod Calculator & Linux Permissions Visualizer

Demystifying POSIX & Linux File Permissions

In POSIX-compliant operating systems (Linux, macOS, BSD), file access control is governed by file permission modes. The chmod (change mode) command is used by system administrators and software engineers to set read, write, and execute permissions for files and directory trees.

DevToolHub's Chmod Calculator & Visualizer translates octal numbers (`755`, `644`) into 10-character symbolic notation (`-rwxr-xr-x`) and generates terminal shell commands.

Linux Octal Bitmask Calculation

Permissions are assigned across three user classes: User (Owner), Group, and Others (World). Each class receives an octal digit calculated by summing active permission weights:

Terminal CLI Chmod & Find Workflows

Execute terminal commands to fix file and directory permissions recursively across web servers:

1. Fix Web Server Directory & File Permissions Separately

Never use `chmod -R 777`. Separate directories (755) from files (644):

# Set 755 permissions for all directories recursively
find /var/www/html -type d -exec chmod 755 {} +

# Set 644 permissions for all regular files recursively
find /var/www/html -type f -exec chmod 644 {} +

2. Secure SSH Key Pair Permissions

# Secure SSH configuration directory
chmod 700 ~/.ssh

# Restrict private keys to Owner Read/Write only
chmod 600 ~/.ssh/id_rsa ~/.ssh/id_ed25519

3. Set Special SUID / Sticky Bit Modes

# Set Sticky Bit on shared tmp directory (chmod 1777)
chmod +t /tmp/shared_uploads

# Set SGID on directory to inherit group ownership on new files
chmod g+s /var/www/shared_repo

Frequently Asked Questions