Chmod Calculator

How Linux file permissions work

Every file and directory on Linux has three permission groups: Owner, Group, and Public (others). Each group can have read (r), write (w), and execute (x) permissions.

Understanding octal notation

Each permission has a numeric value: read = 4, write = 2, execute = 1. Add them together for each group:

So chmod 755 means: owner can read+write+execute (7), group and public can read+execute (5).

Common chmod values

• 755 — Directories and executables. Owner has full control, others can read and traverse.
• 644 — Regular files. Owner can edit, others can only read.
• 600 — Private files like SSH keys or .env files. Only the owner can access.
• 700 — Private directories. Only the owner can enter or list contents.
• 777 — Full access for everyone. Avoid this on production servers.

chmod on a real server

When you deploy to a server, getting permissions right matters. Wrong permissions on SSH keys block login. Wrong permissions on web files block your site.