Linux permissions: 640, 755 and beyond

NOVEMBER 2026 / FIELD GUIDE

Linux permissions determine which users may read, write, or execute files.

Understand the numbers

Read = 4, write = 2, execute = 1. Permissions are grouped as owner, group and others.

chmod 640 notes.txt

The owner has read/write permissions, the group has read-only access, and everyone else has none.

chmod 755 script.sh

The owner can read, write and execute. Group and others can read and execute.

Inspect permissions

ls -l notes.txt
stat notes.txt
id