Five layers. Five things to remember. If everything else fades, keep these.
LINUX
│
┌───────────┼───────────┐
↓ ↓ ↓
Filesystem Processes Networking
│ │ │
pwd/ls/cd ps/top/kill ping/curl/ssh
│
↓
Permissions
│
chmod/chown
│
↓
Shell
│
| > >> sudo
The five things #
1. Linux is filesystem-oriented #
Everything starts from /, and paths tell you exactly where things live.
2. pwd, ls, cd are your foundation #
Where am I? What’s here? Take me somewhere else. That’s 80% of navigation.
3. Permissions control access #
read, write, execute — expressed as letters or as numbers (755 = rwxr-xr-x, 644 = rw-r--r--).
4. Processes have PIDs #
ps asks what’s running, top shows it live, kill stops it.
5. Commands become powerful when combined #
ps aux | grep nginx, tail -f application.log, grep ERROR application.log > errors.txt — the real leverage in Linux is chaining small, simple tools together.
This is the minimum foundation before moving into services, systemd, shell scripting, Docker, Kubernetes, CI/CD, and cloud administration.
