LINUX · SYSTEMS · SECURITY
Linux
under the hood.
Administration, hardening, command-line diagnostics, services and troubleshooting for real-world systems.
01
Administration
Users, permissions, processes, storage, networking and services.
02
Hardening
Reduce attack surface with secure configuration and least privilege.
03
Diagnostics
Use logs, processes, sockets and system state to isolate root causes.
04
Automation
Make repeatable administration safer with scripts and controlled workflows.
Diagnostic model
Start with symptoms, establish current system state, inspect the relevant subsystem and validate the smallest change that resolves the issue.
Observe → Reproduce → Inspect → Change → Verify
Useful first checks
systemctl --failed
journalctl -p warning..alert -b
ss -tulpn
free -h
df -h
Commands are starting points, not conclusions. Correlate their output with timestamps, recent changes and application logs before deciding on remediation.