Operations, Security, and Recovery

Use top and htop to inspect CPU and memory usage, sort active processes, and stop a disposable practice load.

Use journalctl to view recent logs, filter by service and time, and run one non-interactive error query.

Use UFW to inspect firewall state, allow required access, and apply simple rules without locking yourself out.

Inspect iptables rules, understand chain order, and practice one small temporary rule change with a clear rollback.

Use this when backup or restore work fails and you need to separate source, destination, permissions, schedule, and verification problems.

Use this when a service fails to start, immediately stops, or restarts into failure.

Use this when updates fail or remain stuck, and you need to inspect space, package state, services, and recovery options in a controlled order.

See boot as a staged timeline so startup, services, login, and failure points become easier to reason about.

Understand when to inspect, restore, repair, or roll back instead of jumping straight to the biggest recovery action.