Journalctl

Executive Summary Linux boot is a multi-stage handoff: UEFI → Bootloader → Kernel → systemd → Targets → Units. Each stage has failure points. This guide shows the sequence, where failures occur, and how to capture logs. Why understanding boot flow matters: When a Linux server won’t boot, you need to know WHICH stage failed to fix it effectively. A black screen could mean anything from bad hardware to a typo in /etc/fstab. …

Executive Summary Observability = see inside your systems: metrics (CPU, memory, I/O), logs (audit trail), traces (syscalls, latency). This guide covers: Metrics: node_exporter → Prometheus (system-level health) Logs: journald → rsyslog/Vector/Fluent Bit (aggregation) eBPF tools: 5 quick wins (trace syscalls, network, I/O) Triage: 5-minute flowchart to diagnose CPU, memory, I/O, network issues 1. Metrics: node_exporter & Prometheus What It Is node_exporter: Exposes OS metrics (CPU, memory, disk, network) as Prometheus scrape target Prometheus: Time-series database; collects metrics, queries, alerts Dashboard: Grafana visualizes Prometheus data Install node_exporter Ubuntu/Debian: …

Executive Summary Reliability means predictable, auditable behavior. This guide covers: Time sync: Chrony for clock accuracy (critical for logging, security) Networking: Stable interface names & hostnames (infrastructure consistency) Logging: Persistent journald + logrotate (audit trail + disk management) Shutdown: Clean hooks to prevent data loss Patching: Kernel updates with livepatch (zero-downtime), tested rollback 1. Time Synchronization (chrony) Why Time Matters Critical for: Logging: Accurate timestamps for debugging, compliance audits Security: TLS cert validation, Kerberos, API token expiry Distributed systems: Causality ordering (happens-before relationships) Monitoring: Alert timing, metric correlation Cost of poor time sync: …