Linux

Overview The process scheduler is a core component of the operating system kernel — it determines which process runs on which CPU and for how long. Linux has used CFS (Completely Fair Scheduler) as its default scheduler since 2.6.23, and after years of evolution, introduced EEVDF (Earliest Eligible Virtual Deadline First) to replace CFS in the 6.6 kernel. This article provides an in-depth analysis of CFS principles, nice/cgroup CPU control, real-time scheduling, CPU affinity, and other core topics, with production tuning experience....

Overview Memory is one of the most precious resources in a Linux system. Understanding how the kernel manages memory not only helps you troubleshoot OOM and memory leak issues in production, but also enables better decisions in capacity planning and performance tuning. This article starts from the virtual memory model and covers core topics including Page Cache, Swap policies, OOM Killer principles, cgroup v2 memory limits, slab/shmem tuning, with multiple production case studies....

Overview The Linux boot process is a precisely orchestrated multi-stage sequence — from firmware power-on self-test to kernel loading, all the way to userspace service startup. Each stage has its specific responsibilities. Understanding the complete boot process not only helps troubleshoot boot failures but also enables boot performance optimization. This article proceeds layer by layer from the firmware level through BIOS/UEFI, GRUB2, initramfs, kernel initialization, and systemd startup, covering boot optimization and kernel crash recovery....

Overview Package management is foundational to Linux system administration. Debian-based systems use apt/dpkg, while Red Hat-based systems use yum/dnf/rpm. Understanding both package management ecosystems — their principles and usage — along with repository management, dependency resolution, package building, version pinning, and offline installation, is a prerequisite for efficient operations. This article systematically compares the two ecosystems and dives into practical package building and mirror optimization. apt/dpkg Ecosystem Architecture apt (high-level frontend) │ ├── apt-get → package install/remove/update ├── apt-cache → package query/search └── apt → unified command (user-friendly) │ dpkg (low-level tool) │ ├── dpkg → ....

Introduction Disk I/O is often the slowest link in the system performance chain. A single mechanical disk seek takes about 10ms, while memory access takes only about 100ns — a 100,000x difference. When business applications experience latency jitter or slow response times, the investigation inevitably points to the I/O subsystem. This article starts from the metrics system, combined with hands-on tool usage and production case studies, to build a reusable I/O diagnosis methodology....

Overview Scheduled tasks are a foundational component of operations automation — log rotation, data backups, certificate renewal, health checks, report generation — nearly every ops scenario relies on scheduled execution. Most people’s understanding of scheduled tasks stops at crontab -e plus a line like 0 2 * * * /path/to/script.sh, but this is far from sufficient in production: who gets notified when a task fails? Who handles execution timeouts? How do you coordinate tasks across multiple machines?...

Overview Logs are the eyes of system operations. From kernel messages to application logs, from security auditing to performance analysis, logs run through every aspect of troubleshooting. Modern Linux uses journald as the system logging daemon, combined with logrotate for log rotation, forming a complete log management infrastructure. This article dives deep into journald internals and configuration, advanced journalctl query techniques, log rotation strategies, remote log collection solutions, and practical analysis cases....

systemd Architecture Overview systemd is the de facto standard init system for modern Linux distributions, having replaced SysVinit as the default init in most mainstream distributions since 2015. It is not merely a “service starter” but a complete system and service manager. Core Unit Types systemd manages system resources through units, with each unit type corresponding to a specific resource type: Unit Type Extension Purpose service .service System services (daemons) socket ....

Overview Performance profiling is a core SRE skill. Linux provides a rich set of performance analysis tools, from the simple top to the powerful perf/eBPF — each with its applicable scenario. Knowing when and how to use these tools is key to quickly identifying performance bottlenecks. This article systematically covers the Linux performance profiling toolkit across five dimensions — CPU, memory, IO, network, and comprehensive tools — and provides use-case quick reference tables and real-world examples....

Introduction Shell scripts are the most common automation tool for operations engineers. This post records several practical patterns used in the field. Log Rotation Cleanup #!/bin/bash # clean_logs.sh - Log cleanup script LOG_DIR="/var/log/app" KEEP_DAYS=30 find "$LOG_DIR" -name "*.log" -type f -mtime +${KEEP_DAYS} -exec gzip {} \; find "$LOG_DIR" -name "*.gz" -type f -mtime +${KEEP_DAYS} -delete echo "$(date): Log cleanup complete, kept ${KEEP_DAYS} days" Run daily via crontab: 0 2 * * * /opt/scripts/clean_logs....