Systemd

A practical guide to cgroups v2’s unified hierarchy, showing how to configure CPU, memory, and I/O limits with systemd and raw cgroup files.

cgroups v2 unifies memory, CPU, and I/O controls under a single hierarchy, simplifying container orchestration and improving predictability.

Table of Contents Introduction What Is Daemon Mode? Historical Background Key Characteristics of a Daemon Why a Session Supervisor Is Needed The Limitations of Traditional Daemons User Sessions vs. System Sessions Popular Session Supervisors systemd‑user launchd (macOS) Upstart & runit [Supervisord (Python)]#supervisord-python) Designing a Daemon for Supervision Daemonizing vs. “No‑Daemon” Approach Signal Handling & Graceful Shutdown Logging Strategies Practical Example: A Simple Go Service Managed by systemd‑user Service Code systemd Unit File Testing the Supervision Loop Advanced Topics Socket Activation Dependency Graphs & Ordering Resource Limits (cgroups, ulimits) Troubleshooting Common Pitfalls Conclusion Resources Introduction Long‑running background processes—daemons—are the invisible workhorses that keep modern operating systems functional. From web servers and database engines to personal notification agents, daemons provide services without direct user interaction. Yet writing a daemon that behaves well under every circumstance is far from trivial. Over the past two decades, the session supervisor model has emerged as a robust solution to many of the classic daemon‑related headaches. ...

Introduction When you start a computer, a flurry of processes springs to life. Some of these processes interact directly with the user—opening a terminal, rendering a graphical desktop, or launching an application. Others work silently in the background, waiting for events, handling network traffic, or performing routine maintenance. These background processes are called daemons (pronounced “dee‑mons”), and they are the invisible workhorses that keep modern operating systems reliable, responsive, and secure. ...