What Is systemd and Why Do So Many Linux Distros Use It?
Learn what systemd is, how it became the default init system for most Linux distributions, and how to manage services with basic systemctl commands.
Publish date: 12/1/2025
Learn what systemd is, how it became the default init system for most Linux distributions, and how to manage services with basic systemctl commands.
Publish date: 12/1/2025
If you've managed any modern Linux server, you've definitely interacted with systemd, even if you didn't realize it. When your server boots up, systemd is the very first process that starts (it always has Process ID 1, or PID 1) and it's responsible for, well, starting everything else.
It's the standard init system for almost all major distributions, including Debian, Ubuntu, and RHEL. But it's also one of the most debated pieces of software in the Linux community.
So, what is it, why did it take over, and how do you use it?
At its heart, systemd is an init system and service manager.
To understand why that matters, let's look at the "old way." For decades, Linux used a system called SysVinit (System V init). When the kernel finished loading, it would start a single program called init. This init program would then read a series of shell scripts, usually stored in /etc/init.d/, to start services like your web server, database, and SSH daemon.
The problem? It was mostly sequential. It ran script A, waited for it to finish, ran script B, waited, and so on. This made boot times slow and managing service dependencies (like "don't start the web server until the database is running") a complex mess of scripting.
systemd was created to fix this. It takes a different approach, starting services in parallel whenever possible. It manages "units" instead of just scripts, allowing it to understand the dependencies between services, hardware, and filesystem mounts. This parallelization and dependency management leads to a much faster and more organized boot process.
systemd isn't just one program; it's a suite of tools for managing a Linux system. While there are many components, there are three you'll encounter most often.
nginx.service or multi-user.target) describe what to do, not how to do it. This makes them easier to write and maintain. This system also includes .timer units, which are a modern replacement for the traditional cron. If you're deciding between the two, it's helpful to understand systemd vs. cron for task scheduling.journalctl command to query these logs in great detail, which is much simpler than hunting through multiple files in /var/log/.For most day-to-day server administration, you'll just need a few systemctl commands. Let's use nginx as an example service.
To check the status of a service:
This command tells you if the service is running, if it's enabled to start on boot, and shows the most recent log entries.
systemctl status nginx.service
To start or stop a service:
These commands start or stop the service immediately.
systemctl start nginx.service
systemctl stop nginx.service
To restart or reload a service:
Restart will stop and then start the service. Reload is better, as it tells the service to just reload its configuration file without dropping connections.
systemctl restart nginx.service
systemctl reload nginx.service
To enable or disable a service on boot:
Enable creates a link so the service starts automatically when the server boots. Disable removes that link.
systemctl enable nginx.service
systemctl disable nginx.service
And if something goes wrong, you can check the specific logs for that service using journalctl:
journalctl -u nginx.service
You can't talk about systemd without mentioning the controversy. It's a heated topic for many system administrators.
Supporters point out that systemd provides a standardized, centralized, and efficient way to manage a modern server. Its dependency handling is smart, it speeds up boot times, and systemctl is arguably much easier to use than the old init.d scripts.
Critics argue that systemd violates the classic "Unix philosophy," which states that a program should do one thing and do it well. systemd is not just an init system; it also handles logging, device management, user sessions, and networking. Critics see this as a complex, monolithic design that's harder to debug and audit.
Regardless of which side you're on, systemd is the standard on most Linux systems today. Understanding how it works and how to use systemctl is a fundamental skill for any Linux developer or sysadmin.
PID 1 (Process ID 1) is the first process started by the Linux kernel at boot. This process is the "ancestor" of all other processes and is responsible for starting and managing all other services on the system. If PID 1 dies, the entire system stops.
The main difference is how they start services. SysVinit uses sequential shell scripts, which is slow. systemd uses declarative "unit files" and starts services in parallel, which is much faster and allows for better dependency management.
A unit file is a simple text file that tells systemd what a service, device, or target is and how to manage it. For example, a .service file specifies the command to run, the user to run it as, and what other services it depends on.
Yes, but it's not easy on mainstream distributions. There are "init-free" distros like Devuan (a fork of Debian) or Artix Linux (a fork of Arch) that don't use systemd. It's also possible to replace systemd on some distros, but it's an advanced task that's generally not recommended for production servers.
For better or worse, systemd is a central part of modern Linux administration. It streamlines how services are managed, logged, and started, and knowing how to use systemctl is essential for anyone running a Linux server.
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