pros, cons and features

System services in Linux provide process and service management: they start, stop and monitor the state. Recently, some of the most common and significant systems are Systemd, SysVinit, OpenRC and Upstart, which we will discuss in this article. Let's consider their features, pros and cons, and separately – the role of Systemd, which has become the de facto standard in modern Linux distributions.

Systemd

Systemd is a modern init system designed to overcome the limitations of older systems and provide more efficient and flexible service management.

How it works: Systemd uses parallel process launching, which speeds up system boot. It manages dependencies between services, ensuring that they are launched in the correct order. Systemd uses a single process (PID 1) that manages the life cycle of all other processes.

Pros:

• Powerful dependency management: Systemd allows precise control over the order in which services are started and their dependencies, which improves the stability and predictability of the system.

• Parallel launch of services: Systemd runs services in parallel, which significantly reduces system boot time.

• Extended functionality: Systemd includes many tools such as journald (logging system), systemctl (service management), timedated (time and date management), logind (user session management), and others.

• Centralized management: Systemd provides a single interface for managing services, devices, mount points, timers, and other aspects of the system, making administration easier.

Cons:

• Complexity: For many users and administrators, Systemd may seem overly complex, especially when compared to older, simpler systems.

• Not the Unix way: Systemd has been criticized for bundling together many features, which is contrary to the traditional Unix philosophy where each program does one thing and does it well.

SysVinit

SysVinit is a traditional init system used by many Linux distributions before Systemd came along.

How it works: SysVinit runs initialization scripts sequentially, in a strict order. Each runlevel has its own set of scripts that are started or stopped when switching between levels.

Pros:

• Simplicity: SysVinit is easy to learn and use, making it attractive to administrators who prefer minimalism and control over the system.

• Wide support: SysVinit has been a standard for a long time, and many scripts and tools are compatible with this initialization system.

• Transparency: All initialization scripts are easy to read and customize manually.

Cons:

• Slow Start: SysVinit starts services sequentially, which increases system boot time.

• Lack of dependency management: SysVinit does not provide built-in tools for managing dependencies between services, which can lead to problems in complex configurations.

OpenRC

OpenRC is an alternative init system that is often used in distributions that focus on flexibility and control, such as Gentoo.

How it works: OpenRC uses the concept of parallel service startup, but with stricter dependency management than SysVinit. It is compatible with SysVinit, allowing it to use existing init scripts.

Pros:

• Dependency Management: OpenRC allows better control over the order in which services are started than SysVinit, thanks to its built-in dependency management system.

• Compatibility: OpenRC is compatible with SysVinit, allowing it to be used as a replacement without requiring major changes to the system.

• Modularity: OpenRC maintains the Unix-way principle, offering modularity and flexibility in service configuration.

Cons:

• Less common: OpenRC is used primarily in specialized distributions, which limits its use and support.

• Less features than Systemd: Although OpenRC is more powerful than SysVinit, it still falls short of Systemd in functionality.

Upstart

Upstart is an init system developed by Canonical for the Ubuntu distribution, with the aim of overcoming the limitations of SysVinit.

How it works: Upstart uses events to manage the starting and stopping of services. Services can be started based on various events, such as the system booting, device connection, or the termination of other services.

Pros:

• Event-driven architecture: Upstart allows you to start and stop services based on events, making it more flexible in managing processes and services.

• Fast loading: By starting services asynchronously, Upstart can reduce system boot time.

• Compatibility: Upstart is compatible with SysVinit and can use traditional init scripts.

Cons:

• Limited support: Upstart development has been discontinued in favor of Systemd, and most Linux distributions have switched to Systemd, limiting Upstart support and development.

• Less features than Systemd: While Upstart is more flexible than SysVinit, it is inferior to Systemd in terms of functionality and dependency management.

Systemd as a de facto standard

Today, Systemd has become the de facto standard in the Linux world, adopted by most industrial and corporate distributions such as Red Hat Enterprise Linux, Ubuntu, Debian and many others.

Despite criticism for its departure from the Unix way, Systemd offers powerful tools and features that meet the requirements of modern IT infrastructures. This makes it the primary choice for most distributions, and its use has become inevitable in modern enterprise and industrial solutions.