Init System

In Unix-like Operating systems, including Linux, an Init system is required to enable optimal use of a OS.

Init systems, also referred to as "Initialization Systems," are a key component in the booting phase of an OS as their main task is to initialize other required processes and services to grant a functional and optimal OS. After booting up, Init systems begin to work in the background as a daemon process, their main tasks shifts from initializing components to becoming a direct or indirect ancestor of any other processes that may spawn in under the current working environment; adding on, these systems typically adopt all orphaned processes and can terminate any and all zombie processes. Seeing that their role in a operating system is to maintain functionality throughout the system, in a Unix-like Operating system, a kernel is required to have a functional and usable Init system, a kernel panic will occur if—for whatever reason—a kernel is unable to find, start, or maintain the OS's Init.

There are 2 different types of Inits,which, depending on the functionality, determines if it should be consider a Traditional Init System (TIS) or a Modern Init System (MIS). Although the end goal of both types remains consistent between the two, TIS and MIS approach each task differently and support different use cases for different hardware, with both still being used till this day.

Traditional Init Systems

Before the emergence of modern alternatives, traditional Init systems ruled in terms of any sort of initializing service and/or process, but that doesn't mean they were relatively up to today's standards. These systems relied on much slower and resource consuming processes that would be proven inefficient when release of more modernized Init systems, categorized as MIS; moreover, these systems specifically used more rigid methods to initialize services and other process in addition to their ancestry job.

Key Characteristics

1. Sequential Startup: When computer machines were much simpler, this was no problem; computers were designed for simpler operations and tasks. This was proved inefficient to computers as they began to modernize throughout the years. This type of startup began processes and services one after another, in a linear fashion. It should be taken into consideration that this isn't a disadvantage for computers today. Network configurations require a Sequential Startup to ensure all components are working; starting a service that depended on an important service before it starts the important one may cause bottlenecks and issues. But the moral of the story is that these types of start ups take crucial resources and take an excessive amount of time to boot up, their inefficient use of resources inevitably were the reason many operating systems rely on a more modernized alternative.
2. Shell Scripts: As aforementioned, the use of Shell Scripts did, in fact, have a good use as it was considered a great way to perform tasks; unfortunately, this doesn't outweigh the cons of using such a vulnerable script language. Rather than being compiled, Shell is parsed, interpreted, then executed, making inefficient use of already sparse system resources. There are many more complex issues such as, but not limited to error handling, difficult dependency management, and so forth. These types on scripts lack parallelism, discouraging running 2 scripts at once, slowing down boot processes and overall services.

Table of TIS and older.

Init Name	Production date	Last Stable Release	Discontinued	Architecture (Supported/Developed For)	(Original) Developers(s)	Devices Supported
SYSTEM III UNIX	June, 1980	~1983	Y	PDP-11, VAX	AT&T USG	Intel-8086-Based PCs, Zilog-8000-Based PCs.
Research Unix	November 3rd 1971	October, 1989	Y	PDP-7 & 11, VAX, Intel x86, Motorola 68000, SPARC	Bell Labs CRSC	DEC PDP-7, PDP-11, VAX, Interdata 7/32 & 8/32 Computers.
SYSTEM V UNIX	1983	1989	Y	DEC PDP-11, VAX, Intel x86.	AT&T Corporation	DEC VAX, DEC PDP-11, AT&T 3B2, SPARC Devices.

Modern Init Systems

As computer hardware evolved, the need for better software came along, and traditional Init systems weren't cutting the job for most people standards. Rather than continuing to use outdated and old Inits, developers at Canonical began developing a new type of Init system, nicknamed Upstart, where most, if not all problems of TIS were fixed. Instead of implementing resource inefficient task handling such as the aforementioned Sequential Startup, developers began to use more efficient method to get the same results of a TIS, but much faster, reliable, and safer.

Key Characteristics

1. Parallel Process Startup: Moving from traditional Init systems, MIS were known for their speed when compared to TIS. This came from the optimization of the Init boot process. Rather than using a Linear fashioned startup process, MIS encouraged parallelism by allowing multiple services to begin at once or when needed or when triggered by an event happening. This type of start up is better for the commercial/consumer use, unlike network configurations, some services don't need to be started before others, overall preserving system resources.
2. Event-based Triggers: Being able to trigger certain processes or services on certain events used less resources overall and allowed for system to be looking for triggers rather than looping a predefined list of instructions. Additionally, this speeds up the system even more, enhancing system efficiency, reliability, and security. These types of triggers based off events can be triggered through simple things such as clicks to user logins, network configuration, system shutdowns/reboots, etc.

Table of MIS

Init Name	Production date	Last Stable Release	Architecture (Supported/Developed for)	(Original) Developers(s)	Operating Systems (Made for/Supported)
systemd	March 30th, 2010	October 8th, 2024	AMD64, ARM64, PPC64IE, MIPS, S390X, ETC.	Lennart Poettering	Arch and Arch-Based, Ubuntu and Ubuntu Based, Debian and Debian Based. FreeBSD, OpenBSD, etc.
OpenRC	April 5th, 2007	September 18th, 2024	↓	Roy Marples	↓
runit	February 10, 2004	September 29, 2024	↓	Gerrit Pape	↓
This is a WIP Table.					↓

Concluding this topic, the emergence of MIS fixed all previous issues with TIS and produced a system that is much more efficient and reliable when compared to TIS.