systemd and SysV

Systemd and SysV are both init systems used in Unix-like operating systems such as Linux.

List of distributions:

SysV:

The traditional init system used in Unix-like operating systems. It follows the System V Unix conventions.
SysV init relies on shell scripts located in specific directories (/etc/init.d/ and /etc/rc.d/) to start and stop services.
SysV init starts services sequentially, meaning that one service has to be fully started before the next one begins.
Limited parallelism in SysV init can lead to slower boot times, especially on systems with many services.
Dependency management in SysV init is often managed manually in script files, which can become complex and error-prone.

A more modern init system designed to overcome some of the limitations of SysV init.
Uses unit files (*.service, *.socket, etc.) to describe how services should be started, stopped, and managed. These unit files can include dependency information and other configurations.
Allows for parallel startup of services, improving boot times by starting services in parallel when possible.
Systemd handles dependency management automatically based on the information provided in unit files, simplifying service management.
Systemd includes features for enhanced logging (journalctl) and monitoring of system services, making it easier to troubleshoot and manage the system.
Systemd includes many other features such as socket activation, on-demand starting of services, cgroup-based process tracking, and more.