Description: The ‘runlevel’ refers to an init state in which a specific set of processes is running in an operating system. This concept is fundamental in system management, as it determines which services and applications are active at any given time. In Unix and Linux-based systems, the runlevel is commonly associated with different runlevels or targets, which are predefined configurations that control the system’s state. For example, a system may be in a runlevel that allows full access to a graphical interface, while another may be configured to operate in text mode, limiting access to certain services. The transition between these runlevels is managed through startup scripts that run at system boot, allowing administrators to customize the execution environment according to specific needs. This flexibility is one of the most valued features in modern operating systems, where administrators can define which processes should start automatically and which should remain inactive, thus optimizing system performance and security.
History: The concept of runlevels originated in Unix systems in the 1970s, where runlevels were introduced as a way to manage the system’s state. Over time, this concept was adopted in various Linux distributions, each implementing its own interpretation and management of runlevels. In particular, the traditional init system used runlevels from 0 to 6, where each number represented a specific system state. However, with the arrival of systemd in 2010, the approach changed, introducing a system of targets that replaced traditional runlevels, allowing for more flexible and efficient management of services.
Uses: Runlevels are primarily used to manage the state of an operating system, allowing administrators to define which services and processes should be active in different situations. This is especially useful in server environments, where specific runlevels can be configured for maintenance operations, recovery from failures, or booting in safe mode. Additionally, runlevels allow users to customize their usage experience by choosing between different configurations based on their needs.
Examples: A practical example of runlevels can be seen in a typical server installation, where certain runlevels provide access to command line interfaces without graphical environments, while others allow full access to graphical interfaces. In systems using systemd, targets like ‘multi-user.target’ and ‘graphical.target’ serve similar functions, allowing administrators to manage services more efficiently.
