Sysvinit Runlevels
Sysvinit runlevels are a concept from the System V init system, a traditional Unix/Linux initialization system that defines operational states or modes for a system. Each runlevel (numbered 0-6) specifies a set of services and processes to start or stop, controlling the system's behavior, such as single-user mode, multi-user with networking, or shutdown. This system was widely used in older Linux distributions to manage boot sequences and system states.
Developers should learn Sysvinit runlevels when working with legacy Linux systems, embedded devices, or maintaining older infrastructure, as it helps understand boot processes and service management in those environments. It's useful for troubleshooting startup issues, configuring system states, and writing scripts that depend on specific runlevels, though modern systems often use alternatives like systemd.