How a system gets the default runlevel?

A system determines its default runlevel through the configuration files typically located in /etc/inittab or, in newer systems using systemd, through the default target specified in the /etc/systemd/system/default.target file. The default runlevel or target indicates the state in which the system will start, such as multi-user mode or graphical mode. During the boot process, the init system reads this configuration to establish the appropriate environment and services to launch. If not explicitly set, the system may fall back to a predefined runlevel or target.