Runlevels commonly follow the general patterns described in this article; however, some distributions employ certain specific configurations.
The intermediate runlevels (1–5) differ in terms of which drives are mounted and which network services are started.
Although systemd is, as of 2016[update], used by default in most major Linux distributions, runlevels can still be used through the means provided by the sysvinit project.
After the Linux kernel has booted, the /sbin/init program reads the /etc/inittab file to determine the behavior for each runlevel.
Unless the user specifies another value as a kernel boot parameter, the system will attempt to enter (start) the default runlevel.