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After init has progressed through the run levels to get to the default run level, the /etc/inittab script forks a getty process for each virtual console (login prompt in text mode). getty opens tty lines, sets their modes, prints the login prompt, gets the user's name, and then initiates a login process for that user. This allows users to authenticate themselves to the system and use it. By default, most systems offer 6 virtual consoles, but as you can see from the inittab file, this is configurable.
/etc/inittab can also tell init how it should handle a user pressing Ctrl +Alt +Delete at the console. As the system should be properly shut down and restarted rather than immediately power-cycled, init is told to execute the command /sbin/shutdown -t3 -r now , for instance, when a user hits those keys. In addition, /etc/inittab states what init should do in case of power failures, if your system has a UPS unit attached to it.
On most RPM-based systems the graphical login screen is started in run level 5, where /etc/inittab runs a script called /etc/X11/prefdm . The prefdm script runs the preferred X display manager, based on the contents of the /etc/sysconfig/desktop directory. This is typically gdm if you run GNOME or kdm if you run KDE, but they can be mixed, and there's also the xdm that comes with a standard X installation.
But there are other possibilities as well. On Debian, for instance, There is an initscript for each of the display managers, and the content of the /etc/X11/default-display-manager is used to determine which one to start. More about the graphical interface can be read in Section 7.3 . Ultimately, your system documentation will explain the details about the higher level aspects of init .
The /etc/default and/or /etc/sysconfig directories contain entries for a range of functions and services, these are all read at boot time. The location of the directory containing system defaults might be somewhat different depending on your Linux distribution.
Besides the graphical user environment, a lot of other services may be started as well. But if all goes well, you should be looking at a login prompt or login screen when the boot process has finished.
Other procedures
We explained how SysV init works on x86 based machines. Startup procedures may vary on other architectures and distributions. Other systems may use the BSD-style init , where startup files are not split up into multiple /etc/rc<LEVEL>.d directories. It might also be possible that your system uses /etc/rc.d/init.d instead of /etc/init.d .
