How to dynamically change the runlevel of Linux system without rebooting

The current run level of the system can be changed dynamically without the necessity to reboot the system. This can be achieved using the telinit command with the required runlevel as the command line argument.
For example you can switch into single user mode by running the following command:
    telinit S
The administrator could subsequently return to full multi-user, X graphical interface mode either by entering:
    telinit 5

If you have made changes to the /etc/inittab file to change the default runlevel and want to change the system to that new default you can do so by using the telinit with the q command-line option:
    telinit q

It is important to note that telinit can only be run as root and even then only from the system console.