After making changes to system services and runlevels, you can use the
telinit command to change runlevels on-the-fly on a running Ubuntu system. Changing runlevels this way enables system administrators to alter selected parts of a running system to make changes to the services or to put changes into effect that have already been made (such as reassignment of network addresses for a networking interface).
For example, a system administrator can quickly change the system to maintenance or single-user mode by using the
telinit command with its
S option like this:
matthew@seymour:~$ sudo telinit S
telinit command uses the init command to change runlevels and shut down currently running services.
After booting to single-user ...