Linux requires proper shutdown or risk filesystem crash and hence lost of precious data. Currently logged in users who are doing their critical jobs are seriously affected too. To shutdown a system properly, we need shutdown command. Sometimes when you need to carry out system maintenance without the presence of other users and user processes, you need to bring the system to a special mode - single-user mode or run-level 1. Under this mode, no normal user is allowed to login, no grahpical interface, and no network is available. The whole system is operated in a bare minimal state, so that the administrator can carry maintenance without risking the users processes and data.
/sbin/shutdown -r -t10 now
/sbin/shutdown -h -t10 +3 "==System power down=="
When shutdown command is issued, no one is allowed to login except root.