Maintenance shutdown, reboot, and halt (power down)

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.

• Reboot immediately, kill all running processes 10 seconds after sending process warning signals:

  /sbin/shutdown -r -t10 now

• Halt (power down) a system in 3 minutes seconds and show shutdown messages:

  /sbin/shutdown -h -t10 +3 "==System power down=="

• Shutdown for maintenance (single user mode):

  /sbin/telinit 1

When shutdown command is issued, no one is allowed to login except root.