问一个很简单的问题

朽木可雕

The shutdown Command Details
Executing the shutdown command stops system activities in an orderly and consistent
manner. The shutdown command performs the following tasks:
• Prompts the administrator for a broadcast message to send to all users.
• Broadcasts the warning message to all user terminal sessions.
• Grants a 60 second (by default) grace period for users to log out.
• Kills all user logins.
• Shuts down all non-critical processes.
• Unmounts all non-critical file systems.
Depending on the option specified, shutdown will either leave the system in single-user mode
(no options), the halt state (if -h was specified), or initiate a reboot (if -r was specified).
Common shutdown options:
# shutdown -hy 600 # shutdown to a halt state in 600 seconds.
# "-y" (yes) option prevents shutdown from
# requesting confirmation before proceeding.
# shutdown -ry 600 # reboot in 600 seconds without requesting confirmation.
# shutdown -ry 0 # reboot immediately without requesting confirmation.

Reboot Command Details
The reboot command uses "kill -9" to kill running processes,
quickly, but can cause problems for applications and file
shuts down applications and processes more gracefully,
halting or rebooting the system from multi-user mode.
The system is already in single-user mode.
You need to bring the system down very quickly.