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1 shutdown:
[NAME
]  shutdown - bring the system down
SYNOPSIS
       /sbin/shutdown [-t sec] [-arkhncfF] time [warning-message]
DESCRIPTION
       shutdown  brings  the  system  down  in a secure way.  All logged-in users are notified that the system is going down, and login(1) is blocked.  It is possible to shut the system down immediately or after a specified delay.   All  processes  are first  notified  that the system is going down by the signal SIGTERM.  This gives programs like vi(1) the time to save the file being edited, mail and news processing programs a chance to exit cleanly, etc.  shutdown does its job  by  signalling  the  init  process, asking it to change the runlevel.  Runlevel 0 is used to halt the system, runlevel 6 is used to reboot the system, and runlevel 1 is used to put to system into a state where administrative tasks can be performed; this is  the
       default  if  neither  the  -h  or  -r flag is given to shutdown.  To see which actions are taken on halt or reboot see the
       appropriate entries for these runlevels in the file /etc/inittab.
OPTIONS
       -a     Use /etc/shutdown.allow.
       -t sec Tell init(8) to wait sec seconds between sending processes the warning and the  kill  signal,  before  changing  to
              another runlevel.
       -k     Do not really shutdown; only send the warning messages to everybody.
       -r     Reboot after shutdown.
    &n