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REBOOT(8)                 BSD System Manager's Manual                REBOOT(8)

NAME
     halt, reboot -- stopping and restarting the system

SYNOPSIS
     halt [-lnqu]
     reboot [-lnq]

DESCRIPTION
     The halt and reboot utilities flush the file system cache to disk, send all running processes a SIGTERM
     (and subsequently a SIGKILL) and, respectively, halt or restart the system.  The action is logged,
     including entering a shutdown record into the wtmp(5) file.

     When the system is halted with the halt command, the system is powered off.

     The options are as follows:

     -l      The halt or reboot is not recorded in the system log.  This option is intended for applications
             such as shutdown(8), that call reboot or halt and log this themselves.

     -n      The file system cache is not flushed.  This option should probably not be used.

     -q      The system is halted or restarted quickly and ungracefully, and only the flushing of the file
             system cache is performed (if the -n option is not specified).  This option should probably not
             be used.

     -u      The system is halted up until the point of removing system power, but waits before removing
             power for 5 minutes so that an external UPS (uninterruptible power supply) can forcibly remove
             power.  This simulates a dirty shutdown to permit a later automatic power on. OS X uses this
             mode automatically with supported UPSs in emergency shutdowns.

     Normally, the shutdown(8) utility is used when the system needs to be halted or restarted, giving users
     advance warning of their impending doom and cleanly terminating specific programs.

SIGTERM TO SIGKILL INTERVAL
     The SIGKILL will follow the SIGTERM by an intentionally indeterminate period of time.  Programs are
     expected to take only enough time to flush all dirty data and exit.  Developers are encouraged to file
     a bug with the OS vendor, should they encounter an issue with this functionality.

SEE ALSO
     wtmp(5), shutdown(8), sync(8)

HISTORY
     A reboot utility appeared in Version 6 AT&T UNIX.

BSD                              June 9, 1993                              BSD