.\" Copyright (c) 1990, 1991, 1993
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.\"	@(#)reboot.8	8.1 (Berkeley) 6/9/93
.\" $FreeBSD: src/sbin/reboot/reboot.8,v 1.21 2002/12/27 12:15:33 schweikh Exp $
.\"
.Dd June 9, 1993
.Dt REBOOT 8
.Os
.Sh NAME
.Nm halt ,
.Nm reboot
.Nd stopping and restarting the system
.Sh SYNOPSIS
.Nm halt
.Op Fl lnqu
.Nm reboot
.Op Fl lnq
.Sh DESCRIPTION
The
.Nm halt
and
.Nm reboot
utilities flush the file system cache to disk,
send all running processes a
.Dv SIGTERM
(and subsequently a
.Dv SIGKILL )
and, respectively, halt or restart the system.
The action is logged, including entering a shutdown record into the
.Xr wtmp 5
file.
.Pp
When the system is halted with the halt command, the system is powered off.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl l
The halt or reboot is
.Em not
recorded in the system log.
This option is intended for applications such as
.Xr shutdown 8 ,
that call
.Nm reboot
or
.Nm halt
and log this themselves.
.It Fl n
The file system cache is not flushed.
This option should probably not be used.
.It Fl q
The system is halted or restarted quickly and ungracefully, and only
the flushing of the file system cache is performed (if the
.Fl n
option is not specified).
This option should probably not be used.
.It Fl 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.
.El
.Pp
Normally, the
.Xr 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.
.Sh SIGTERM TO SIGKILL INTERVAL
The
.Dv SIGKILL
will follow the
.Dv 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.
.Sh SEE ALSO
.Xr wtmp 5 ,
.Xr shutdown 8 ,
.Xr sync 8
.Sh HISTORY
A
.Nm reboot
utility appeared in
.At v6 .