Copyright (c) 1990, 1991, 1993
The Regents of the University of California. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. Neither the name of the University nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
@(#)reboot.8 8.1 (Berkeley) 6/9/93
.Dd September 12, 2016 .Dt REBOOT 8 .Os .Sh NAME .Nm reboot , .Nm poweroff , .Nm halt .Nd restarting, powering down and stopping the system .Sh SYNOPSIS .Nm halt .Op Fl dlnpqvxz .Nm poweroff .Op Fl dlnqvxz .Nm .Op Fl dlnqvxz .Op Ar arg ... .Sh DESCRIPTION The .Nm poweroff , .Nm halt and .Nm utilities flush the file system cache to disk, send all running processes a .Dv SIGTERM , wait for up to 30 seconds for them to die, send a .Dv SIGKILL to the survivors and, respectively, power down, halt or restart the system. The action is logged, including entering a shutdown record into the login accounting file and sending a message via .Xr syslog 3 .
p The options are as follows: l -tag -width Ds t Fl d Create a dump before halting or restarting. This option is useful for debugging system dump procedures or capturing the state of a corrupted or misbehaving system. t Fl l Suppress sending a message via .Xr syslog 3 before halting or restarting. t Fl n Do not flush the file system cache. This option should be used with extreme caution. It can be used if a disk or a processor is on fire. t Fl p Attempt to powerdown the system. If the powerdown fails, or the system does not support software powerdown, the system will halt. This option is only valid for .Nm halt . t Fl v To enable verbose messages on the console, pass the .Xr boothowto 9 flag .Dv AB_VERBOSE to .Xr reboot 2 . t Fl x To enable debugging messages on the console, pass the .Xr boothowto 9 flag .Dv AB_DEBUG to .Xr reboot 2 . t Fl z To silence some shutdown messages on the console, pass the .Xr boothowto 9 flag .Dv AB_SILENT to .Xr reboot 2 . t Fl q Do not give processes a chance to shut down before halting or restarting. This option should not normally be used. .El
p If there are any arguments passed to .Nm reboot they are concatenated with spaces and passed as .Fa bootstr to the .Xr reboot 2 system call. The string is passed to the firmware on platforms that support it.
p 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. .Sh SEE ALSO .Xr reboot 2 , .Xr syslog 3 , .Xr utmp 5 , .Xr boot 8 , .Xr init 8 , .Xr rescue 8 , .Xr shutdown 8 , .Xr sync 8 .Sh HISTORY A .Nm command appeared in x 4.0 .
p The .Nm poweroff command first appeared in .Nx 1.5 . .Sh CAVEATS Once the command has begun its work, stopping it before it completes will probably result in a system so crippled it must be physically reset. To prevent premature termination, the command blocks many signals early in its execution. However, nothing can defend against deliberate attempts to evade this.
p This command will stop the system without running any .Xr shutdown 8 scripts. Amongst other things, this means that swapping will not be disabled so that .Xr raid 4 can shutdown cleanly. You should normally use .Xr shutdown 8 unless you are running in single user mode. .Sh BUGS The single user shell will ignore the .Dv SIGTERM signal. To avoid waiting for the timeout when rebooting or halting from the single user shell, you have to c exec reboot or c exec halt .
Indexes created Sun Sep 21 16:09:51 GMT 2025