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.\" Copyright (c) 1980, 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. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgment:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. 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.
.\"
.\" From: @(#)swapon.8 8.1 (Berkeley) 6/5/93
.\" $FreeBSD$
.\"
.Dd May 12, 1995
.Dt DUMPON 8
.Os
.Sh NAME
.Nm dumpon
.Nd "specify a device for crash dumps"
.Sh SYNOPSIS
.Nm
.Op Fl v
.Ar special_file
.Nm
.Op Fl v
.Ar off
.Sh DESCRIPTION
.Nm Dumpon
is used to specify a device where the kernel can save a crash dump in
the case of a panic.
.Pp
Calls to
.Nm
normally occur from the system multi-user initialization file
.Pa /etc/rc ,
controlled by the
.Dq dumpdev
variable in the boot time configuration file
.Pa /etc/rc.conf .
.Pp
The size of the specified dump device must be at least 64 KB greater the
size of physical memory.
.Pp
The
.Fl v
flag causes
.Nm
to be verbose about its activity.
.Sh NOTES
Since a
.Xr panic 9
condition may occur in a situation
where the kernel cannot trust its internal representation
of the state of any given filesystem,
one of the system swap devices,
and
.Em not
a device containing a filesystem,
should be used as the dump device.
.Pp
The
.Nm
program operates by setting the
.Xr sysctl 3
MIB variable
.Dq kern.dumpdev
to the device number of the designated
.Ar special_file
or to
.Dv NODEV
(meaning that no dumps are to be taken) if
.Ar special_file
is the text string:
.Dq Li off .
.Sh SEE ALSO
.Xr sysctl 3 ,
.Xr fstab 5 ,
.Xr rc.conf 5 ,
.Xr config 8 ,
.Xr init 8 ,
.Xr rc 8 ,
.Xr savecore 8 ,
.Xr swapon 8 ,
.Xr panic 9
.Sh FILES
.Bl -tag -width "/dev/{ad,da}?s?b" -compact
.It Pa /dev/{ad,da}?s?b
standard swap areas
.It Pa /etc/rc.conf
boot-time system configuration
.El
.Sh BUGS
Because the filesystem layer is already dead by the time a crash dump
is taken, it is not possible to send crash dumps directly to a file.
.Pp
Since
.Nm
can only be called after the system enters single-user mode,
it can not be used to create dumps
for system panics during kernel initialization.
.Sh HISTORY
The
.Nm
command appeared in
.Fx 2.1 .
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