1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" From: @(#)swapon.8 8.1 (Berkeley) 6/5/93 29.\" $FreeBSD: src/sbin/dumpon/dumpon.8,v 1.11.2.12 2003/01/26 03:12:04 keramida Exp $ 30.\" $DragonFly: src/sbin/dumpon/dumpon.8,v 1.5 2007/07/14 21:48:15 swildner Exp $ 31.\" 32.Dd May 12, 1995 33.Dt DUMPON 8 34.Os 35.Sh NAME 36.Nm dumpon 37.Nd "specify a device for crash dumps" 38.Sh SYNOPSIS 39.Nm 40.Op Fl v 41.Ar special_file 42.Nm 43.Op Fl v 44.Cm off 45.Sh DESCRIPTION 46The 47.Nm 48utility is used to specify a device where the kernel can save a crash dump in 49the case of a panic. 50.Pp 51Calls to 52.Nm 53normally occur from the system multi-user initialization file 54.Pa /etc/rc , 55controlled by the 56.Dq dumpdev 57variable in the boot time configuration file 58.Pa /etc/rc.conf . 59.Pp 60For most systems the size of the specified dump device must be at least 61the size of physical memory. 62Even though an additional header is added to the dump, 63the BIOS for a platform typically holds back some memory, so it is not usually 64necessary to size the dump device larger than the actual amount of RAM 65available in the machine. 66.Pp 67The 68.Fl v 69flag causes 70.Nm 71to be verbose about its activity. 72.Sh NOTES 73Since a 74.Xr panic 9 75condition may occur in a situation 76where the kernel cannot trust its internal representation 77of the state of any given file system, 78one of the system swap devices, 79and 80.Em not 81a device containing a file system, 82should be used as the dump device. 83.Pp 84The 85.Nm 86utility operates by setting the 87.Xr sysctl 3 88MIB variable 89.Va kern.dumpdev 90to the device number of the designated 91.Ar special_file 92or to 93.Dv NODEV 94(meaning that no dumps are to be taken) if 95.Ar special_file 96is the text string: 97.Dq Li off . 98.Pp 99Since 100.Nm 101cannot be used during kernel initialization, the 102.Va dumpdev 103variable of 104.Xr loader 8 105must be used to enable dumps for system panics which occur 106during kernel initialization. 107.Sh FILES 108.Bl -tag -width "/dev/{ad,da}?s?b" -compact 109.It Pa /dev/{ad,da}?s?b 110standard swap areas 111.It Pa /etc/rc.conf 112boot-time system configuration 113.El 114.Sh SEE ALSO 115.Xr sysctl 3 , 116.Xr fstab 5 , 117.Xr rc.conf 5 , 118.Xr config 8 , 119.Xr init 8 , 120.Xr loader 8 , 121.Xr rc 8 , 122.Xr savecore 8 , 123.Xr swapon 8 , 124.Xr panic 9 125.Sh HISTORY 126The 127.Nm 128utility appeared in 129.Fx 2.1 . 130.Sh BUGS 131Because the file system layer is already dead by the time a crash dump 132is taken, it is not possible to send crash dumps directly to a file. 133