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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgment: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" From: @(#)swapon.8 8.1 (Berkeley) 6/5/93 33.\" $FreeBSD: src/sbin/dumpon/dumpon.8,v 1.11.2.12 2003/01/26 03:12:04 keramida Exp $ 34.\" $DragonFly: src/sbin/dumpon/dumpon.8,v 1.5 2007/07/14 21:48:15 swildner Exp $ 35.\" 36.Dd May 12, 1995 37.Dt DUMPON 8 38.Os 39.Sh NAME 40.Nm dumpon 41.Nd "specify a device for crash dumps" 42.Sh SYNOPSIS 43.Nm 44.Op Fl v 45.Ar special_file 46.Nm 47.Op Fl v 48.Cm off 49.Sh DESCRIPTION 50The 51.Nm 52utility is used to specify a device where the kernel can save a crash dump in 53the case of a panic. 54.Pp 55Calls to 56.Nm 57normally occur from the system multi-user initialization file 58.Pa /etc/rc , 59controlled by the 60.Dq dumpdev 61variable in the boot time configuration file 62.Pa /etc/rc.conf . 63.Pp 64For most systems the size of the specified dump device must be at least 65the size of physical memory. 66Even though an additional header is added to the dump, 67the BIOS for a platform typically holds back some memory, so it is not usually 68necessary to size the dump device larger than the actual amount of RAM 69available in the machine. 70.Pp 71The 72.Fl v 73flag causes 74.Nm 75to be verbose about its activity. 76.Sh NOTES 77Since a 78.Xr panic 9 79condition may occur in a situation 80where the kernel cannot trust its internal representation 81of the state of any given file system, 82one of the system swap devices, 83and 84.Em not 85a device containing a file system, 86should be used as the dump device. 87.Pp 88The 89.Nm 90utility operates by setting the 91.Xr sysctl 3 92MIB variable 93.Va kern.dumpdev 94to the device number of the designated 95.Ar special_file 96or to 97.Dv NODEV 98(meaning that no dumps are to be taken) if 99.Ar special_file 100is the text string: 101.Dq Li off . 102.Pp 103Since 104.Nm 105cannot be used during kernel initialization, the 106.Va dumpdev 107variable of 108.Xr loader 8 109must be used to enable dumps for system panics which occur 110during kernel initialization. 111.Sh FILES 112.Bl -tag -width "/dev/{ad,da}?s?b" -compact 113.It Pa /dev/{ad,da}?s?b 114standard swap areas 115.It Pa /etc/rc.conf 116boot-time system configuration 117.El 118.Sh SEE ALSO 119.Xr sysctl 3 , 120.Xr fstab 5 , 121.Xr rc.conf 5 , 122.Xr config 8 , 123.Xr init 8 , 124.Xr loader 8 , 125.Xr rc 8 , 126.Xr savecore 8 , 127.Xr swapon 8 , 128.Xr panic 9 129.Sh HISTORY 130The 131.Nm 132utility appeared in 133.Fx 2.1 . 134.Sh BUGS 135Because the file system layer is already dead by the time a crash dump 136is taken, it is not possible to send crash dumps directly to a file. 137