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.\" $FreeBSD$ 34.\" 35.Dd May 12, 1995 36.Dt DUMPON 8 37.Os 38.Sh NAME 39.Nm dumpon 40.Nd "specify a device for crash dumps" 41.Sh SYNOPSIS 42.Nm 43.Op Fl v 44.Ar special_file 45.Nm 46.Op Fl v 47.Ar off 48.Sh DESCRIPTION 49.Nm Dumpon 50is used to specify a device where the kernel can save a crash dump in 51the case of a panic. 52.Pp 53Calls to 54.Nm 55normally occur from the system multi-user initialization file 56.Pa /etc/rc , 57controlled by the 58.Dq dumpdev 59variable in the boot time configuration file 60.Pa /etc/rc.conf . 61.Pp 62The size of the specified dump device must be at least 64 KB greater 63than the size of physical memory. 64.Pp 65The 66.Fl v 67flag causes 68.Nm 69to be verbose about its activity. 70.Sh NOTES 71Since a 72.Xr panic 9 73condition may occur in a situation 74where the kernel cannot trust its internal representation 75of the state of any given filesystem, 76one of the system swap devices, 77and 78.Em not 79a device containing a filesystem, 80should be used as the dump device. 81.Pp 82The 83.Nm 84program operates by setting the 85.Xr sysctl 3 86MIB variable 87.Dq kern.dumpdev 88to the device number of the designated 89.Ar special_file 90or to 91.Dv NODEV 92(meaning that no dumps are to be taken) if 93.Ar special_file 94is the text string: 95.Dq Li off . 96.Sh SEE ALSO 97.Xr sysctl 3 , 98.Xr fstab 5 , 99.Xr rc.conf 5 , 100.Xr config 8 , 101.Xr init 8 , 102.Xr rc 8 , 103.Xr savecore 8 , 104.Xr swapon 8 , 105.Xr panic 9 106.Sh FILES 107.Bl -tag -width "/dev/{ad,da}?s?b" -compact 108.It Pa /dev/{ad,da}?s?b 109standard swap areas 110.It Pa /etc/rc.conf 111boot-time system configuration 112.El 113.Sh BUGS 114Because the filesystem layer is already dead by the time a crash dump 115is taken, it is not possible to send crash dumps directly to a file. 116.Pp 117Since 118.Nm 119can only be called after the system enters single-user mode, 120it can not be used to create dumps 121for system panics during kernel initialization. 122.Sh HISTORY 123The 124.Nm 125command appeared in 126.Fx 2.1 . 127