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 49The 50.Nm 51utility is used to specify a device where the kernel can save a crash dump in 52the case of a panic. 53.Pp 54Calls to 55.Nm 56normally occur from the system multi-user initialization file 57.Pa /etc/rc , 58controlled by the 59.Dq dumpdev 60variable in the boot time configuration file 61.Pa /etc/rc.conf . 62.Pp 63For most systems the size of the specified dump device must be at least 64the size of physical memory. Even though a header is added to the dump 65the BIOS for a platform typically holds back some memory, so you usually 66do not have to size the dump device larger then the actual amount of ram 67you stuffed into the machine. 68.Pp 69The 70.Fl v 71flag causes 72.Nm 73to be verbose about its activity. 74.Sh NOTES 75Since a 76.Xr panic 9 77condition may occur in a situation 78where the kernel cannot trust its internal representation 79of the state of any given filesystem, 80one of the system swap devices, 81and 82.Em not 83a device containing a filesystem, 84should be used as the dump device. 85.Pp 86The 87.Nm 88utility operates by setting the 89.Xr sysctl 3 90MIB variable 91.Dq kern.dumpdev 92to the device number of the designated 93.Ar special_file 94or to 95.Dv NODEV 96(meaning that no dumps are to be taken) if 97.Ar special_file 98is the text string: 99.Dq Li off . 100.Pp 101Since 102.Nm 103cannot be used during kernel initialization, the 104.Va dumpdev 105variable of 106.Xr loader 8 107must be used to enable dumps for system panics which occur 108during kernel initialization. 109.Sh SEE ALSO 110.Xr sysctl 3 , 111.Xr fstab 5 , 112.Xr rc.conf 5 , 113.Xr config 8 , 114.Xr init 8 , 115.Xr loader 8 , 116.Xr rc 8 , 117.Xr savecore 8 , 118.Xr swapon 8 , 119.Xr panic 9 120.Sh FILES 121.Bl -tag -width "/dev/{ad,da}?s?b" -compact 122.It Pa /dev/{ad,da}?s?b 123standard swap areas 124.It Pa /etc/rc.conf 125boot-time system configuration 126.El 127.Sh BUGS 128Because the filesystem layer is already dead by the time a crash dump 129is taken, it is not possible to send crash dumps directly to a file. 130.Sh HISTORY 131The 132.Nm 133utility appeared in 134.Fx 2.1 . 135