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.\" 4. 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.\" $FreeBSD$ 30.\" 31.Dd May 12, 1995 32.Dt DUMPON 8 33.Os 34.Sh NAME 35.Nm dumpon 36.Nd "specify a device for crash dumps" 37.Sh SYNOPSIS 38.Nm 39.Op Fl v 40.Ar special_file 41.Nm 42.Op Fl v 43.Cm off 44.Sh DESCRIPTION 45The 46.Nm 47utility is used to specify a device where the kernel can save a crash dump in 48the case of a panic. 49.Pp 50Calls to 51.Nm 52normally occur from the system multi-user initialization file 53.Pa /etc/rc , 54controlled by the 55.Dq dumpdev 56variable in the boot time configuration file 57.Pa /etc/rc.conf . 58.Pp 59For most systems the size of the specified dump device must be at least 60the size of physical memory. 61Even though an additional header is added to the dump, 62the BIOS for a platform typically holds back some memory, so it is not usually 63necessary to size the dump device larger than the actual amount of RAM 64available in the machine. 65.Pp 66The 67.Fl v 68flag causes 69.Nm 70to be verbose about its activity. 71.Sh IMPLEMENTATION NOTES 72Since a 73.Xr panic 9 74condition may occur in a situation 75where the kernel cannot trust its internal representation 76of the state of any given file system, 77one of the system swap devices, 78and 79.Em not 80a device containing a file system, 81should be used as the dump device. 82.Pp 83The 84.Nm 85utility operates by opening 86.Ar special_file 87and making a 88.Dv DIOCSKERNELDUMP 89.Xr ioctl 2 90request on it to save kernel crash dumps. 91If 92.Ar special_file 93is the text string: 94.Dq Li off , 95.Nm 96performs a 97.Dv DIOCSKERNELDUMP 98.Xr ioctl 2 99on 100.Pa /dev/null 101and thus instructs the kernel not to save crash dumps. 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 SEE ALSO 112.Xr fstab 5 , 113.Xr rc.conf 5 , 114.Xr config 8 , 115.Xr init 8 , 116.Xr loader 8 , 117.Xr rc 8 , 118.Xr savecore 8 , 119.Xr swapon 8 , 120.Xr panic 9 121.Sh FILES 122.Bl -tag -width "/dev/{ad,da}?s?b" -compact 123.It Pa /dev/{ad,da}?s?b 124standard swap areas 125.It Pa /etc/rc.conf 126boot-time system configuration 127.El 128.Sh BUGS 129Because the file system layer is already dead by the time a crash dump 130is taken, it is not possible to send crash dumps directly to a file. 131.Sh HISTORY 132The 133.Nm 134utility appeared in 135.Fx 2.1 . 136