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.\" 31.Dd September 23, 2018 32.Dt DUMPON 8 33.Os 34.Sh NAME 35.Nm dumpon , dumpoff 36.Nd "specify a device for crash dumps" 37.Sh SYNOPSIS 38.Nm 39.Ar special_file 40.Nm 41.Cm off 42.Nm dumpoff 43.Sh DESCRIPTION 44The 45.Nm 46utility is used to specify a device where the kernel can save a crash dump in 47the case of a panic. 48.Pp 49Calls to 50.Nm 51normally occur from the system multi-user initialization file 52.Pa /etc/rc , 53controlled by the 54.Dq dumpdev 55variable in the boot time configuration file 56.Pa /etc/rc.conf . 57.Pp 58The default type of kernel crash dump is the mini crash dump. 59Mini crash dumps hold only memory pages in use by the kernel. 60Alternatively, full memory dumps can be enabled by setting the 61.Va debug.minidump 62.Xr sysctl 8 63variable to 0. 64.Pp 65For most systems the size of the specified dump device must be at least 66the size of physical memory. 67Even though an additional header is added to the dump, 68the BIOS for a platform typically holds back some memory, so it is not usually 69necessary to size the dump device larger than the actual amount of RAM 70available in the machine. 71.Sh 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 setting the 86.Xr sysctl 3 87MIB variable 88.Va kern.dumpdev 89to the device number of the designated 90.Ar special_file 91or to 92.Dv NODEV 93(meaning that no dumps are to be taken) if the utility is invoked as 94.Nm dumpoff 95or if 96.Ar special_file 97is the text string: 98.Dq Li off . 99.Pp 100In order to change the device for crash dumps, one needs to run the 101.Nm dumpoff 102utility to disable the current dump device before configuring the new one. 103.Pp 104Since 105.Nm 106cannot be used during kernel initialization, the 107.Va dumpdev 108variable of 109.Xr loader 8 110must be used to enable dumps for system panics which occur 111during kernel initialization. 112.Sh FILES 113.Bl -tag -width "/dev/{ad,da}?s?b" -compact 114.It Pa /dev/{ad,da}?s?b 115standard swap areas 116.It Pa /etc/rc.conf 117boot-time system configuration 118.El 119.Sh SEE ALSO 120.Xr sysctl 3 , 121.Xr fstab 5 , 122.Xr rc.conf 5 , 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 2.0.5 . 134The 135.Nm dumpoff 136utility first appeared in 137.Dx 5.3 . 138.Sh BUGS 139Because the file system layer is already dead by the time a crash dump 140is taken, it is not possible to send crash dumps directly to a file. 141