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 48dump in the 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 60least the size of physical memory. 61Even though an additional 64 kB header is added to the dump, the BIOS for a 62platform 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.Nm 68utility will refuse to enable a dump device which is smaller than the 69total amount of physical memory as reported by the 70.Va hw.physmem 71.Xr sysctl 8 72variable. 73.Pp 74The 75.Fl v 76flag causes 77.Nm 78to be verbose about its activity. 79.Sh IMPLEMENTATION NOTES 80Since a 81.Xr panic 9 82condition may occur in a situation 83where the kernel cannot trust its internal representation 84of the state of any given file system, 85one of the system swap devices, 86and 87.Em not 88a device containing a file system, 89should be used as the dump device. 90.Pp 91The 92.Nm 93utility operates by opening 94.Ar special_file 95and making a 96.Dv DIOCSKERNELDUMP 97.Xr ioctl 2 98request on it to save kernel crash dumps. 99If 100.Ar special_file 101is the text string: 102.Dq Li off , 103.Nm 104performs a 105.Dv DIOCSKERNELDUMP 106.Xr ioctl 2 107on 108.Pa /dev/null 109and thus instructs the kernel not to save crash dumps. 110.Sh FILES 111.Bl -tag -width "/dev/{ad,da}?s?b" -compact 112.It Pa /dev/{ad,da}?s?b 113standard swap areas 114.It Pa /etc/rc.conf 115boot-time system configuration 116.El 117.Sh SEE ALSO 118.Xr fstab 5 , 119.Xr rc.conf 5 , 120.Xr config 8 , 121.Xr init 8 , 122.Xr rc 8 , 123.Xr savecore 8 , 124.Xr swapon 8 , 125.Xr panic 9 126.Sh HISTORY 127The 128.Nm 129utility appeared in 130.Fx 2.1 . 131.Sh BUGS 132Because the file system layer is already dead by the time a crash dump 133is taken, it is not possible to send crash dumps directly to a file. 134