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.Nm 45.Op Fl v 46.Fl l 47.Sh DESCRIPTION 48The 49.Nm 50utility is used to specify a device where the kernel can save a crash 51dump in the 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 62For most systems the size of the specified dump device must be at 63least the size of physical memory. 64Even though an additional 64 kB header is added to the dump, the BIOS for a 65platform typically holds back some memory, so it is not usually 66necessary to size the dump device larger than the actual amount of RAM 67available in the machine. 68.Pp 69The 70.Nm 71utility will refuse to enable a dump device which is smaller than the 72total amount of physical memory as reported by the 73.Va hw.physmem 74.Xr sysctl 8 75variable. 76.Pp 77The 78.Fl l 79flag causes 80.Nm 81to print the current dump device or _PATH_DEVNULL ("/dev/null") if no device is 82configured. 83.Pp 84The 85.Fl v 86flag causes 87.Nm 88to be verbose about its activity. 89.Sh IMPLEMENTATION NOTES 90Since a 91.Xr panic 9 92condition may occur in a situation 93where the kernel cannot trust its internal representation 94of the state of any given file system, 95one of the system swap devices, 96and 97.Em not 98a device containing a file system, 99should be used as the dump device. 100.Pp 101The 102.Nm 103utility operates by opening 104.Ar special_file 105and making a 106.Dv DIOCSKERNELDUMP 107.Xr ioctl 2 108request on it to save kernel crash dumps. 109If 110.Ar special_file 111is the text string: 112.Dq Li off , 113.Nm 114performs a 115.Dv DIOCSKERNELDUMP 116.Xr ioctl 2 117on 118.Pa /dev/null 119and thus instructs the kernel not to save crash dumps. 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 SEE ALSO 128.Xr fstab 5 , 129.Xr rc.conf 5 , 130.Xr config 8 , 131.Xr init 8 , 132.Xr rc 8 , 133.Xr savecore 8 , 134.Xr swapon 8 , 135.Xr panic 9 136.Sh HISTORY 137The 138.Nm 139utility appeared in 140.Fx 2.1 . 141.Sh BUGS 142Because the file system layer is already dead by the time a crash dump 143is taken, it is not possible to send crash dumps directly to a file. 144