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 October 8, 2014 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 62The default type of kernel crash dump is the mini crash dump. 63Mini crash dumps hold only memory pages in use by the kernel. 64Alternatively, full memory dumps can be enabled by setting the 65.Va debug.minidump 66.Xr sysctl 8 67variable to 0. 68.Pp 69For systems using full memory dumps, the size of the specified dump 70device must be at 71least the size of physical memory. 72Even though an additional 64 kB header is added to the dump, the BIOS for a 73platform typically holds back some memory, so it is not usually 74necessary to size the dump device larger than the actual amount of RAM 75available in the machine. 76Also, when using full memory dumps, the 77.Nm 78utility will refuse to enable a dump device which is smaller than the 79total amount of physical memory as reported by the 80.Va hw.physmem 81.Xr sysctl 8 82variable. 83.Pp 84The 85.Fl l 86flag causes 87.Nm 88to print the current dump device or _PATH_DEVNULL ("/dev/null") if no device is 89configured. 90.Pp 91The 92.Fl v 93flag causes 94.Nm 95to be verbose about its activity. 96.Sh IMPLEMENTATION NOTES 97Since a 98.Xr panic 9 99condition may occur in a situation 100where the kernel cannot trust its internal representation 101of the state of any given file system, 102one of the system swap devices, 103and 104.Em not 105a device containing a file system, 106should be used as the dump device. 107.Pp 108The 109.Nm 110utility operates by opening 111.Ar special_file 112and making a 113.Dv DIOCSKERNELDUMP 114.Xr ioctl 2 115request on it to save kernel crash dumps. 116If 117.Ar special_file 118is the text string: 119.Dq Li off , 120.Nm 121performs a 122.Dv DIOCSKERNELDUMP 123.Xr ioctl 2 124on 125.Pa /dev/null 126and thus instructs the kernel not to save crash dumps. 127.Pp 128Since 129.Nm 130cannot be used during kernel initialization, the 131.Va dumpdev 132variable of 133.Xr loader 8 134must be used to enable dumps for system panics which occur 135during kernel initialization. 136.Sh FILES 137.Bl -tag -width "/dev/{ada,da}?s?b" -compact 138.It Pa /dev/{ada,da}?s?b 139standard swap areas 140.It Pa /etc/rc.conf 141boot-time system configuration 142.El 143.Sh SEE ALSO 144.Xr fstab 5 , 145.Xr rc.conf 5 , 146.Xr config 8 , 147.Xr init 8 , 148.Xr loader 8 , 149.Xr rc 8 , 150.Xr savecore 8 , 151.Xr swapon 8 , 152.Xr panic 9 153.Sh HISTORY 154The 155.Nm 156utility appeared in 157.Fx 2.1 . 158.Sh BUGS 159Because the file system layer is already dead by the time a crash dump 160is taken, it is not possible to send crash dumps directly to a file. 161