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DUMPON(8)		FreeBSD	System Manager's Manual		     DUMPON(8)

NAME
     dumpon -- specify a device	for crash dumps

SYNOPSIS
     dumpon [-v] special_file
     dumpon [-v] off

DESCRIPTION
     The dumpon	utility	is used	to specify a device where the kernel can save
     a crash dump in the case of a panic.

     Calls to dumpon normally occur from the system multi-user initialization
     file /etc/rc, controlled by the ``dumpdev'' variable in the boot time
     configuration file	/etc/rc.conf.

     For most systems the size of the specified	dump device must be at least
     the size of physical memory.  Even	though an additional 64	kB header is
     added to the dump,	the BIOS for a platform	typically holds	back some mem-
     ory, so it	is not usually necessary to size the dump device larger	than
     the actual	amount of RAM available	in the machine.

     The dumpon	utility	will refuse to enable a	dump device which is smaller
     than the total amount of physical memory as reported by the hw.physmem
     sysctl(8) variable.

     The -v flag causes	dumpon to be verbose about its activity.

IMPLEMENTATION NOTES
     Since a panic(9) condition	may occur in a situation where the kernel can-
     not trust its internal representation of the state	of any given file sys-
     tem, one of the system swap devices, and not a device containing a	file
     system, should be used as the dump	device.

     The dumpon	utility	operates by opening special_file and making a
     DIOCSKERNELDUMP ioctl(2) request on it to save kernel crash dumps.	 If
     special_file is the text string: ``off'', dumpon performs a
     DIOCSKERNELDUMP ioctl(2) on /dev/null and thus instructs the kernel not
     to	save crash dumps.

FILES
     /dev/{ad,da}?s?b  standard	swap areas
     /etc/rc.conf      boot-time system	configuration

SEE ALSO
     fstab(5), rc.conf(5), config(8), init(8), rc(8), savecore(8), swapon(8),
     panic(9)

HISTORY
     The dumpon	utility	appeared in FreeBSD 2.1.

BUGS
     Because the file system layer is already dead by the time a crash dump is
     taken, it is not possible to send crash dumps directly to a file.

FreeBSD	10.1			 May 12, 1995			  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | IMPLEMENTATION NOTES | FILES | SEE ALSO | HISTORY | BUGS

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