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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
     dumpon [-v] -l

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.

     The default type of kernel	crash dump is the mini crash dump.  Mini crash
     dumps hold	only memory pages in use by the	kernel.	 Alternatively,	full
     memory dumps can be enabled by setting the	debug.minidump sysctl(8) vari-
     able to 0.

     For systems using full memory dumps, 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 memory, so it is	not usually necessary to size
     the dump device larger than the actual amount of RAM available in the
     machine.  Also, when using	full memory dumps, 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 -l flag causes	dumpon to print	the current dump device	or
     _PATH_DEVNULL ("/dev/null") if no device is configured.

     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			April 29, 2013			  FreeBSD 10.1

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

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