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

     dumpon -- specify a device	for crash dumps

     dumpon [-v] special_file
     dumpon [-v] off
     dumpon [-v] -l

     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 con-
     figuration	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 de-
     vice must be at least the size of physical	memory.	 Even though an	addi-
     tional 64 kB header is added to the dump, the BIOS	for a platform typi-
     cally 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 ma-
     chine.  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_DE-
     VNULL ("/dev/null") if no device is configured.

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

     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

     Since dumpon cannot be used during	kernel initialization, the dumpdev
     variable of loader(8) must	be used	to enable dumps	for system panics
     which occur during	kernel initialization.

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

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

     The dumpon	utility	appeared in FreeBSD 2.0.5.

     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.

BSD				October	3, 2016				   BSD


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