dumpon(8)

NAME

dumpon - specify a device for crash dumps

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

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 memory, 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 cannot trust its internal representation of the state of any
given file system, one of the system swap devices, and not a device con
taining a file system, should be used as the dump device.
The dumpon utility operates by opening special_file and mak
ing 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.

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

The dumpon utility appeared in FreeBSD 2.1.