DUMPON(8) BSD System Manager's Manual DUMPON(8)NAMEdumpon — specify a device for crash dumps
SYNOPSISdumpon [-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 con‐
figuration 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 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 -v flag causes dumpon to be verbose about its activity.
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 setting the sysctl(3) MIB variable
kern.dumpdev to the device number of the designated special_file or to
NODEV (meaning that no dumps are to be taken) if special_file is the text
string: “off”.
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.
FILES
/dev/{ad,da}?s?b standard swap areas
/etc/rc.conf boot-time system configuration
SEE ALSOsysctl(3), fstab(5), rc.conf(5), config(8), init(8), loader(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.
BSD May 12, 1995 BSD