DUMPON(8)

NAME
dumpon - specify a device for crash dumps

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

DESCRIPTION
Dumpon 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 size of the specified dump device must be at least 64 KB greater the size of physical memory.

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

NOTES
One of the system swap devices is usually chosen as the dump device, as swap devices are the most likely to have the required space at dump time.

The dump device can also be specified at kernel compile time using the “dumps on” clause in the kernel configuration file (see config(8) ). This is useful when the kernel panics before multi-user mode is reached. Subsequent successful invocations of dumpon will override the compiled in value.

The dumpon program 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”.

SEE ALSO
sysctl(3), fstab(5), rc.conf(5), init(8), config(8), rc(8), savecore(8), swapon(8), panic(9)

FILES
/dev/[ws]d?b
    standard swap areas
/etc/rc.conf
    boot-time system configuration

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

Dumpon currently allows only devices with minor number 1 to be used as dump devices.

HISTORY
The dumpon command appeared in FreeBSD 2.1.