NAME
dumpon, dumpoff
— specify a device for crash
dumps
SYNOPSIS
dumpon |
special_file |
dumpon |
off |
dumpoff |
DESCRIPTION
Thedumpon 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) variable to 0.
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.
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 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 the
utility is invoked as dumpoff or if
special_file is the text string:
“off”.
In order to change the device for crash dumps, one needs to run
the dumpoff utility to disable the current dump
device before configuring the new one.
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 ALSO
sysctl(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 2.0.5. The dumpoff
utility first appeared in DragonFly 5.3.
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.