a device for crash dumps
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
variable to 0.
For systems using full memory dumps, 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. 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
to print the current dump device or
_PATH_DEVNULL ("/dev/null") if no device is configured.
to be verbose about its activity.
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
a device containing a file system, should be
used as the dump device.
utility operates by opening
and making a
request on it to save kernel crash
dumps. If special_file
is the text string:
and thus instructs the kernel not to
save crash dumps.
cannot be used during kernel
initialization, the dumpdev
must be used to enable dumps for system
panics which occur during kernel initialization.
- standard swap areas
- boot-time system configuration
utility appeared in
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.