|DUMPON(8)||System Manager's Manual||DUMPON(8)|
dumpon — specify a
device for crash dumps
dumpon utility is used to specify a
device where the kernel can save a crash dump in the case of a panic.
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 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
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.
-l flag causes
dumpon to print the current dump device or
_PATH_DEVNULL ("/dev/null") if no device is configured.
-v flag causes
dumpon 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 not a device containing a file system, should be used as the dump device.
dumpon utility operates by opening
special_file and making a
DIOCSKERNELDUMP ioctl(2) request
on it to save kernel crash dumps. If special_file is
the text string: “
dumpon performs a
DIOCSKERNELDUMP ioctl(2) on
/dev/null and thus instructs the kernel not to save
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.
- standard swap areas
- boot-time system configuration
dumpon 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.
|October 8, 2014||Debian|