NAME¶
dumpon —
specify a device for crash
dumps
SYNOPSIS¶
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 configuration 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 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.
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 sysctl(8) variable.
The
-v flag causes
dumpon to be verbose
about its activity.
IMPLEMENTATION 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 opening
special_file and making a
DIOCSKERNELDUMP ioctl(2) request on
it to save kernel crash dumps. If
special_file is the
text string: “
off”,
dumpon performs a
DIOCSKERNELDUMP
ioctl(2) on
/dev/null and thus instructs
the kernel not to save crash dumps.
FILES¶
- /dev/{ad,da}?s?b
- standard swap areas
- /etc/rc.conf
- boot-time system configuration
SEE ALSO¶
fstab(5),
rc.conf(5),
config(8),
init(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.
