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DUMPON(8)              DragonFly System Manager's Manual             DUMPON(8)


NAME

     dumpon, dumpoff - specify a device for crash dumps


SYNOPSIS

     dumpon special_file
     dumpon off
     dumpoff


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.

     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), 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.

DragonFly 5.7-DEVELOPMENT     September 23, 2018     DragonFly 5.7-DEVELOPMENT

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