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

NAME
     dumpon - specify a device for crash dumps

SYNOPSIS
     dumpon [-v] special_file
     dumpon [-v] off

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 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 -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.

     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.

SEE ALSO
     fstab(5), rc.conf(5), config(8), init(8), loader(8), rc(8), savecore(8),
     swapon(8), panic(9)

FILES
     /dev/{ad,da}?s?b  standard swap areas
     /etc/rc.conf      boot-time system configuration

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.

HISTORY
     The dumpon utility appeared in FreeBSD 2.1.

FreeBSD 11.0-PRERELEASE          May 12, 1995          FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | IMPLEMENTATION NOTES | SEE ALSO | FILES | BUGS | HISTORY

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