dumpon(8) [freebsd man page]

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

NAME

     dumpon -- specify a device for crash dumps

SYNOPSIS

     dumpon [-v] special_file
     dumpon [-v] off
     dumpon [-v] -l

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 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 sysctl(8) vari-
     able.

     The -l flag causes dumpon to print the current dump device or _PATH_DEVNULL ("/dev/null") if no device is configured.

     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.

FILES

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

SEE ALSO

     fstab(5), rc.conf(5), config(8), init(8), loader(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.

BSD
								  October 8, 2014							       BSD

CRASH(8)						    BSD System Manager's Manual 						  CRASH(8)

NAME

     crash -- FreeBSD system failures

DESCRIPTION

     This section explains a bit about system crashes and (very briefly) how to analyze crash dumps.

     When the system crashes voluntarily it prints a message of the form

	   panic: why i gave up the ghost

     on the console, and if dumps have been enabled (see dumpon(8)), takes a dump on a mass storage peripheral, and then invokes an automatic
     reboot procedure as described in reboot(8).  Unless some unexpected inconsistency is encountered in the state of the file systems due to
     hardware or software failure, the system will then resume multi-user operations.

     The system has a large number of internal consistency checks; if one of these fails, then it will panic with a very short message indicating
     which one failed.	In many instances, this will be the name of the routine which detected the error, or a two-word description of the incon-
     sistency.	A full understanding of most panic messages requires perusal of the source code for the system.

     The most common cause of system failures is hardware failure, which can reflect itself in different ways.	Here are the messages which are
     most likely, with some hints as to causes.  Left unstated in all cases is the possibility that hardware or software error produced the mes-
     sage in some unexpected way.

     cannot mount root	This panic message results from a failure to mount the root file system during the bootstrap process.  Either the root
     file system has been corrupted, or the system is attempting to use the wrong device as root file system.  Usually, an alternate copy of the
     system binary or an alternate root file system can be used to bring up the system to investigate.	Most often this is done by the use of the
     boot floppy you used to install the system, and then using the ``fixit'' floppy.

     init: not found  This is not a panic message, as reboots are likely to be futile.	Late in the bootstrap procedure, the system was unable to
     locate and execute the initialization process, init(8).  The root file system is incorrect or has been corrupted, or the mode or type of
     /sbin/init forbids execution or is totally missing.

     ffs_realloccg: bad optim
     ffs_valloc: dup alloc
     ffs_alloccgblk: cyl groups corrupted
     ffs_alloccg: map corrupted
     blkfree: freeing free block
     blkfree: freeing free frag
     ifree: freeing free inode	These panic messages are among those that may be produced when file system inconsistencies are detected.  The
     problem generally results from a failure to repair damaged file systems after a crash, hardware failures, or other condition that should not
     normally occur.  A file system check will normally correct the problem.

     timeout table full  This really should not be a panic, but until the data structure involved is made to be extensible, running out of entries
     causes a crash.  If this happens, make the timeout table bigger.

     init died (signal #, exit #)  The system initialization process has exited with the specified signal number and exit code.  This is bad news,
     as no new users will then be able to log in.  Rebooting is the only fix, so the system just does it right away.

     That completes the list of panic types you are likely to see.

     If the system has been configured to take crash dumps (see dumpon(8)), then when it crashes it will write (or at least attempt to write) an
     image of memory into the back end of the dump device, usually the same as the primary swap area.  After the system is rebooted, the program
     savecore(8) runs and preserves a copy of this core image and the current system in a specified directory for later perusal.  See savecore(8)
     for details.

     To analyze a dump you should begin by running kgdb(1) on the system load image and core dump.  If the core image is the result of a panic,
     the panic message is printed.  For more details consult the chapter on kernel debugging in the FreeBSD Developers' Handbook
     (http://www.freebsd.org/doc/en/books/developers-handbook/).

SEE ALSO

     kgdb(1), dumpon(8), reboot(8), savecore(8)

HISTORY

     The crash manual page first appeared in FreeBSD 2.2.

BSD
								   July 23, 2011							       BSD