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

     crash -- FreeBSD system failures

     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 inconsis-
     tency 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	rou-
     tine which	detected the error, or a two-word description of the inconsis-
     tency.  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 message 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 sys-
     tem has been corrupted, or	the system is attempting to use	the wrong de-
     vice as root file system.	Usually, an alternate copy of the system bi-
     nary 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	for-
     bids 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 oc-
     cur.  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 ex-
     ited 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 im-
     age 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

     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 (

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

     The crash manual page first appeared in FreeBSD 2.2.

BSD			       February	2, 1996				   BSD


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