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CRASH(8)                FreeBSD 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
     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 sys-
     tem 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''

     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
     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

     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.

FreeBSD 6.2                    February 2, 1996                    FreeBSD 6.2


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