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 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 inconsistency.
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
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''
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
To analyze a dump you should begin by running gdb(1) with the -k flag 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
gdb(1), dumpon(8), reboot(8), savecore(8)
A crash man page first appeared in FreeBSD 2.2.
FreeBSD 5.2.1 February 2, 1996 FreeBSD 5.2.1 [ Back ]