Mike Pritchard <mpp@FreeBSD.org>. All rights reserved.
Adapted from share/man/man8/man8.hp300/crash.8
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$FreeBSD: head/share/man/man8/crash.8 79727 2001-07-14 19:41:16Z schweikh $
.Dd February 2, 1996 .Dt CRASH 8 .Os .Sh NAME .Nm crash .Nd FreeBSD system failures .Sh DESCRIPTION This section explains a bit about system crashes and (very briefly) how to analyze crash dumps.
p When the system crashes voluntarily it prints a message of the form d -ragged -offset indent panic: why i gave up the ghost .Ed
p on the console, and if dumps have been enabled (see .Xr dumpon 8 ) , takes a dump on a mass storage peripheral, and then invokes an automatic reboot procedure as described in .Xr 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.
p 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.
p 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.
p l -tag -width Ds -compact t Sy "cannot mount root" This panic message results from a failure to mount the root filesystem during the bootstrap process. Either the root filesystem has been corrupted, or the system is attempting to use the wrong device as root filesystem. Usually, an alternate copy of the system binary or an alternate root filesystem 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.
p t Sy "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, .Xr init 8 . The root filesystem is incorrect or has been corrupted, or the mode or type of
a /sbin/init forbids execution or is totally missing.
p
p t Sy "ffs_realloccg: bad optim" t Sy "ffs_valloc: dup alloc" t Sy "ffs_alloccgblk: cyl groups corrupted" t Sy "ffs_alloccg: map corrupted" t Sy "blkfree: freeing free block" t Sy "blkfree: freeing free frag" t Sy "ifree: freeing free inode" These panic messages are among those that may be produced when filesystem inconsistencies are detected. The problem generally results from a failure to repair damaged filesystems after a crash, hardware failures, or other condition that should not normally occur. A filesystem check will normally correct the problem.
p t Sy "timeout table full" This really shouldn't 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.
p
.It Sy "trap type %d, code = %x, v = %x"
An unexpected trap has occurred within the system; the trap types are:
.Bl -column xxxx -offset indent
0 bus error
1 address error
2 illegal instruction
3 divide by zero
.No 4\t Em chk No instruction
.No 5\t Em trapv No instruction
6 privileged instruction
7 trace trap
8 MMU fault
9 simulated software interrupt
10 format error
11 FP coprocessor fault
12 coprocessor fault
13 simulated AST
.El
.Pp
The favorite trap type in system crashes is trap type 8,
indicating a wild reference.
``code'' (hex) is the concatenation of the
MMU
status register
(see <hp300/cpu.h>)
in the high 16 bits and the 68020 special status word
(see the 68020 manual, page 6-17)
in the low 16.
``v'' (hex) is the virtual address which caused the fault.
Additionally, the kernel will dump about a screenful of semi-useful
information.
``pid'' (decimal) is the process id of the process running at the
time of the exception.
Note that if we panic in an interrupt routine,
this process may not be related to the panic.
``ps'' (hex) is the 68020 processor status register ``ps''.
``pc'' (hex) is the value of the program counter saved
on the hardware exception frame.
It may
.Em not
be the PC of the instruction causing the fault.
``sfc'' and ``dfc'' (hex) are the 68020 source/destination function codes.
They should always be one.
``p0'' and ``p1'' are the
VAX-like
region registers.
They are of the form:
.Pp
.Bd -ragged -offset indent
<length> '@' <kernel VA>
.Ed
.Pp
where both are in hex.
Following these values are a dump of the processor registers (hex).
Finally, is a dump of the stack (user/kernel) at the time of the offense.
.Pp
t Sy "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.
.El
p That completes the list of panic types you are likely to see.
p If the system has been configured to take crash dumps (see .Xr 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 .Xr savecore 8 runs and preserves a copy of this core image and the current system in a specified directory for later perusal. See .Xr savecore 8 for details.
p To analyze a dump you should begin by running .Xr gdb 1 with the .Fl 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 .Fx handbook
q Pa http://www.FreeBSD.org . .Sh SEE ALSO .Xr gdb 1 , .Xr dumpon 8 , .Xr reboot 8 , .Xr savecore 8 .Sh HISTORY A .Nm man page first appeared in .Fx 2.2 .