217 lines
7.8 KiB
Groff
217 lines
7.8 KiB
Groff
.\" FreeBSD version Copyright (c) 1996
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.\" Mike Pritchard <mpp@FreeBSD.org>. All rights reserved.
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.\"
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.\" Adapted from share/man/man8/man8.hp300/crash.8
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.\"
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.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 23, 2011
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.Dt CRASH 8
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.Os
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.Sh NAME
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.Nm crash
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.Nd FreeBSD system failures
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.Sh DESCRIPTION
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This section explains a bit about system crashes
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and (very briefly) how to analyze crash dumps.
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.Pp
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When the system crashes voluntarily it prints a message of the form
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.Bl -diag -offset indent
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.It "panic: why i gave up the ghost"
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.El
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.Pp
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on the console, and if dumps have been enabled (see
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.Xr dumpon 8 ) ,
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takes a dump on a mass storage peripheral,
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and then invokes an automatic reboot procedure as
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described in
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.Xr reboot 8 .
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Unless some unexpected inconsistency is encountered in the state
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of the file systems due to hardware or software failure, the system
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will then resume multi-user operations.
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.Pp
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The system has a large number of internal consistency checks; if one
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of these fails, then it will panic with a very short message indicating
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which one failed.
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In many instances, this will be the name of the routine which detected
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the error, or a two-word description of the inconsistency.
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A full understanding of most panic messages requires perusal of the
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source code for the system.
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.Pp
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The most common cause of system failures is hardware failure, which
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can reflect itself in different ways.
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Here are the messages which
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are most likely, with some hints as to causes.
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Left unstated in all cases is the possibility that hardware or software
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error produced the message in some unexpected way.
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.Pp
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.Bl -diag -compact
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.It "cannot mount root"
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This panic message results from a failure to mount the root file system
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during the bootstrap process.
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Either the root file system has been corrupted,
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or the system is attempting to use the wrong device as root file system.
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Usually, an alternate copy of the system binary or an alternate root
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file system can be used to bring up the system to investigate.
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Most often
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this is done by the use of the boot floppy you used to install the system,
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and then using the
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.Dq fixit
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floppy.
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.Pp
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.It "init: not found"
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This is not a panic message, as reboots are likely to be futile.
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Late in the bootstrap procedure, the system was unable to locate
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and execute the initialization process,
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.Xr init 8 .
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The root file system is incorrect or has been corrupted, or the mode
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or type of
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.Pa /sbin/init
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forbids execution or is totally missing.
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.Pp
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.It "ffs_realloccg: bad optim"
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.It "ffs_valloc: dup alloc"
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.It "ffs_alloccgblk: cyl groups corrupted"
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.It "ffs_alloccg: map corrupted"
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.It "blkfree: freeing free block"
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.It "blkfree: freeing free frag"
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.It "ifree: freeing free inode"
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These panic messages are among those that may be produced
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when file system inconsistencies are detected.
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The problem generally results from a failure to repair damaged file systems
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after a crash, hardware failures, or other condition that should not
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normally occur.
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A file system check will normally correct the problem.
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.Pp
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.It "timeout table full"
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This really should not be a panic, but until the data structure
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involved is made to be extensible, running out of entries causes a crash.
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If this happens, make the timeout table bigger.
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.Pp
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.\" .It "trap type %d, code = %x, v = %x"
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.\" An unexpected trap has occurred within the system; the trap types are:
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.\" .Bl -column xxxx -offset indent
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.\" 0 bus error
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.\" 1 address error
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.\" 2 illegal instruction
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.\" 3 divide by zero
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.\" .No 4\t Em chk No instruction
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.\" .No 5\t Em trapv No instruction
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.\" 6 privileged instruction
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.\" 7 trace trap
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.\" 8 MMU fault
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.\" 9 simulated software interrupt
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.\" 10 format error
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.\" 11 FP coprocessor fault
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.\" 12 coprocessor fault
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.\" 13 simulated AST
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.\" .El
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.\" .Pp
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.\" The favorite trap type in system crashes is trap type 8,
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.\" indicating a wild reference.
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.\" ``code'' (hex) is the concatenation of the
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.\" MMU
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.\" status register
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.\" (see <hp300/cpu.h>)
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.\" in the high 16 bits and the 68020 special status word
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.\" (see the 68020 manual, page 6-17)
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.\" in the low 16.
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.\" ``v'' (hex) is the virtual address which caused the fault.
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.\" Additionally, the kernel will dump about a screenful of semi-useful
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.\" information.
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.\" ``pid'' (decimal) is the process id of the process running at the
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.\" time of the exception.
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.\" Note that if we panic in an interrupt routine,
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.\" this process may not be related to the panic.
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.\" ``ps'' (hex) is the 68020 processor status register ``ps''.
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.\" ``pc'' (hex) is the value of the program counter saved
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.\" on the hardware exception frame.
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.\" It may
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.\" .Em not
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.\" be the PC of the instruction causing the fault.
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.\" ``sfc'' and ``dfc'' (hex) are the 68020 source/destination function codes.
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.\" They should always be one.
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.\" ``p0'' and ``p1'' are the
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.\" VAX-like
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.\" region registers.
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.\" They are of the form:
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.\" .Pp
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.\" .Bd -ragged -offset indent
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.\" <length> '@' <kernel VA>
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.\" .Ed
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.\" .Pp
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.\" where both are in hex.
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.\" Following these values are a dump of the processor registers (hex).
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.\" Finally, is a dump of the stack (user/kernel) at the time of the offense.
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.\" .Pp
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.It "init died (signal #, exit #)"
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The system initialization process has exited with the specified
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signal number and exit code.
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This is bad news, as no new users will then be able to log in.
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Rebooting is the only fix, so the
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system just does it right away.
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.El
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.Pp
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That completes the list of panic types you are likely to see.
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.Pp
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If the system has been configured to take crash dumps (see
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.Xr dumpon 8 ) ,
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then when it crashes it will write (or at least attempt to write)
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an image of memory into the back end of the dump device,
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usually the same as the primary swap
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area.
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After the system is rebooted, the program
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.Xr savecore 8
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runs and preserves a copy of this core image and the current
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system in a specified directory for later perusal.
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See
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.Xr savecore 8
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for details.
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.Pp
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To analyze a dump you should begin by running
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.Xr kgdb 1
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on the system load image and core dump.
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If the core image is the result of a panic,
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the panic message is printed.
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For more details consult the chapter on kernel debugging in
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the
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.%B "FreeBSD Developers' Handbook"
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.Pq Pa https://www.freebsd.org/doc/en/books/developers-handbook/ .
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.Sh SEE ALSO
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.Xr kgdb 1 ,
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.Xr dumpon 8 ,
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.Xr reboot 8 ,
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.Xr savecore 8
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.Sh HISTORY
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The
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.Nm
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manual page first appeared in
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.Fx 2.2 .
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