227 lines
8.1 KiB
Groff
227 lines
8.1 KiB
Groff
.\" Copyright (c) 1990, 1991 Regents of the University of California.
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.\" 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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. 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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.\" from: @(#)crash.8 5.2 (Berkeley) 3/16/91
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.\" $Id: crash.8,v 1.2 1993/08/01 07:55:13 mycroft Exp $
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.\"
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.Dd March 16, 1991
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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 UNIX 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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.Bd -ragged -offset indent
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panic: why i gave up the ghost
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.Ed
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.Pp
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on the console, 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. 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 -tag -width Ds -compact
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.It Sy iinit
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This cryptic panic message results from a failure to mount the root filesystem
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during the bootstrap process.
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Either the root filesystem has been corrupted,
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or the system is attempting to use the wrong device as root filesystem.
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Usually, an alternate copy of the system binary or an alternate root
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filesystem can be used to bring up the system to investigate.
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.Pp
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.It Sy "Can't exec /etc/init"
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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 filesystem is incorrect or has been corrupted, or the mode
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or type of
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.Pa /etc/init
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forbids execution.
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.Pp
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.It Sy "IO err in push"
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.It Sy "hard IO err in swap"
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The system encountered an error trying to write to the paging device
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or an error in reading critical information from a disk drive.
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The offending disk should be fixed if it is broken or unreliable.
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.Pp
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.It Sy "realloccg: bad optim"
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.It Sy "ialloc: dup alloc"
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.It Sy "alloccgblk:cyl groups corrupted"
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.It Sy "ialloccg: map corrupted"
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.It Sy "free: freeing free block"
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.It Sy "free: freeing free frag"
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.It Sy "ifree: freeing free inode"
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.It Sy "alloccg: map corrupted"
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These panic messages are among those that may be produced
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when filesystem inconsistencies are detected.
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The problem generally results from a failure to repair damaged filesystems
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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 filesystem check will normally correct the problem.
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.Pp
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.It Sy "timeout table overflow"
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This really shouldn't 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 Sy "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 Sy "init died"
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The system initialization process has exited. This is bad news, as no new
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users will then be able to log in. Rebooting is the only fix, so the
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system just does it right away.
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.Pp
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.It Sy "out of mbufs: map full"
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The network has exhausted its private page map for network buffers.
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This usually indicates that buffers are being lost, and rather than
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allow the system to slowly degrade, it reboots immediately.
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The map may be made larger if necessary.
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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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When the system crashes it writes (or at least attempts 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. 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. 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 adb 1
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with the
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.Fl k
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flag 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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Normally the command
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``$c''
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will provide a stack trace from the point of
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the crash and this will provide a clue as to
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what went wrong.
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For more details consult
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.%T "Using ADB to Debug the UNIX Kernel" .
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.Sh SEE ALSO
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.Xr adb 1 ,
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.Xr reboot 8
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.Rs
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.%T "MC68020 32-bit Microprocessor User's Manual"
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.Re
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.Rs
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.%T "Using ADB to Debug the UNIX Kernel
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.Re
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.Rs
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.%T "4.3BSD for the HP300"
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.Re
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.Sh HISTORY
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A
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.Nm
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man page appeared in Version 6 AT&T UNIX.
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