240 lines
8.4 KiB
Groff
240 lines
8.4 KiB
Groff
.\" Copyright (c) 1980, 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. 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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.\" @(#)crash.8 8.1 (Berkeley) 6/5/93
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.\"
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.TH CRASH 8 "June 5, 1993"
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.UC 4
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.SH NAME
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crash \- UNIX system failures
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.SH DESCRIPTION
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This section explains what happens when the 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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.IP
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panic: why i gave up the ghost
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.LP
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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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.IR reboot (8).
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(If auto-reboot is disabled on the front panel of the machine the system
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will simply halt at this point.)
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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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.TP
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.B 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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.TP
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.B Can't exec /sbin/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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.IR 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 /sbin/init forbids execution.
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.TP
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.B IO err in push
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.ns
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.TP
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.B 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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.TP
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.B realloccg: bad optim
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.ns
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.TP
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.B ialloc: dup alloc
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.ns
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.TP
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.B alloccgblk: cyl groups corrupted
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.ns
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.TP
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.B ialloccg: map corrupted
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.ns
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.TP
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.B free: freeing free block
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.ns
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.TP
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.B free: freeing free frag
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.ns
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.TP
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.B ifree: freeing free inode
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.ns
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.TP
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.B 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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.TP
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.B timeout table overflow
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.ns
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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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.TP
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.B KSP not valid
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.ns
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.TP
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.B SBI fault
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.ns
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.TP
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.B CHM? in kernel
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These indicate either a serious bug in the system or, more often,
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a glitch or failing hardware.
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If SBI faults recur, check out the hardware or call
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field service. If the other faults recur, there is likely a bug somewhere
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in the system, although these can be caused by a flakey processor.
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Run processor microdiagnostics.
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.TP
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.B machine check %x:
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.I description
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.ns
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.TP
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.I \0\0\0machine dependent machine-check information
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.ns
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Machine checks are different on each type of CPU.
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Most of the internal processor registers are saved at the time of the fault
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and are printed on the console.
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For most processors, there is one line that summarizes the type of machine
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check.
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Often, the nature of the problem is apparent from this messaage
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and/or the contents of key registers.
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The VAX Hardware Handbook should be consulted,
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and, if necessary, your friendly field service people should be informed
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of the problem.
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.TP
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.B trap type %d, code=%x, pc=%x
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A unexpected trap has occurred within the system; the trap types are:
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.sp
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.nf
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0 reserved addressing fault
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1 privileged instruction fault
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2 reserved operand fault
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3 bpt instruction fault
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4 xfc instruction fault
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5 system call trap
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6 arithmetic trap
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7 ast delivery trap
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8 segmentation fault
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9 protection fault
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10 trace trap
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11 compatibility mode fault
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12 page fault
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13 page table fault
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.fi
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.sp
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The favorite trap types in system crashes are trap types 8 and 9,
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indicating
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a wild reference. The code is the referenced address, and the pc at the
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time of the fault is printed. These problems tend to be easy to track
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down if they are kernel bugs since the processor stops cold, but random
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flakiness seems to cause this sometimes.
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The debugger can be used to locate the instruction and subroutine
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corresponding to the PC value.
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If that is insufficient to suggest the nature of the problem,
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more detailed examination of the system status at the time of the trap
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usually can produce an explanation.
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.TP
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.B 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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.TP
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.B 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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.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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.IR 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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.IR 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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.IR adb (1)
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with the
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.B \-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 detail
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see
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``Using ADB to Debug the UNIX Kernel''.
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.SH "SEE ALSO"
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adb(1),
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reboot(8)
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.br
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.I "VAX 11/780 System Maintenance Guide"
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and
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.I "VAX Hardware Handbook"
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for more information about machine checks.
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.br
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.I "Using ADB to Debug the UNIX Kernel"
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