113 lines
3.5 KiB
Groff
113 lines
3.5 KiB
Groff
.\" $NetBSD: panic.9,v 1.22 2018/07/15 05:16:41 maxv Exp $
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.\"
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.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" Michael Graff.
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd July 14, 2018
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.Dt PANIC 9
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.Os
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.Sh NAME
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.Nm panic
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.Nd bring down system on fatal error
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/systm.h
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.Ft void
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.Fn vpanic "const char *fmt" "va_list ap"
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.Ft void
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.Fn panic "const char *fmt" "..."
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.Sh DESCRIPTION
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The
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.Fn panic
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and
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.Fn vpanic
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functions terminate the
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.Nx
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system.
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The message
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.Fa fmt
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is a
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.Xr printf 3
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style format string which is printed to the console and saved in the
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variable
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.Va panicstr
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for later retrieval via core dump inspection.
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A newline character is added at the end automatically, and is thus
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not needed in the format string.
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.Pp
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If a kernel debugger is installed, control is passed to it after the
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message is printed.
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If the kernel debugger is
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.Xr ddb 4 ,
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control may be passed to it, depending on the value of
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.Em ddb.onpanic .
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See
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.Xr options 4
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for more details on setting
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.Em ddb.onpanic .
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If control is not passed through to
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.Xr ddb 4 ,
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a
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.Xr ddb 4 Ns -specific
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function is used to print the kernel stack trace, and then control returns
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to
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.Fn panic .
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.Pp
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If control remains in
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.Fn panic ,
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an attempt is made to save an image of system memory on the
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configured dump device.
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.Pp
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If during the process of handling the panic,
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.Fn panic
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is called again
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.Pq from the filesystem synchronization routines, for example ,
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the system is rebooted immediately without synchronizing any filesystems.
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.Pp
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.Fn panic
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is meant to be used in situations where something unexpected has happened
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and it is difficult to recover the system to a stable state, or in
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situations where proceeding might make things worse, leading to data
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corruption and/or loss.
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It is not meant to be used in scenarios where the system could easily
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ignore and/or isolate the condition/subsystem and proceed.
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.Pp
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In general developers should try to reduce the number of
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.Fn panic
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calls in the kernel to improve stability.
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.Sh RETURN VALUES
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The
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.Fn panic
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function never returns.
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.Sh SEE ALSO
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.Xr sysctl 3 ,
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.Xr ddb 4 ,
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.Xr options 4 ,
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.Xr savecore 8 ,
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.Xr swapctl 8 ,
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.Xr sysctl 8
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