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161 lines
4.4 KiB
Groff
161 lines
4.4 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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.\" 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: @(#)swapon.8 8.1 (Berkeley) 6/5/93
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.\" $FreeBSD$
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.\"
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.Dd October 8, 2014
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.Dt DUMPON 8
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.Os
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.Sh NAME
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.Nm dumpon
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.Nd "specify a device for crash dumps"
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.Sh SYNOPSIS
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.Nm
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.Op Fl v
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.Ar special_file
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.Nm
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.Op Fl v
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.Cm off
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.Nm
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.Op Fl v
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.Fl l
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.Sh DESCRIPTION
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The
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.Nm
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utility is used to specify a device where the kernel can save a crash
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dump in the case of a panic.
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.Pp
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Calls to
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.Nm
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normally occur from the system multi-user initialization file
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.Pa /etc/rc ,
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controlled by the
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.Dq dumpdev
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variable in the boot time configuration file
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.Pa /etc/rc.conf .
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.Pp
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The default type of kernel crash dump is the mini crash dump.
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Mini crash dumps hold only memory pages in use by the kernel.
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Alternatively, full memory dumps can be enabled by setting the
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.Va debug.minidump
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.Xr sysctl 8
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variable to 0.
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.Pp
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For systems using full memory dumps, the size of the specified dump
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device must be at
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least the size of physical memory.
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Even though an additional 64 kB header is added to the dump, the BIOS for a
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platform typically holds back some memory, so it is not usually
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necessary to size the dump device larger than the actual amount of RAM
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available in the machine.
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Also, when using full memory dumps, the
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.Nm
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utility will refuse to enable a dump device which is smaller than the
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total amount of physical memory as reported by the
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.Va hw.physmem
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.Xr sysctl 8
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variable.
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.Pp
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The
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.Fl l
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flag causes
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.Nm
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to print the current dump device or _PATH_DEVNULL ("/dev/null") if no device is
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configured.
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.Pp
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The
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.Fl v
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flag causes
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.Nm
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to be verbose about its activity.
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.Sh IMPLEMENTATION NOTES
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Since a
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.Xr panic 9
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condition may occur in a situation
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where the kernel cannot trust its internal representation
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of the state of any given file system,
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one of the system swap devices,
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and
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.Em not
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a device containing a file system,
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should be used as the dump device.
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.Pp
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The
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.Nm
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utility operates by opening
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.Ar special_file
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and making a
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.Dv DIOCSKERNELDUMP
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.Xr ioctl 2
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request on it to save kernel crash dumps.
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If
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.Ar special_file
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is the text string:
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.Dq Li off ,
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.Nm
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performs a
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.Dv DIOCSKERNELDUMP
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.Xr ioctl 2
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on
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.Pa /dev/null
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and thus instructs the kernel not to save crash dumps.
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.Pp
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Since
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.Nm
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cannot be used during kernel initialization, the
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.Va dumpdev
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variable of
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.Xr loader 8
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must be used to enable dumps for system panics which occur
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during kernel initialization.
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.Sh FILES
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.Bl -tag -width "/dev/{ada,da}?s?b" -compact
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.It Pa /dev/{ada,da}?s?b
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standard swap areas
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.It Pa /etc/rc.conf
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boot-time system configuration
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.El
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.Sh SEE ALSO
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.Xr fstab 5 ,
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.Xr rc.conf 5 ,
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.Xr config 8 ,
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.Xr init 8 ,
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.Xr loader 8 ,
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.Xr rc 8 ,
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.Xr savecore 8 ,
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.Xr swapon 8 ,
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.Xr panic 9
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.Sh HISTORY
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The
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.Nm
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utility appeared in
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.Fx 2.1 .
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.Sh BUGS
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Because the file system layer is already dead by the time a crash dump
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is taken, it is not possible to send crash dumps directly to a file.
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