6026dcd7ca
This works similarly to the existing gzip compression support, but zstd is typically faster and gives better compression ratios. Support for this functionality must be configured by adding ZSTDIO to one's kernel configuration file. dumpon(8)'s new -Z option is used to configure zstd compression for kernel dumps. savecore(8) now recognizes and saves zstd-compressed kernel dumps with a .zst extension. Submitted by: cem (original version) Relnotes: yes Sponsored by: Dell EMC Isilon Differential Revision: https://reviews.freebsd.org/D13101, https://reviews.freebsd.org/D13633
313 lines
7.5 KiB
Groff
313 lines
7.5 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. 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 February 13, 2018
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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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.Op Fl k Ar public_key_file
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.Op Fl z
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.Op Fl Z
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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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and
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.Dq dumppubkey
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variables 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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.Op Fl k Ar public_key_file
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flag causes
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.Nm
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to generate a one-time key for kernel crash dump encryption.
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The key will be replaced by a new one when the
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.Nm
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utility is run again.
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The key is encrypted using
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.Ar public_key_file .
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This process is sandboxed using
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.Xr capsicum 4 .
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Both plain and encrypted keys are sent to the kernel using
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.Dv DIOCSKERNELDUMP
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.Xr ioctl 2 .
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A user can specify the
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.Ar public_key_file
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in the
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.Dq dumppubkey
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variable defined in
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.Pa /etc/rc.conf
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for use with the
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.Pa /etc/rc.d/dumpon
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.Xr rc 8
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script.
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This flag requires a kernel compiled with the
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.Dv EKCD
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kernel option.
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.Pp
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The
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.Fl z
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and
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.Fl Z
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options configure the kernel to compress the dump before writing it to
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the dump device.
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This reduces the amount of space required for the dump and accelerates
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recovery with
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.Xr savecore 8
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since less data needs to be copied from the dump device.
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When compression is enabled, the
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.Nm
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utility will not verify that the dump device is sufficiently large for a full
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dump.
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The
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.Fl z
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and
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.Fl Z
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options cause the dump to be written in
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.Xr gzip 1
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and
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.Xr zstd 1
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format, respectively.
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These flags require a kernel compiled with the
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.Dv GZIO
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or
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.Dv ZSTDIO
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kernel options.
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.Pp
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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 EXAMPLES
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In order to generate an RSA private key a user can use the
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.Xr genrsa 1
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tool:
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.Pp
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.Dl # openssl genrsa -out private.pem 4096
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.Pp
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A public key can be extracted from the private key using the
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.Xr rsa 1
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tool:
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.Pp
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.Dl # openssl rsa -in private.pem -out public.pem -pubout
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.Pp
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Once the RSA keys are created the private key should be moved to a safe place.
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Now
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.Pa public.pem
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can be used by
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.Nm
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to configure encrypted kernel crash dumps:
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.Pp
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.Dl # dumpon -k public.pem /dev/ada0s1b
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.Pp
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It is recommended to test if the kernel saves encrypted crash dumps using the
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current configuration.
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The easiest way to do that is to cause a kernel panic using the
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.Xr ddb 4
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debugger:
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.Pp
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.Dl # sysctl debug.kdb.panic=1
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.Pp
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In the debugger the following commands should be typed to write a core dump and
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reboot:
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.Pp
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.Dl db> call doadump(0)
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.Dl db> reset
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.Pp
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After reboot
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.Xr savecore 8
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should be able to save the core dump in the core directory which is
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.Pa /var/crash
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by default:
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.Pp
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.Dl # savecore /var/crash /dev/ada0s1b
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.Pp
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Three files should be created in the core directory:
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.Pa info.# ,
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.Pa key.#
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and
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.Pa vmcore_encrypted.#
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where
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.Dq #
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is the number of the last core dump saved by
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.Xr savecore 8 .
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The
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.Pa vmcore_encrypted.#
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can be decrypted using the
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.Xr decryptcore 8
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utility:
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.Pp
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.Dl # decryptcore -p private.pem -k key.# -e vmcore_encrypted.# -c vmcore.#
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.Pp
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or shorter:
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.Pp
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.Dl # decryptcore -p private.pem -n #
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.Pp
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The
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.Pa vmcore.#
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can be now examined using
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.Xr kgdb 1 :
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.Pp
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.Dl # kgdb /usr/obj/sys/GENERIC/kernel.debug vmcore.#
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.Pp
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or shorter:
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.Pp
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.Dl # kgdb -n # /usr/obj/sys/GENERIC/kernel.debug
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.Pp
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The core was decrypted properly if
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.Xr kgdb 1
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does not print any errors.
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.Sh SEE ALSO
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.Xr gzip 1 ,
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.Xr kgdb 1 ,
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.Xr zstd 1 ,
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.Xr ddb 4 ,
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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 decryptcore 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 2.0.5 .
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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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.Pp
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It is currently not possible to configure both compression and encryption.
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The encrypted dump format assumes that the kernel dump size is a multiple
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of the cipher block size, which may not be true when the dump is compressed.
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