b5cadc643e
This can be disabled by sysctl kern.core_dump_can_intr Reported and tested by: pho Reviewed by: imp, markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D32313
191 lines
6.0 KiB
Groff
191 lines
6.0 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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.\" @(#)core.5 8.3 (Berkeley) 12/11/93
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.\" $FreeBSD$
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.\"
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.Dd October 5, 2021
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.Dt CORE 5
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.Os
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.Sh NAME
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.Nm core
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.Nd memory image file format
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.Sh SYNOPSIS
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.In sys/param.h
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.Sh DESCRIPTION
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A small number of signals which cause abnormal termination of a process
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also cause a record of the process's in-core state to be written
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to disk for later examination by one of the available debuggers.
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(See
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.Xr sigaction 2 . )
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This memory image is written to a file named by default
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.Nm programname.core
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in the working directory;
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provided the terminated process had write permission in the directory,
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and provided the abnormality did not cause
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a system crash.
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(In this event, the decision to save the core file is arbitrary, see
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.Xr savecore 8 . )
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.Pp
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The maximum size of a core file is limited by the
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.Dv RLIMIT_CORE
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.Xr setrlimit 2
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limit.
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Files which would be larger than the limit are not created.
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.Pp
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With a large limit, a process that had mapped a very large,
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and perhaps sparsely populated, virtual memory region, could take
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a very long time to create core dumps.
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The system ignores all signals sent to a process writing a core file, except
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.Dv SIGKILL
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which terminates the writing and causes immediate exit of the process.
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The behavior of
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.Dv SIGKILL
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can be disabled by setting tunable
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.Xr sysctl 8
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variable
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.Va kern.core_dump_can_intr
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to zero.
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.Pp
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The name of the file is controlled via the
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.Xr sysctl 8
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variable
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.Va kern.corefile .
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The contents of this variable describes a filename to store
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the core image to.
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This filename can be absolute, or relative (which
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will resolve to the current working directory of the program
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generating it).
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.Pp
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The following format specifiers may be used in the
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.Va kern.corefile
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sysctl to insert additional information into the resulting core
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filename:
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.Bl -tag -width "1234567890" -compact -offset "12345"
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.It Em \&%H
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Machine hostname.
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.It Em \&%I
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An index starting at zero until the sysctl
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.Em debug.ncores
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is reached.
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This can be useful for limiting the number of corefiles
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generated by a particular process.
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.It Em \&%N
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process name.
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.It Em \&%P
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processes PID.
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.It Em \&%S
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signal during core.
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.It Em \&%U
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process UID.
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.El
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.Pp
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The name defaults to
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.Em \&%N.core ,
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yielding the traditional
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.Fx
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behaviour.
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.Pp
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By default, a process that changes user or group credentials whether
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real or effective will not create a corefile.
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This behaviour can be
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changed to generate a core dump by setting the
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.Xr sysctl 8
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variable
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.Va kern.sugid_coredump
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to 1.
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.Pp
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Corefiles can be compressed by the kernel if the following item
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is included in the kernel configuration file:
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.Bl -tag -width "1234567890" -compact -offset "12345"
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.It options
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GZIO
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.El
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.Pp
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The following sysctl control core file compression:
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.Bl -tag -width "kern.compress_user_cores_level" -compact -offset "12345"
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.It Em kern.compress_user_cores
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Enable compression of user cores.
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A value of 1 configures
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.Xr gzip 1
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compression,
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and a value of 2 configures
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.Xr zstd 1
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compression.
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Compressed core files will have a suffix of
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.Ql .gz
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or
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.Ql .zst
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appended to their filenames depending on the selected format.
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.It Em kern.compress_user_cores_level
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Compression level.
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Defaults to 6.
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.El
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.Sh NOTES
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Corefiles are written with open file descriptor information as an ELF note.
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By default, file paths are packed to only use as much space as needed.
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However, file paths can change at any time, including during core dump,
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and this can result in truncated file descriptor data.
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.Pp
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All file descriptor information can be preserved by disabling packing.
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This potentially wastes up to PATH_MAX bytes per open fd.
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Packing is disabled with
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.Dl sysctl kern.coredump_pack_fileinfo=0 .
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.Pp
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Similarly, corefiles are written with vmmap information as an ELF note, which
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contains file paths.
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By default, they are packed to only use as much space as
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needed.
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By the same mechanism as for the open files note, these paths can also
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change at any time and result in a truncated note.
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.Pp
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All vmmap information can be preserved by disabling packing.
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Like the file information, this potentially wastes up to PATH_MAX bytes per
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mapped object.
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Packing is disabled with
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.Dl sysctl kern.coredump_pack_vmmapinfo=0 .
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.Sh EXAMPLES
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In order to store all core images in per-user private areas under
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.Pa /var/coredumps ,
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the following
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.Xr sysctl 8
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command can be used:
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.Pp
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.Dl sysctl kern.corefile=/var/coredumps/\&%U/\&%N.core
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.Sh SEE ALSO
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.Xr gdb 1 ,
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.Xr gzip 1 ,
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.Xr kgdb 1 ,
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.Xr setrlimit 2 ,
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.Xr sigaction 2 ,
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.Xr sysctl 8
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.Sh HISTORY
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A
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.Nm
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file format appeared in
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.At v1 .
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