9d3ecb7e62
Add format capability to core file names to include signal that generated the core. This can help various validation workflows where all cores should not be considered equally (SIGQUIT is often intentional and not an error unlike SIGSEGV or SIGBUS) Submitted by: David Leimbach (leimy2k@gmail.com) Reviewed by: markj MFC after: 1 week Relnotes: sysctl kern.corefile can now include the signal number Sponsored by: Dell EMC Isilon Differential Revision: https://reviews.freebsd.org/D20970
175 lines
5.5 KiB
Groff
175 lines
5.5 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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.\" @(#)core.5 8.3 (Berkeley) 12/11/93
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.\" $FreeBSD$
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.\"
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.Dd February 13, 2018
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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
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.Xr setrlimit 2 .
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Files which would be larger than the limit are not created.
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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 v6 .
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