1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)core.5 8.3 (Berkeley) 12/11/93 29.\" $FreeBSD$ 30.\" 31.Dd March 8, 2015 32.Dt CORE 5 33.Os 34.Sh NAME 35.Nm core 36.Nd memory image file format 37.Sh SYNOPSIS 38.In sys/param.h 39.Sh DESCRIPTION 40A small number of signals which cause abnormal termination of a process 41also cause a record of the process's in-core state to be written 42to disk for later examination by one of the available debuggers. 43(See 44.Xr sigaction 2 . ) 45This memory image is written to a file named by default 46.Nm programname.core 47in the working directory; 48provided the terminated process had write permission in the directory, 49and provided the abnormality did not cause 50a system crash. 51(In this event, the decision to save the core file is arbitrary, see 52.Xr savecore 8 . ) 53.Pp 54The maximum size of a core file is limited by 55.Xr setrlimit 2 . 56Files which would be larger than the limit are not created. 57.Pp 58The name of the file is controlled via the 59.Xr sysctl 8 60variable 61.Va kern.corefile . 62The contents of this variable describes a filename to store 63the core image to. 64This filename can be absolute, or relative (which 65will resolve to the current working directory of the program 66generating it). 67.Pp 68The following format specifiers may be used in the 69.Va kern.corefile 70sysctl to insert additional information into the resulting core file 71name: 72.Bl -tag -width "1234567890" -compact -offset "12345" 73.It Em \&%H 74Machine hostname. 75.It Em \&%I 76An index starting at zero until the sysctl 77.Em debug.ncores 78is reached. 79This can be useful for limiting the number of corefiles 80generated by a particular process. 81.It Em \&%N 82process name. 83.It Em \&%P 84processes PID. 85.It Em \&%U 86process UID. 87.El 88.Pp 89The name defaults to 90.Em \&%N.core , 91yielding the traditional 92.Fx 93behaviour. 94.Pp 95By default, a process that changes user or group credentials whether 96real or effective will not create a corefile. 97This behaviour can be 98changed to generate a core dump by setting the 99.Xr sysctl 8 100variable 101.Va kern.sugid_coredump 102to 1. 103.Pp 104Corefiles can be compressed by the kernel if the following item 105is included in the kernel configuration file: 106.Bl -tag -width "1234567890" -compact -offset "12345" 107.It options 108GZIO 109.El 110.Pp 111When the GZIO option is included, the following sysctls control whether core 112files will be compressed: 113.Bl -tag -width "kern.compress_user_cores_gzlevel" -compact -offset "12345" 114.It Em kern.compress_user_cores_gzlevel 115Gzip compression level. 116Defaults to 6. 117.It Em kern.compress_user_cores 118Actually compress user cores. 119Compressed core files will have a suffix of 120.Ql .gz 121appended to them. 122.El 123.Sh EXAMPLES 124In order to store all core images in per-user private areas under 125.Pa /var/coredumps , 126the following 127.Xr sysctl 8 128command can be used: 129.Pp 130.Dl sysctl kern.corefile=/var/coredumps/\&%U/\&%N.core 131.Sh SEE ALSO 132.Xr gdb 1 , 133.Xr kgdb 1 , 134.Xr setrlimit 2 , 135.Xr sigaction 2 , 136.Xr sysctl 8 137.Sh HISTORY 138A 139.Nm 140file format appeared in 141.At v6 . 142