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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 February 13, 2018 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 71filename: 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 111The following sysctl control core file compression: 112.Bl -tag -width "kern.compress_user_cores_level" -compact -offset "12345" 113.It Em kern.compress_user_cores 114Enable compression of user cores. 115A value of 1 configures 116.Xr gzip 1 117compression, 118and a value of 2 configures 119.Xr zstd 1 120compression. 121Compressed core files will have a suffix of 122.Ql .gz 123or 124.Ql .zst 125appended to their filenames depending on the selected format. 126.It Em kern.compress_user_cores_level 127Compression level. 128Defaults to 6. 129.El 130.Sh NOTES 131Corefiles are written with open file descriptor information as an ELF note. 132By default, file paths are packed to only use as much space as needed. 133However, file paths can change at any time, including during core dump, 134and this can result in truncated file descriptor data. 135.Pp 136All file descriptor information can be preserved by disabling packing. 137This potentially wastes up to PATH_MAX bytes per open fd. 138Packing is disabled with 139.Dl sysctl kern.coredump_pack_fileinfo=0 . 140.Pp 141Similarly, corefiles are written with vmmap information as an ELF note, which 142contains file paths. 143By default, they are packed to only use as much space as 144needed. 145By the same mechanism as for the open files note, these paths can also 146change at any time and result in a truncated note. 147.Pp 148All vmmap information can be preserved by disabling packing. 149Like the file information, this potentially wastes up to PATH_MAX bytes per 150mapped object. 151Packing is disabled with 152.Dl sysctl kern.coredump_pack_vmmapinfo=0 . 153.Sh EXAMPLES 154In order to store all core images in per-user private areas under 155.Pa /var/coredumps , 156the following 157.Xr sysctl 8 158command can be used: 159.Pp 160.Dl sysctl kern.corefile=/var/coredumps/\&%U/\&%N.core 161.Sh SEE ALSO 162.Xr gdb 1 , 163.Xr gzip 1 , 164.Xr kgdb 1 , 165.Xr setrlimit 2 , 166.Xr sigaction 2 , 167.Xr sysctl 8 168.Sh HISTORY 169A 170.Nm 171file format appeared in 172.At v6 . 173