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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 August 2, 2020 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 \&%S 86signal during core. 87.It Em \&%U 88process UID. 89.El 90.Pp 91The name defaults to 92.Em \&%N.core , 93yielding the traditional 94.Fx 95behaviour. 96.Pp 97By default, a process that changes user or group credentials whether 98real or effective will not create a corefile. 99This behaviour can be 100changed to generate a core dump by setting the 101.Xr sysctl 8 102variable 103.Va kern.sugid_coredump 104to 1. 105.Pp 106Corefiles can be compressed by the kernel if the following item 107is included in the kernel configuration file: 108.Bl -tag -width "1234567890" -compact -offset "12345" 109.It options 110GZIO 111.El 112.Pp 113The following sysctl control core file compression: 114.Bl -tag -width "kern.compress_user_cores_level" -compact -offset "12345" 115.It Em kern.compress_user_cores 116Enable compression of user cores. 117A value of 1 configures 118.Xr gzip 1 119compression, 120and a value of 2 configures 121.Xr zstd 1 122compression. 123Compressed core files will have a suffix of 124.Ql .gz 125or 126.Ql .zst 127appended to their filenames depending on the selected format. 128.It Em kern.compress_user_cores_level 129Compression level. 130Defaults to 6. 131.El 132.Sh NOTES 133Corefiles are written with open file descriptor information as an ELF note. 134By default, file paths are packed to only use as much space as needed. 135However, file paths can change at any time, including during core dump, 136and this can result in truncated file descriptor data. 137.Pp 138All file descriptor information can be preserved by disabling packing. 139This potentially wastes up to PATH_MAX bytes per open fd. 140Packing is disabled with 141.Dl sysctl kern.coredump_pack_fileinfo=0 . 142.Pp 143Similarly, corefiles are written with vmmap information as an ELF note, which 144contains file paths. 145By default, they are packed to only use as much space as 146needed. 147By the same mechanism as for the open files note, these paths can also 148change at any time and result in a truncated note. 149.Pp 150All vmmap information can be preserved by disabling packing. 151Like the file information, this potentially wastes up to PATH_MAX bytes per 152mapped object. 153Packing is disabled with 154.Dl sysctl kern.coredump_pack_vmmapinfo=0 . 155.Sh EXAMPLES 156In order to store all core images in per-user private areas under 157.Pa /var/coredumps , 158the following 159.Xr sysctl 8 160command can be used: 161.Pp 162.Dl sysctl kern.corefile=/var/coredumps/\&%U/\&%N.core 163.Sh SEE ALSO 164.Xr gdb 1 , 165.Xr gzip 1 , 166.Xr kgdb 1 , 167.Xr setrlimit 2 , 168.Xr sigaction 2 , 169.Xr sysctl 8 170.Sh HISTORY 171A 172.Nm 173file format appeared in 174.At v1 . 175