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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 October 5, 2021 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 the 55.Dv RLIMIT_CORE 56.Xr setrlimit 2 57limit. 58Files which would be larger than the limit are not created. 59.Pp 60With a large limit, a process that had mapped a very large, 61and perhaps sparsely populated, virtual memory region, could take 62a very long time to create core dumps. 63The system ignores all signals sent to a process writing a core file, except 64.Dv SIGKILL 65which terminates the writing and causes immediate exit of the process. 66The behavior of 67.Dv SIGKILL 68can be disabled by setting tunable 69.Xr sysctl 8 70variable 71.Va kern.core_dump_can_intr 72to zero. 73.Pp 74The name of the file is controlled via the 75.Xr sysctl 8 76variable 77.Va kern.corefile . 78The contents of this variable describes a filename to store 79the core image to. 80This filename can be absolute, or relative (which 81will resolve to the current working directory of the program 82generating it). 83.Pp 84The following format specifiers may be used in the 85.Va kern.corefile 86sysctl to insert additional information into the resulting core 87filename: 88.Bl -tag -width "1234567890" -compact -offset "12345" 89.It Em \&%H 90Machine hostname. 91.It Em \&%I 92An index starting at zero until the sysctl 93.Em debug.ncores 94is reached. 95This can be useful for limiting the number of corefiles 96generated by a particular process. 97.It Em \&%N 98process name. 99.It Em \&%P 100processes PID. 101.It Em \&%S 102signal during core. 103.It Em \&%U 104process UID. 105.El 106.Pp 107The name defaults to 108.Em \&%N.core , 109yielding the traditional 110.Fx 111behaviour. 112.Pp 113By default, a process that changes user or group credentials whether 114real or effective will not create a corefile. 115This behaviour can be 116changed to generate a core dump by setting the 117.Xr sysctl 8 118variable 119.Va kern.sugid_coredump 120to 1. 121.Pp 122Corefiles can be compressed by the kernel if the following item 123is included in the kernel configuration file: 124.Bl -tag -width "1234567890" -compact -offset "12345" 125.It options 126GZIO 127.El 128.Pp 129The following sysctl control core file compression: 130.Bl -tag -width "kern.compress_user_cores_level" -compact -offset "12345" 131.It Em kern.compress_user_cores 132Enable compression of user cores. 133A value of 1 configures 134.Xr gzip 1 135compression, 136and a value of 2 configures 137.Xr zstd 1 138compression. 139Compressed core files will have a suffix of 140.Ql .gz 141or 142.Ql .zst 143appended to their filenames depending on the selected format. 144.It Em kern.compress_user_cores_level 145Compression level. 146Defaults to 6. 147.El 148.Sh NOTES 149Corefiles are written with open file descriptor information as an ELF note. 150By default, file paths are packed to only use as much space as needed. 151However, file paths can change at any time, including during core dump, 152and this can result in truncated file descriptor data. 153.Pp 154All file descriptor information can be preserved by disabling packing. 155This potentially wastes up to PATH_MAX bytes per open fd. 156Packing is disabled with 157.Dl sysctl kern.coredump_pack_fileinfo=0 . 158.Pp 159Similarly, corefiles are written with vmmap information as an ELF note, which 160contains file paths. 161By default, they are packed to only use as much space as 162needed. 163By the same mechanism as for the open files note, these paths can also 164change at any time and result in a truncated note. 165.Pp 166All vmmap information can be preserved by disabling packing. 167Like the file information, this potentially wastes up to PATH_MAX bytes per 168mapped object. 169Packing is disabled with 170.Dl sysctl kern.coredump_pack_vmmapinfo=0 . 171.Sh EXAMPLES 172In order to store all core images in per-user private areas under 173.Pa /var/coredumps , 174the following 175.Xr sysctl 8 176command can be used: 177.Pp 178.Dl sysctl kern.corefile=/var/coredumps/\&%U/\&%N.core 179.Sh SEE ALSO 180.Xr gdb 1 , 181.Xr gzip 1 , 182.Xr kgdb 1 Pq Pa ports/devel/gdb , 183.Xr setrlimit 2 , 184.Xr sigaction 2 , 185.Xr sysctl 8 186.Sh HISTORY 187A 188.Nm 189file format appeared in 190.At v1 . 191