huge core.-files in /.ros after running ros

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Hey,

I am using Ros kinetic on a docker-image and I have the problem that the .ros folder gets to bigger whenever I run ros. At first I thought that log files might be the reason but after checking with rosclean, there are only log files of size 7M. In the folder are a lot of files named "core. " (see below), but I don't know whether it is save to delete them. Is this a ros problem or a problem with my docker image? Thanks in advance!

-rw------- 1 hermans studis  645353472 Dec  2 15:21 core.10464
-rw------- 1 hermans studis  458465280 Dec  3 15:55 core.10973
-rw------- 1 hermans studis  458526720 Dec  3 16:11 core.12356
-rw------- 1 hermans studis  721842176 Dec  2 14:41 core.15649
-rw------- 1 hermans studis  643411968 Dec  2 14:41 core.15655
-rw------- 1 hermans studis  645320704 Dec  3 14:37 core.17204
-rw------- 1 hermans studis  645341184 Dec  2 13:34 core.17387
-rw------- 1 hermans studis  946139136 Nov 26 16:41 core.18458
-rw------- 1 hermans studis  531349504 Dec  1 22:37 core.20002
-rw------- 1 hermans studis  640970752 Dec  2 13:37 core.20673
-rw------- 1 hermans studis  458534912 Dec  3 16:26 core.21079
-rw------- 1 hermans studis 1030107136 Nov 26 14:32 core.21259
-rw------- 1 hermans studis  645390336 Dec  2 14:07 core.21942
-rw------- 1 hermans studis  638570496 Nov 26 16:08 core.22841
-rw------- 1 hermans studis  519565312 Nov 26 16:08 core.22859
-rw------- 1 hermans studis  380657664 Dec  3 15:04 core.23051
-rw------- 1 hermans studis  645386240 Dec  2 14:43 core.23275
-rw------- 1 hermans studis  640897024 Dec  3 13:56 core.2329
-rw------- 1 hermans studis 1032560640 Nov 26 14:39 core.23928
-rw------- 1 hermans studis  645320704 Dec  2 13:23 core.23967
-rw------- 1 hermans studis  458567680 Dec  3 16:30 core.24036
-rw------- 1 hermans studis  972427264 Dec  1 22:26 core.2430
-rw------- 1 hermans studis  201175040 Dec  3 14:40 core.24860
-rw------- 1 hermans studis  972820480 Dec  3 14:21 core.24938
-rw------- 1 hermans studis  645390336 Dec  3 14:21 core.24943
-rw------- 1 hermans studis  638767104 Dec  1 22:58 core.25239
-rw------- 1 hermans studis  636870656 Dec  2 15:31 core.25244
-rw------- 1 hermans studis  575893504 Dec  3 16:00 core.26245
-rw------- 1 hermans studis  458199040 Dec  3 15:50 core.2632
-rw------- 1 hermans studis  458305536 Dec  3 16:34 core.26939
-rw------- 1 hermans studis 1027915776 Nov 26 13:21 core.27818
-rw------- 1 hermans studis 1020538880 Dec  2 15:34 core.28535
-rw------- 1 hermans studis  645332992 Dec  2 14:22 core.28990
-rw------- 1 hermans studis  645451776 Dec  2 15:38 core.31170
-rw------- 1 hermans studis  605876224 Dec  3 14:15 core.31763
-rw------- 1 hermans studis  193208320 Dec  3 14:13 core.31764
-rw------- 1 hermans studis 1031831552 Nov 26 13:32 core.4755
-rw------- 1 hermans studis 1020493824 ...