Unable to create a core file for my crashed program

Question

I am using Ubuntu 12.04 LTS. I wrote a simple program as follows to create crash

// null.c
#include<stdio.h>

int main()
{
   int *p = NULL;
   int k=*p;
   printf("%d",sizeof(0));
   return 0;
}

Now I run with "gcc -g null.c" and then "./a.out" and the output is as expected.

Segmentation fault (core dumped)

Now I want to see the core dump file using gdb. I did the following things

1. I checked the current directory, there is no core dump file
2. I tried tried to change the /proc/sys/kernel/core_pattern with the content "core.%e.%p". But i am not able to write into the file. It is saying "Fsync Failed".
3. I used the "sudo vi /proc/sys/kernel/core_pattern". Still can't write into the file.

I want to create the core dump in my current directory. What to do now?

Answer 1

Your real question appears to be not "where is my core dump", but rather "how can I modify /proc/sys/kernel/core_pattern".

sudo bash -c 'echo core.%e.%p > /proc/sys/kernel/core_pattern'

should do the trick.

Answer 2

You need to adjust your core dump size limit with following command:

ulimit -S -c maximum-core-dump-size

The the value is given in Kb.

Answer 3

you do not need to use core pattern. its just dumps in that format %e.%p

what you need to do is #ulimit -c unlimited

and check #ulimit -a

and confirm if core file size is set properly. You will get the core as core.pid after that.

Answer 4

My understanding is that using ulimit is not permanent, i.e. if you reboot then the limit goes back to 0. To have unlimited permanent, you need to change /etc/security/limits.conf. Similarly for core pattern etc, change /etc/sysctl.conf.