Question

On Ubuntu 12.04, open a new text file and write:

#include <stdlib.h>

int main()
{
    abort();
    return 0;
}

Now run:

g++ yourfile.cpp

Then run the executable, which will core dump:

./a.out

Now check the mtime of the file:

-rw-r----- 1 xxxxx xxxxx 228K 2012-10-01 19:20:20.752136399 -0500 core

Now run the executable again:

./a.out

Now check the mtime again:

-rw-r----- 1 xxxxx xxxxx 228K 2012-10-01 19:20:20.752136399 -0500 core

It’s the same! Why doesn’t a fresh core dump overwrite the old one? When rebuilding this causes gdb to complain the core is older than the executable.

Just to be sure it wasn’t a permissions problem, I tried this in a fresh directory in /tmp and ran chmod -R 777 **/* inside. Running the executable twice still didn’t produce a new core O_o Also, ulimit -c reports 800000000, more than enough for a core this size.

I also tried running a clean bash with env - bash --noprofile --norc and still running the binary doesn’t update the mtime of the core unless I delete it first.

Answer 1

If you refer to https://bugs.launchpad.net/ubuntu/+source/apport/+bug/160999 this is a bug in Ubuntu using O_EXCL to open the file, preventing it from overwriting an existing core.