WCOREDUMP(status) seems to always return true even though the feature is turned off

Question

Somehow, it looks like WCOREDUMP(status) always tells me that a core file was created.

I fork() and when I get a SIGCHLD signal, I use waitpid(...&status...);.

Then when I use WIFSIGNALED(status), I see the expected segmentation fault with WTERMSIG(status) (code 11) and somehow I also get true when I call WCOREDUMP(status).

However, by default Ubuntu is setup to not generate a core dump file. How come WCOREDUMP() still returns true? (unless the core file is saved somewhere else than in the current directory?)

Answer 1

I found out that the core dump file is generated by the kernel and sent to the apport application. The information is found in man 5 core which has a section:

Piping core dumps to a program

This program is defined in /proc/sys/kernel/core_pattern and on most Ubuntu systems, looks like this:

|/usr/share/apport/apport %p %s %c %P

This means pipe the core dump data to application apport, which in turn may decide to send the data to a file if

1. the program that crashed is not one which is to be reported to Ubuntu; and
2. the ulimit of your process is larger than zero.

So, as far as the kernel is concerned, the core dump was generated and thus WCOREDUMP() returning true is sensible.