Bug#815020: breaks coredump handling for systems without systemd-coredump

[Josh Triplett]

severity 815020 grave
thanks

On Wed, 17 Feb 2016 21:25:43 -0300 Felipe Sateler <fsateler at debian.org> wrote:
> On 17 February 2016 at 21:03, Wouter Verhelst <wouter at debian.org> wrote:
>> An alternative solution would be that systemd-sysv shipped with a unit
>> which would set the core_pattern back to default, which could be
>> overridden or disabled by a unit shipped by a unit shipped with
>> systemd-coredump? That would be less surprising -- I have to say I spent
>> a long time tracking down what happened.
> 
> I think the bigger problem is setting the default core rlimit, not the
> core_pattern. The /bin/false core_pattern is being set because the
> default rlimit was raised, otherwise you would get core files
> everywhere on your system. In turn, the rlimit was raised because now
> systemd-coredump respects the limit (previously it would ignore it and
> save larger than allowed dumps).

No, the core_pattern is a problem as well.  Default out-of-the-box
behavior with current systemd:

/tmp$ ulimit -c
unlimited
/tmp$ cat >crash.c <<EOF
> int main(void) { return *(int *)0; }
> EOF
/tmp$ gcc crash.c -o crash
/tmp$ ./crash
Segmentation fault (core dumped)
(139) /tmp$ ls -l core
ls: cannot access 'core': No such file or directory

This does not work as a default configuration.  The default core_pattern
must remain the kernel default "core".  It seems perfectly reasonable
for systemd-coredump to override that if installed, but in the absence
of that, setting "ulimit -c unlimited" must generate core files.  The
sysadmin should *not* have to manually fix core_pattern to retain the
expected behavior.

Given that the default core_pattern must remain the kernel default
"core", then the default "ulimit -c" must remain 0.

I don't see anything wrong with systemd-coredump installing a
systemd.conf.d file that sets DefaultLimitCORE; the sysadmin can still
easily override that with their own systemd.conf.d file.  The package
description should explicitly mention the behavior change caused by
installation.  The package should also explicitly note that installing
systemd-coredump will not enable coredumps for existing processes, and
that the sysadmin may wish to either restart existing processes or
manually enable coredumps for them using "prlimit -c unlimited --pid
PID".

- Josh Triplett