[CentOS] another bizarre thing...

Tue Aug 6 11:27:54 UTC 2019
Warren Young <warren at etr-usa.com>

On Aug 5, 2019, at 6:57 PM, Fred Smith <fredex at fcshome.stoneham.ma.us> wrote:
> no core file (yes, ulimit is configured)

That’s nowhere near sufficient.  To restore classic core file dumps on CentOS 7, you must:

1. Remove Red Hat’s ABRT system, which wants to catch all of this and handle it directly.  Say something like “sudo yum remove abrt*”

2. Override the default sysctl telling where core dumps land by writing this file, /etc/sysctl.d/10-core.conf:

    kernel.core_pattern = /tmp/core-%e-%p
    kernel.core_uses_pid = 1
    fs.suid_dumpable = 2

Then apply those settings with “sudo sysctl —system”.

I don’t remember what the default is, which this overrides, but I definitely didn’t want it.

You can choose any pattern you like, just remember what permissions the service runs under, because that’s the permission needed by the process that actually dumps the core to make the file hit the disk.  That’s why I chose /tmp in this example: anyone can write there.

3. Raise the limits by writing the following to /etc/security/limits.d/10-core.conf:

    * hard core unlimited
    * soft core unlimited

If this is what you meant by “ulimit,” then great, but I suspect you actually meant “ulimit -c unlimited”, but I believe until you do the above, the ulimit CLI app can have no effect.  You have to log out and back in to make this take effect.

Once the above is done, “ulimit -c unlimited” can take effect, but it’s of no value at all in conjunction with systemd services, for example, since those don’t run under a standard shell, so your .bash_profile and such aren’t even exec’d.

4. If your program is launched via systemd, then you must edit /etc/systemd/system.conf and set


then say “sudo systemctl daemon-reeexec”

Case matters; “Core” won’t work.  Ask me how I know. :)

5. If you have a systemd unit file for your service, you have to set a related value in there as well:


You need both because #4 sets the system-wide cap, while this sets the per-service value, which can go no higher than the system cap.

6. Restart the service to apply the above two changes.

Yes, it really is that difficult to enable classic core dumps on CentOS 7.  You’re welcome. :)