New versions of systemd (like in Ubuntu 16.04) are able to configure pid Cgroups (ulimit -u via Cgroups) using TasksMax.

Check the commit implementing TaksMax.

Author: Lennart Poettering <lennart@poettering.net>
Date:   Fri Nov 13 19:28:32 2015 +0100

    core: enable TasksMax= for all services by default, and set it to 512

    Also, enable TasksAccounting= for all services by default, too.

    See:

    http://lists.freedesktop.org/archives/systemd-devel/2015-November/035006.html

But not we’ve got silly defaults:

$ systemctl show -p TasksMax docker
TasksMax=512

$ systemctl show -p TasksMax mysql
TasksMax=512

So if you use Docker or MySQL most likely you are going to have trouble without really putting load on your server.

Just set TasksMax for your service.

TasksMax=infinity

Feel free to configure that setting fitting you load :)

Viel Spaß

Erkan \o/

Update 1: There will be an update for Debian/Ubuntu setting TaskMax=infinity as default.

Update 2: With version 230 there is a new default \o/ KillUserProcesses=yes. Check it out yourself and cry :(