cannot raise the limit of max open files for other users than root

[s7r <s7r@sky-ip.org>]

Hello,

Running Debian Stretch here.

I modified /etc/security/limits.conf with limits for soft/hard nofile to
10000 for * (any user), root and my username. Also added session
requried to /etc/pam.d/common-session* files.

Only for root ulimit -Hn or -Sn shown the correct number. For my
username it did not work until I edited /etc/systemd/user.conf and
/etc/systemd/system.conf with the number of max open files I am willing
to allow for this user.

Is this a bug or expected behavior? Why doesn't it work from editing
/etc/security/limits.conf?

Thank you.