Isso funcionou para mim no Ubuntu 18.04 :
1) Edite /data/repos/mhservers/etc/pam.d/common-session
e adicione:
session optional pam_systemd.so
2) Edite /etc/security/limits.d/somename.conf
e defina
someuser soft nofile 1024000
someuser hard nofile 1024000
3) UID de pesquisa usando id -u someuser
4) Execute systemctl restart user@[UID].service
Para verificar que someuser
pode executar systemctl --user show somesvr.service | grep NOFILE