this is how to set maximum number of open file and maximum number of processess on systemd startup script. for example you want give nginx process nofile 20000 and nproc unlimited.
edit nginx.service file
#vi /etc/systemd/system/multi-user.target.wants/nginx.service
add these into [Service] section
LimitNOFILE=20000 LimitNPROC=infinity
reload the systemd script daemon
#systemctl daemon-reload
finally, restart nginx service, and you’re done.
#systemctl restart nginx.service