# maximum capability of system
user@ubuntu:~$ cat /proc/sys/fs/file-max
708444
# available limit
user@ubuntu:~$ ulimit -n
1024
# To increase the available limit to say 200000
user@ubuntu:~$ sudo vim /etc/sysctl.conf
# add the following line to it
fs.file-max = 200000
# run this to refresh with new config
user@ubuntu:~$ sudo sysctl -p
# edit the following file
user@ubuntu:~$ sudo vim /etc/security/limits.conf
# add following lines to it
* soft nproc 200000
* hard nproc 200000
* soft nofile 200000
* hard nofile 200000
root soft nproc 200000
root hard nproc 200000
root soft nofile 200000
root hard nofile 200000
# edit the following file
user@ubuntu:~$ sudo vim /etc/pam.d/common-session
# add this line to it
session required pam_limits.so
# logout and login and try the following command
user@ubuntu:~$ ulimit -n
200000
# now you can increase no.of.connections per Nginx worker
# in Nginx main config /etc/nginx/nginx.conf
worker_connections 200000;