Set Permanently ulimit -n / open files in ubuntu

set ulimit

# available limit
user@ubuntu:~$ ulimit -n
1024

# To increase the available limit to say 65535
user@ubuntu:~$ sudo nano /etc/sysctl.conf

# add the following line to it
fs.file-max = 1024576

sudo vim /etc/security/limits.conf

# add following lines to it
* soft     nproc          1024576    
* hard     nproc          1024576   
* soft     nofile         1024576   
* hard     nofile         1024576
root soft     nproc          1024576    
root hard     nproc          1024576   
root soft     nofile         1024576   
root hard     nofile         1024576

# edit the following file
user@ubuntu:~$ sudo nano /etc/pam.d/common-session

# add this line to it
session required pam_limits.so

# run this to refresh with new config
user@ubuntu:~$ sudo sysctl -p

# logout and login and try the following command
user@ubuntu:~$ ulimit -n
1024576