How to increase the number of open files allowed for Nginx.

Introduction

When reviewing the Nginx error log, you may see errors like the one below. 

socket() failed (24: Too many open files)

This can be resolved by increasing the open files Nginx is allowed to have.

Procedure

On a server using Systemd to manage services, do the following:

mkdir -vp /etc/systemd/system/nginx.service.d

Create a file with a .conf extension:

touch /etc/systemd/system/nginx.service.d/override.conf

Add the following:

[Service]
LimitNOFILE=4096

Reload Systemd daemon with:

systemctl daemon-reload

Then restart Nginx with the following:

/scripts/restartsrv_nginx --hard

Verify the changes using the following command:

grep 'open file' /proc/$(pgrep -u root -f 'nginx: master')/limits