Add Zammad, Elasticsearch & epel-release RPM repos and install RPM

Install-zammad-CentOS

sudo yum -y install epel-release wget
sudo wget -O /etc/yum.repos.d/zammad.repo https://dl.packager.io/srv/zammad/zammad/stable/installer/el/7.repo

echo "[elasticsearch-5.x]
name=Elasticsearch repository for 5.x packages
baseurl=https://artifacts.elastic.co/packages/5.x/yum
gpgcheck=1
gpgkey=https://artifacts.elastic.co/GPG-KEY-elasticsearch
enabled=1
autorefresh=1
type=rpm-md" | sudo tee /etc/yum.repos.d/elasticsearch.repo

sudo yum -y install java elasticsearch
sudo systemctl daemon-reload
sudo systemctl enable elasticsearch
sudo systemctl start elasticsearch

sudo yum -y install zammad

nginx
/etc/nginx/conf.d/zammad.conf

server {
    listen 80;

    # replace 'localhost' with your fqdn if you want to use zammad from remote
    server_name localhost;
    
You can manage the Zammad services manually:
Zammad
sudo systemctl status zammad
sudo systemctl stop zammad
sudo systemctl start zammad
sudo systemctl restart zammad

Only web application server
sudo systemctl status zammad-web
sudo systemctl stop zammad-web
sudo systemctl start zammad-web
sudo systemctl restart zammad-web

Only worker process
sudo systemctl status zammad-worker
sudo systemctl stop zammad-worker
sudo systemctl zammad-worker
sudo systemctl restart zammad-worker

Only websocket server
sudo systemctl status zammad-websocket
sudo systemctl stop zammad-websocket
sudo systemctl start zammad-websocket
sudo systemctl restart zammad-websocket