Since Omada 4 doesn’t contain java and mongodb with the installer package, you will need to install it manually first.
This is the guide for CentOS7
Java
yum install java-1.8.0-openjdk -yMongoDB
touch /etc/yum.repos.d/mongodb-org.repo
Paste the following into /etc/yum.repos.d/mongodb-org.repo
[mongodb-org-3.4]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/3.4/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-3.4.asc
yum install mongodb-org
systemctl enable mongod
systemctl start mongod