CentOS7.5 mongoDB4.0 install
$ cat /etc/redhat-release
CentOS Linux release 7.5.1804 (Core)
$ arch
x86_64
$ sudo vi /etc/yum.repos.d/mongodb-org-4.0.repo
[mongodb-org-4.0]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/4.0/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-4.0.asc
sudo yum install -y mongodb-org