Try:

yum group list

To see if yum can find the Development Tools under Available Groups. If it fails, try:

yum clean all
yum group list

And see if it can find it. If it still fails, you might not have the correct mirrors enabled to resolve it.

try the clean command again and then:

yum --disablerepo=\* --enablerepo=base,updates group list

If you can find it. Great! Install with:

yum --disablerepo=\* --enablerepo=base,updates groupinstall "Development Tools"

If not so, can you give us the output of:

yum repolist all

EDIT:

Thank you for the output.

I found an article which state the following: "To install the CentOS Development tools, you will need to be able to connect to your Virtual Server using SSH, and work as the root user."

Try switching to user "root" (if you don't know the root login credentials, you can try sudo su. sudo also might work but I see you already have tried that...) and running the above commands.

Lastly, you can try and enable these "sources" repos:

• CentOS-7 - Base Sources
• CentOS-7 - Extras Sources
• CentOS-7 - Updates Sources

And than running yum update followed by groupinstall.

Let me know if that doesn't work. Good luck!

I was getting an error with the repositories as well. The following resolved it for me

$ sudo su
# vi /etc/yum.repos.d/CentOS-Media.repo

I changed enabled=1 to enabled=0 and :wq

I create a small shell script:

#!/bin/sh

echo "installing essential tools and libraries for CentOS" ;

yum -y groupinstall "Development Tools" ;
yum -y groupinstall "Development Libraries" ;
yum -y install gcc-g++ git-core wget links zip unzip unrar ;
yum -y install mysql-server mysql-client mysql-devel ;
yum -y install openssl ;
yum -y install cmake ;

echo "Done."

I ran the script and everything installed successfully. Then, I was able to use yum to install clamav and everything else I wanted to install so far.

You don't need to have make before any installation. rpm operates on packages - so all stuff inside a package.rpm is already compiled (except *-devel.rpm etc.). Just do as you mentioned, download needed rpm's, copy to destination machine and do rpm -ihv yourstuff.rpm (and yes, remember about dependencies).