I am totally new in database administration, i have 3 virtual servers on conetos 7 2 cpu 4 ram 50 gb hdd, i tried several times to install greenplum, but it was not successful, plsease share some notes or guide of installation
There is no specific information about your troubles, that you're experiencing. I can say that there were differences compare to Ubuntu 18.04 installation. Main problem and difference was that there were lack of necessary python libs in GreenPlum distribution to work correctly during cluster initialisation:
сd ~
sudo yum install -y python-devel wget tar
wget https://github.com/giampaolo/psutil/archive/refs/tags/release-5.4.8.tar.gz -O psutil.tar.gz
tar -xvf psutil.tar.gz
cd ~/psutil-release-5.4.8 && sudo /usr/local/greenplum-db/ext/python/bin/python setup.py install
cd ~
wget https://github.com/yaml/pyyaml/archive/refs/tags/5.3.1.tar.gz
tar -xzf 5.3.1.tar.gz
cd pyyaml-5.3.1
sudo /usr/local/greenplum-db/ext/python/bin/python setup.py install
That fixed cluster init for me with my CentOS 7 + GP 6.22.2. Without psutil you can't initialise cluster, without pyyaml you can't use PXF, so far as I remember. So far as I remember there is no such problem with 6.19. Everything else was just by manual. I experienced some troubles using default gp_interconnect_type=udpifc, and tcp worked better, but I'm researching it right now.
You should start with this manual: https://docs.vmware.com/en/VMware-Greenplum/6/greenplum-database/install_guide-prep_os.html and go further through this document.
UPD: Be aware! CentOS + GreenPlum has the problem with UDP interconnect. Issue is discussed here: https://github.com/greenplum-db/gpdb/issues/12961#issuecomment-1345793255 You can workaround this bug by switching parameter to gp_interconnect_type from udpifc to tcp using gpconfig utility. So if you'll have more than 1000 segments combined or you gonna run heavy queries with more than 1000 slices, you better try to switch to Ubuntu 18.04 LTS to use udpifc interconnect, that can handle more than 1000 segments and slices.