sudo -i -u postgres pg_dump zabbix > /tmp/zabbix_db.sql
yum install http://repo.zabbix.com/zabbix/3.4/rhel/7/x86_64/zabbix-release-3.4-1.el7.centos.noarch.rpm
yum clean all
systemctl stop zabbix-server.service
systemctl stop zabbix-agent.service
systemctl stop postgresql-9.6.service
yum update