错误:软件包: ambari-server-2.7.0.0-897.x86_64(ambari )需要:postgresql-server＞=8.1

解决：

第一步安装postgresql-serve，且版本大于8.1

这里选择postgresql-serve的12版本

# 安装存储库 RPM：
sudo yum install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm
#按顺序安装如下包，包我已经放到这里，点开自取(http://114.55.237.251/postgresql/)
#安装libicu(postgresql需要该依赖)
rpm -ivh libicu-50.2-4.el7_7.x86_64.rpm 
#安装postgresql12-libs-12.6-1PGDG.rhel7.x86_64.rpm
rpm -ivh postgresql12-libs-12.6-1PGDG.rhel7.x86_64.rpm 
#安装postgresql12-12.6-1PGDG.rhel7.x86_64.rpm
rpm -ivh postgresql12-12.6-1PGDG.rhel7.x86_64.rpm 
#安装postgresql12-server-12.6-1PGDG.rhel7.x86_64.rpm
rpm -ivh postgresql12-server-12.6-1PGDG.rhel7.x86_64.rpm 
#最后安装ambari-serve即可
yum -y install ambari-serve