安装cassandra，
[重点]下载orcle java8
保证java version是稳定的 “1.8.0”
否则运行cassandra时会产生报错：
[0.001s][error][logging] Error opening log file ‘/var/log/cassandra/gc.log’: Permission denied
[0.001s][error][logging] Initialization of output ‘file=/var/log/cassandra/gc.log’ using options ‘filecount=10,filesize=10485760’ failed.
Invalid -Xlog option ‘-Xlog:gc=info,heap*=trace,age*=debug,safepoint=info,promotion*=trace:file=/var/log/cassandra/gc.log:time,uptime,pid,tid,level:filecount=10,filesize=10485760’, see error log for details.
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
安装步骤：
1.将Cassandra的Apache存储库添加到中/etc/apt/sources.list.d/cassandra.sources.list，例如，以获取最新的3.11版本：
echo “deb https://downloads.apache.org/cassandra/debian 311x main” | sudo tee -a /etc/apt/sources.list.d/cassandra.sources.list
2.添加Apache Cassandra存储库密钥：
curl https://downloads.apache.org/cassandra/KEYS | sudo apt-key add -
3.更新存储库：
sudo apt-get update
4.安装Cassandra：
sudo apt-get install cassandra
5 运行cassandra