1.必须内核版本高于 2.80 ，通过 uname -r 命令查看你当前的内核版本
2.sudo yum update
遇到问题nitscripts conflicts with redhat-release-server-7.0-1.el7.x86_64
删除 rpm -e redhat-release-server-7.0-1.el7.x86_64 --nodeps 解决；
3.等待系统下载更新一堆rpm包，中间有确认的直接Y掉即可
4.yum install mono-complete 出现询问直接Y
5.mono -V ——查看安装运行环境版本信息，注意是大写的V字母 注意空格，不行了手敲
Mono JIT compiler version 6.8.0.123 (tarball Mon Feb 22 21:52:52 UTC 2021)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
TLS: __thread
SIGSEGV: altstack
Notifications: epoll
Architecture: amd64
Disabled: none
Misc: softdebug
Interpreter: yes
LLVM: supported, not enabled.
Suspend: hybrid
GC: sgen (concurrent by default)
6.