redis requires ruby version 2.2.2的解决方案
今天在做Redis的Cluster集群的时候，在执行gem install redis时，提示如下错误：
gem install redis
ERROR: Error installing redis:
redis requires Ruby version >= 2.2.2.
CentOS7 yum库中ruby的版本支持到 2.0.0，可gem 安装redis需要最低是2.2.2，采用rvm来更新ruby：
1、安装RVM（具体命令可以查看官网，Ruby官网地址 和 Ruby官网安装教程）：
//具体RVM安装命令地址：http://rvm.io/
[root@linux ~]# gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 7D2BAF1CF37B13E2069D6956105BD0E739499BDB
[root@linux ~]# curl -sSL https://get.rvm.io | bash -s stable
[root@linux ~]# find / -name rvm -print
/usr/local/rvm
/usr/local/rvm/src/rvm
/usr/local/rvm/src/rvm/bin/rvm
/usr/local/rvm/src/rvm/lib/rvm
/usr/local/rvm/src/rvm/scripts/rvm
/usr/local/rvm/bin/rvm
/usr/local/rvm/lib/rvm
/usr/local/rvm/scripts/rvm
[root@linux ~]# source /usr/local/rvm/scripts/rvm
2、查看rvm库中已知的ruby版本：
[root@linux ~]# rvm list known
MRI Rubies
[ruby-]1.8.6[-p420]
[ruby-]1.8.7[-head] # security released on head
[ruby-]1.9.1[-p431]
[ruby-]1.9.2[-p330]
[ruby-]1.9.3[-p551]
[ruby-]2.0.0[-p648]
[ruby-]2.1[.10]
[ruby-]2.2[.7]
[ruby-]2.3[.4]
[ruby-]2.4[.1]
ruby-head
….
3、安装一个ruby版本：
[root@linux ~]# rvm install 2.4.1
Searching for binary rubies, this might take some time.
Found remote file https://rvm_io.global.ssl.fastly.net/binaries/centos/7/x86_64/ruby-2.4.1.tar.bz2
Checking requirements for centos.
Requirements installation successful.
ruby-2.4.1 - #configure
ruby-2.4.1 - #download
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 14.1M 100 14.1M 0 0 97k 0 0:02:27 0:02:27 --:--:-- 159k
No checksum for downloaded archive, recording checksum in user configuration.
ruby-2.4.1 - #validate archive
ruby-2.4.1 - #extract
ruby-2.4.1 - #validate binary
ruby-2.4.1 - #setup
ruby-2.4.1 - #gemset created /usr/local/rvm/gems/ruby-2.4.1@global
ruby-2.4.1 - #importing gemset /usr/local/rvm/gemsets/global.gems..............................
ruby-2.4.1 - #generating global wrappers........
ruby-2.4.1 - #gemset created /usr/local/rvm/gems/ruby-2.4.1
ruby-2.4.1 - #importing gemsetfile /usr/local/rvm/gemsets/default.gems evaluated to empty gem list
ruby-2.4.1 - #generating default wrappers........
4、使用一个ruby版本：
[root@linux ~]# rvm use 2.4.1
Using /usr/local/rvm/gems/ruby-2.4.1
5、设置默认版本：(设置ruby2.4.1为默认的ruby，因为还安装有1.8.3)
[root@linux ~]# rvm use 2.4.1 --default
Using /usr/local/rvm/gems/ruby-2.4.1
6、卸载一个已知版本：
[root@linux ~]# rvm remove 2.3.4
7、查看ruby版本：
[root@linux ~]# ruby --version
ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux]
8、安装redis：
[root@linux ~]# gem install redis
Fetching: redis-4.0.1.gem (100%)
Successfully installed redis-4.0.1
Parsing documentation for redis-4.0.1
Installing ri documentation for redis-4.0.1
Done installing documentation for redis after 3 seconds
1 gem installed
