Redis安装ruby报错：Error installing redis: redis requires Ruby version...
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.
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/
# gpg2 --keyserver hkp://keys.gnupg.net --recv-keys D39DC0E3
# curl -sSL https://get.rvm.io | bash -s stable
# 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
# source /usr/local/rvm/scripts/rvm
2、查看rvm库中已知的ruby版本：
# rvm list known
MRI Rubies
1.8.6[-p420]
1.8.7[-head] # security released on head
1.9.1[-p431]
1.9.2[-p330]
1.9.3[-p551]
2.0.0[-p648]
2.1[.10]
2.2[.7]
2.3[.4]
2.4[.1]
ruby-head
….
3、安装一个ruby版本：
# 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 % XferdAverage Speed Time Time TimeCurrent
DloadUpload Total Spent LeftSpeed
100 14.1M100 14.1M 0 0 97k 00:02:270:02:27 --:--:--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：
# 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)
# rvm use 2.4.1 --default
Using /usr/local/rvm/gems/ruby-2.4.1
6、卸载一个已知版本：
# rvm remove 2.3.4
7、查看ruby版本：
# ruby --version
ruby 2.4.1p111 (2017-03-22 revision 58053)
8、安装redis：
# 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
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