出现的问题：

[root@localhost ~]# gem install redis

Fetching: redis-4.0.1.gem (100%)

ERROR: Error installing redis:

redis requires Ruby version >= 2.2.2.

原因:ruby版本太低，要求2.2.2版本+

解决：安装rbuy高版本

需要用rvm 来安装ruby

[root@localhost ~]# gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3

gpg: keyring `/root/.gnupg/secring.gpg' created

gpg: requesting key D39DC0E3 from hkp server keys.gnupg.net

gpg: /root/.gnupg/trustdb.gpg: trustdb created

gpg: key D39DC0E3: public key "Michal Papis (RVM signing) " imported

gpg: no ultimately trusted keys found

gpg: Total number processed: 1

gpg: imported: 1 (RSA: 1)

[root@localhost ~]# \curl -sSL https://get.rvm.io | bash -s stable

Downloading https://github.com/rvm/rvm/archive/1.29.3.tar.gz

curl: (52) Empty reply from server

Could not download 'https://github.com/rvm/rvm/archive/1.29.3.tar.gz'.

curl returned status '52'.

Downloading https://bitbucket.org/mpapis/rvm/get/1.29.3.tar.gz

Downloading https://bitbucket.org/mpapis/rvm/downloads/1.29.3.tar.gz.asc

gpg: Signature made Mon 11 Sep 2017 04:59:29 AM CST using RSA key ID BF04FF17

gpg: Good signature from "Michal Papis (RVM signing) "

gpg: aka "Michal Papis "

gpg: aka "[jpeg image of size 5015]"

gpg: WARNING: This key is not certified with a trusted signature!

gpg: There is no indication that the signature belongs to the owner.

Primary key fingerprint: 409B 6B17 96C2 7546 2A17 0311 3804 BB82 D39D C0E3

Subkey fingerprint: 62C9 E5F4 DA30 0D94 AC36 166B E206 C29F BF04 FF17

GPG verified '/usr/local/rvm/archives/rvm-1.29.3.tgz'

Creating group 'rvm'

Installing RVM to /usr/local/rvm/

Installation of RVM in /usr/local/rvm/ is almost complete:

* First you need to add all users that will be using rvm to 'rvm' group,

and logout - login again, anyone using rvm will be operating with `umask u=rwx,g=rwx,o=rx`.

* To start using RVM you need to run `source /etc/profile.d/rvm.sh`

in all your open shell windows, in rare cases you need to reopen all shell windows.

[root@localhost ~]# source /etc/profile.d/rvm.sh

[root@localhost ~]# rvm -v

rvm 1.29.3 (latest) by Michal Papis, Piotr Kuczynski, Wayne E. Seguin [https://rvm.io]

查询rvm库中ruby的版本

[root@localhost ~]# 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

# for forks use: rvm install ruby-head- --url https://github.com/github/ruby.git --branch 2.2

# JRuby

jruby-1.6[.8]

jruby-1.7[.27]

jruby[-9.1.13.0]

jruby-head

# Rubinius

rbx-1[.4.3]

rbx-2.3[.0]

rbx-2.4[.1]

rbx-2[.5.8]

rbx-3[.84]

rbx-head

# Opal

opal

# Minimalistic ruby implementation - ISO 30170:2012

mruby-1.0.0

mruby-1.1.0

mruby-1.2.0

mruby-1[.3.0]

mruby[-head]

# Ruby Enterprise Edition

ree-1.8.6

ree[-1.8.7][-2012.02]

# Topaz

topaz

# MagLev

maglev[-head]

maglev-1.0.0

# Mac OS X Snow Leopard Or Newer

macruby-0.10

macruby-0.11

macruby[-0.12]

macruby-nightly

macruby-head

# IronRuby

ironruby[-1.1.3]

ironruby-head

安装最新的2.4版本ruby

[root@localhost ~]# rvm install 2.4

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.

Installing requirements for centos.

Installing required packages: patch, autoconf, automake, bison, bzip2, libffi-devel, libtool, patch, readline-devel, sqlite-devel, zlib-devel, li...............

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 117k 0 0:02:02 0:02:02 --:--:-- 121k

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........

切换使用2.4版本ruby

[root@localhost ~]# rvm use 2.4

Using /usr/local/rvm/gems/ruby-2.4.1

移除2.0.0 版本ruby

[root@localhost ~]# rvm remove 2.0.0

ruby-2.0.0-p648 - #already gone

Using /usr/local/rvm/gems/ruby-2.4.1

验证ruby版本

[root@localhost ~]# ruby -v

ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux]