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[root@localhost config]# gem install bundler

Fetching: bundler-2.0.2.gem (100%)

ERROR:  Error installing bundler:

bundler requires Ruby version >= 2.3.0.

解决方法：

使用rvm升级ruby

1.安装rvm

# curl -sSL https://get.rvm.io | bash -s stable

# source /usr/local/rvm/scripts/rvm

2.查看rvm库中已知的ruby版本

# rvm list known

3.安装一个ruby版本

# rvm install 2.6

4.使用一个ruby版本

[root@localhost config]# rvm use 2.6.3

Using /usr/local/rvm/gems/ruby-2.6.3

5.设置默认版本

[root@localhost config]# rvm remove 2.3.0

ruby-2.3.0 - #already gone

Using /usr/local/rvm/gems/ruby-2.6.3

6.确认最终版本

[root@localhost config]# ruby --version

ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-linux]

再次执行gem install bundler命令

[root@localhost config]# gem install bundler

Fetching bundler-2.0.2.gem

Successfully installed bundler-2.0.2

Parsing documentation for bundler-2.0.2

Installing ri documentation for bundler-2.0.2

Done installing documentation for bundler after 4 seconds

1 gem installed

 成功了！