如何用sudo gem安装rails？

Question

$ gem install rails

ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /home/user/.rvm/rubies/ruby-2.4.1/lib/ruby/gems/2.4.0 directory.

$ sudo gem install rails
sudo: gem: command not found
$ gem -v
2.6.12

为什么sudo gem install rails导致命令未找到？
现在如何安装rails？

user@debian:~$ su root
Password: 
root@debian:/home/user# gem install rails
bash: gem: command not found

Answer 1

您可以使用root用户

su root
gem install rails