这是什么。我首先做了：
rvm get stable
rvm install ruby-2.2.2
没有成交。它向我展示了以下内容：
$ rvm install ruby-2.2.2
Searching for binary rubies, this might take some time.
No binary rubies available for: ubuntu/14.04/i386/ruby-2.2.2.
Continuing with compilation. Please read 'rvm help mount' to get more information on binary rubies.
Checking requirements for ubuntu.
Requirements installation successful.
Installing Ruby from source to: /home/myuser/.rvm/rubies/ruby-2.2.2, this may take a while depending on your cpu(s)...
ruby-2.2.2 - #downloading ruby-2.2.2, this may take a while depending on your connection...
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 0 0 0 0 0 0 0 --:--:-- 0:00:19 --:--:-- 0Warning: Transient problem: timeout Will retry in 2 seconds. 3 retries left.
0 0 0 0 0 0 0 0 --:--:-- 0:00:19 --:--:-- 0Warning: Transient problem: timeout Will retry in 2 seconds. 2 retries left.
0 0 0 0 0 0 0 0 --:--:-- 0:00:19 --:--:-- 0Warning: Transient problem: timeout Will retry in 2 seconds. 1 retries left.
0 0 0 0 0 0 0 0 --:--:-- 0:00:19 --:--:-- 0curl: (6) Could not resolve host: cache.ruby-lang.org
There was an error(6).
Checking fallback: http://ftp.ruby-lang.org/pub/ruby/2.2/ruby-2.2.2.tar.bz2
Checking fallback: http://www.mirrorservice.org/sites/ftp.ruby-lang.org/pub/ruby/2.2/ruby-2.2.2.tar.bz2
No fallback URL could be found, try increasing timeout with:
echo "export rvm_max_time_flag=20" >> ~/.rvmrc
There has been an error fetching the ruby interpreter. Halting the installation.
我增加了超时时间：
echo "export rvm_max_time_flag=20" >> ~/.rvmrc
但没有交易。我也这样rvm get head做了，并且重新做了一遍，超时时间更长，但仍然没有好处。
我该怎么做才能在 ubuntu 上正确安装 ruby-2.2.2？