看看安装过程：
lijg@lijg-pc ~ $ rvm install 1.8.6
Installing Ruby from source to: /home/lijg/.rvm/rubies/ruby-1.8.6-p420, this may take a while depending on your cpu(s)...
ruby-1.8.6-p420 - #fetching
ruby-1.8.6-p420 - #downloading ruby-1.8.6-p420, this may take a while depending on your connection...
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 3892k 100 3892k 0 0 12897 0 0:05:09 0:05:09 --:--:-- 15427
ruby-1.8.6-p420 - #extracting ruby-1.8.6-p420 to /home/lijg/.rvm/src/ruby-1.8.6-p420
ruby-1.8.6-p420 - #extracted to /home/lijg/.rvm/src/ruby-1.8.6-p420
ruby-1.8.6-p420 - #configuring
ruby-1.8.6-p420 - #compiling
ruby-1.8.6-p420 - #installing
Removing old Rubygems files...
Installing rubygems-1.3.7 for ruby-1.8.6-p420 ...
Installation of rubygems completed successfully.
ruby-1.8.6-p420 - adjusting #shebangs for (gem irb erb ri rdoc testrb rake).
ruby-1.8.6-p420 - #importing default gemsets (/home/lijg/.rvm/gemsets/)
Install of ruby-1.8.6-p420 - #complete
看看rvm中安装的ruby版本，默认使用的版本是如何实现的
cd ~/.rvm/rubies
ll
total 20
drwxr-xr-x 5 lijg lijg 4096 2012-04-28 09:31 ./
drwxr-xr-x 23 lijg lijg 4096 2011-08-24 14:38 ../
lrwxrwxrwx 1 lijg lijg 38 2012-04-17 14:59 default -> /home/lijg/.rvm/rubies/ruby-1.8.7-p352/
drwxr-xr-x 5 lijg lijg 4096 2012-04-28 09:31 ruby-1.8.6-p420/
drwxr-xr-x 5 lijg lijg 4096 2012-04-16 19:28 ruby-1.8.7-p352/
drwxr-xr-x 6 lijg lijg 4096 2011-08-24 14:42 ruby-1.9.2-p290/