Question

For any gem that has dependencies, I get the following (with the names changed as applicable):

Attempt 1:

sudo gem install mojombo-jekyll -s http://gems.github.com/
ERROR:  Error installing mojombo-jekyll:
        mojombo-jekyll requires RedCloth (= 4.1.0, runtime)

Attempt 2:

sudo gem install mojombo-jekyll -s http://gems.github.com/ -y
INFO:  `gem install -y` is now default and will be removed
INFO:  use --ignore-dependencies to install only the gems you list
ERROR:  Error installing mojombo-jekyll:
        mojombo-jekyll requires RedCloth (= 4.1.0, runtime)

Attempt 3:

sudo gem install mojombo-jekyll -s http://gems.github.com/ --include-dependencies
INFO:  `gem install -y` is now default and will be removed
INFO:  use --ignore-dependencies to install only the gems you list
ERROR:  Error installing mojombo-jekyll:
        mojombo-jekyll requires RedCloth (= 4.1.0, runtime)

Answer 1

The problem is not dependency related but source related.
If you specify the ‘-s’ option, rubygems will only use that source or sources.

sudo gem install mojombo-jekyll -s http://gems.github.com/ -s http://gems.rubyforge.org

This will tell rubygems to use both rubyforge and github.
Most people tend to take the approach of adding the gem source to their environment instead of doing it manually each time.