Error while installing json gem 'mkmf.rb can't find header files for ruby'

For context, it on a remote server which has a firewall. I'm setting up my environment through a proxy. I have ruby 1.8.7. When I try to gem install..

sudo gem install --http-proxy : json

I get the following error:

Building native extensions.  This could take a while...
ERROR:  Error installing json:
        ERROR: Failed to build gem native extension.

/usr/bin/ruby extconf.rb
mkmf.rb can't find header files for ruby at /usr/lib/ruby/ruby.h

Gem files will remain installed in /usr/lib64/ruby/gems/1.8/gems/json-1.8.1 for inspection.
Results logged to /usr/lib64/ruby/gems/1.8/gems/json-1.8.1/ext/json/ext/generator/gem_make.out

Since I was unsure what the problem is, I googled and found these

-
gem install: Failed to build gem native extension (can't find header files) - the instructions here seem to be specific to the gem being installed.

-
How to install json gem - Failed to build gem native extension This seems to be slightly different error.

Any hints? Thanks!

Modern era update, as stated by mimoralea:


In case that you are using ruby 2.0 or 2.2 (thanks @patrick-davey).

sudo apt-get install ruby2.0-dev
sudo apt-get install ruby2.2-dev
sudo apt-get install ruby2.3-dev

or, generic way:

sudo apt-get install ruby-dev

or

sudo apt-get install ruby`ruby -e 'puts RUBY_VERSION[/\d+\.\d+/]'`-dev

The first link you’ve posted is exactly your case: there is no ruby development environment installed. Development env is needed to compile ruby extensions, which are mostly written in C. Proxy has nothing to do with the problem: everything is downloaded fine, just compilation fails.

I would suggest you to install ruby-dev (ruby-devel for rpm-based distros) package onto you target machine.

gcc package might be needed as well.

Try:

$ sudo apt-get install ruby-dev

Or, for Redhat distro:

$ sudo yum install ruby-devel

Or, for [open]SuSE:

$ sudo zypper install ruby-devel

Stack Overflow Q#20559255, score: 941