Redmine

update, I was able to get nokogiri, but still getting the same error....

I need some help...

I have been following these instructions:

I having an issue with this step:
Install dependencies using the Gem bundler¶
This step will look at the dependencies specified in the Gemfile:
% cd /var/www/redmine
% bundle install

When I run the command, I get this error:

[fit54@u ~]$ cd /var/www/redmine
[fit54@u redmine]$ bundle install
The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x64-mingw32, x86-mswin32. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x64-mingw32 x86-mswin32`.
/usr/share/gems/gems/psych-2.0.0/lib/psych.rb:98: warning: already initialized constant Psych::VERSION
/usr/share/ruby/psych.rb:98: warning: previous definition of VERSION was here
/usr/share/gems/gems/psych-2.0.0/lib/psych.rb:101: warning: already initialized constant Psych::LIBYAML_VERSION
/usr/share/ruby/psych.rb:101: warning: previous definition of LIBYAML_VERSION was here
Fetching gem metadata from https://rubygems.org/..........
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies....
Using rake 12.3.1
Using i18n 0.7.0
Using minitest 5.11.3
Using thread_safe 0.3.6
Using tzinfo 1.2.5
Using activesupport 4.2.8
Using builder 3.2.3
Using erubis 2.7.0
Using mini_portile2 2.1.0
Fetching nokogiri 1.6.8.1
Installing nokogiri 1.6.8.1 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory: /home/fit54/.gem/ruby/gems/nokogiri-1.6.8.1/ext/nokogiri
/usr/bin/ruby -r ./siteconf20180406-9964-oibzlr.rb extconf.rb
--use-system-libraries
mkmf.rb can't find header files for ruby at /usr/share/include/ruby.h

extconf failed, exit code 1

Gem files will remain installed in /home/fit54/.gem/ruby/gems/nokogiri-1.6.8.1
for inspection.
Results logged to
/home/fit54/.gem/ruby/extensions/x86_64-linux/nokogiri-1.6.8.1/gem_make.out

An error occurred while installing nokogiri (1.6.8.1), and Bundler
cannot continue.
Make sure that `gem install nokogiri -v '1.6.8.1'` succeeds before bundling.

In Gemfile:
rails was resolved to 4.2.8, which depends on
actionmailer was resolved to 4.2.8, which depends on
actionpack was resolved to 4.2.8, which depends on
actionview was resolved to 4.2.8, which depends on
rails-dom-testing was resolved to 1.0.9, which depends on
nokogiri

Please let me know what other information I need to provide or what help can be given to me to help resolve this issue.