Q:

Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension. - Redmine installation on Debian 7

I follow installation instructions from here:  
http://www.redmine.org/projects/redmine/wiki/HowTo_Install_Redmine_2_integrated_with_Gitolite_2_on_Debian_Wheezy_with_Apache_and_Phusion_Passenger 
This is my output:  
root@projects:~# sudo -i -u redmine -H sh -c "bundle install --without development test postgresql sqlite"
Your Gemfile lists the gem redcarpet (~> 2.3.0) more than once.
You should probably keep only one of them.
While it's not a problem now, it could cause errors if you change the version of just one of them later.
Updating https://github.com/jbox-web/gitolite-rugged.git
Updating https://github.com/jbox-web/grack.git
Fetching gem metadata from https://rubygems.org/........
Fetching version metadata from https://rubygems.org/..
Resolving dependencies...
Using rake 10.4.2
Using RedCloth 4.2.9
Using i18n 0.6.11
Using multi_json 1.10.1
Using activesupport 3.2.21
Using builder 3.0.4
Using activemodel 3.2.21
Using erubis 2.7.0
Using journey 1.0.4
Using rack 1.4.5
Using rack-cache 1.2
Using rack-test 0.6.3
Using hike 1.2.3
Using tilt 1.4.1
Using sprockets 2.2.3
Using actionpack 3.2.21
Using mime-types 1.25.1
Using polyglot 0.3.5
Using treetop 1.4.15
Using mail 2.5.4
Using actionmailer 3.2.21
Using arel 3.0.3
Using tzinfo 0.3.43
Using activerecord 3.2.21
Using activeresource 3.2.21
Using asciidoctor 1.5.2
Using bundler 1.7.13
Using coderay 1.1.0
Using creole 0.5.0
Using dalli 2.7.2
Using posix-spawn 0.3.9
Using github-markup 1.3.1
Using gitlab-grack 2.0.0.pre from https://github.com/jbox-web/grack.git (at fix_rails3)
Using gratr19 0.4.4.1

Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

        /usr/bin/ruby1.9.1 extconf.rb
checking for cmake... no
ERROR: CMake is required to build Rugged.
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=/usr/bin/ruby1.9.1

Gem files will remain installed in /tmp/bundler20150209-10079-1stz4fv/rugged-0.21.4/gems/rugged-0.21.4 for inspection.
Results logged to /tmp/bundler20150209-10079-1stz4fv/rugged-0.21.4/gems/rugged-0.21.4/ext/rugged/gem_make.out
An error occurred while installing rugged (0.21.4), and Bundler cannot continue.
Make sure that `gem install rugged -v '0.21.4'` succeeds before bundling.
root@projects:~#  

any ideas ?! how to fix

A:

You need to install cmake 
sudo apt-get install cmake

