Gem Install Cannot Find a Header File

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

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

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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

gem install cannot find a header file

The answer to this question was answered by the gem author via email, but I'd like to share the solution.

sudo env ARCHFLAGS="-arch x86_64" gem install talib_ruby -- --with-talib-include=/opt/local/var/macports/software/ta-lib/0.4.0_0/opt/local/include/ta-lib  --with-talib-lib=/opt/local/var/macports/software/ta-lib/0.4.0_0/opt/local/lib

It is important to note that this gem is also not compatible with Ruby 1.9.2. From what the error list generated, it had some issues with the definition of struct RObject (fill in Object with String, Array, etc), which I traced to the ruby.h header file. If you'd like to use this gem, you can install rvm and then type

rvm install ruby-1.8.7 --with-readline-dir=/opt/local

From there, simply follow the guidance from the gem author with the input listed above.

UPDATE: the gem author has made talib_ruby compatible with 1.9.x so there is no longer a need to install 1.8.7

gem install: Failed to build gem native extension (can't find header files)

For those who may be confused by the accepted answer, as I was, you also need to have the ruby headers installed [ruby-devel].

The article that saved my hide is here.

And this is the revised solution (note that I'm on Fedora 13):

yum -y install gcc mysql-devel ruby-devel rubygems
gem install -y mysql -- --with-mysql-config=/usr/bin/mysql_config

For Debian, and other distributions using Debian style packaging the ruby development headers are installed by:

sudo apt-get install ruby-dev

For Ubuntu the ruby development headers are installed by:

sudo apt-get install ruby-all-dev

If you are using a earlier version of ruby (such as 2.2), then you will need to run:

sudo apt-get install ruby2.2-dev

(where 2.2 is your desired Ruby version)

Error: Failed to build gem native extension (can't find header files for ruby.h)

Well I suspect you actually need ruby2.4-dev if you're using ruby 2.4. But I'd recommend not using system ruby and installing gems globally with sudo in the first place. Using a ruby environment manager such as rbenv is the best way to avoid dependency hell. Here's a good overview of the available options: http://kgrz.io/programmers-guide-to-choosing-ruby-version-manager.html

Failing installing pg gem, mkmf.rb can't find header files for ruby (Mac OSX 10.6.5)

Generally the gem bundles for Postgres want to know where pg_config is hiding so they can ask about the Postgres installation.

Use locate pg_config to see if your Mac knows where it's hiding.

I installed a copy of Postgres using mappstack, so my Mac says there's a copy at:

/Applications/mappstack-1.2-3/postgresql/bin/pg_config

and another at:

/Library/PostgreSQL/9.0/bin/pg_config

I don't remember installing the one at /Library/PostgreSQL/9.0, so it might have been preinstalled by Snow Leopard, or I did it when under the influence of too much work, possibly using the Postgres installer from EnterpriseDB.

Once you've found the location of pg_config try adding that directory to the start of your PATH and then rerun the gem install.
Or use:

export SQL_PATH=/Library/PostgreSQL/9.0
gem install pg -- --with-pg-config=$SQL_PATH/bin/pg_config

and try installing. If either of those work you're done. Otherwise...

The next thing the installers might want are access to the Postgres headers, so you look in the parent of the bin directories, and see if you can find an include directory.

After that, look in that directory for a lib directory. Once you know those locations you should have all you need to set your environment variables to let the installer complete. You'll need to read the README or INSTALL file of the installer and see what needs to be set up. You'll be configuring:

export include_dir=$SQL_PATH/include/
export     lib_dir=$SQL_PATH/lib/
gem install pg -- --with-pgsql-include-dir=$include_dir --with-pgsql-lib-dir=$lib_dir

Hopefully that'll all help. I have Rails 3 and my Postgres running fine, using the mappstack Postgres and the EnterpriseDB versions, so the above info should get you there.

Can't find header files while running bundle install

Paths suggest you are using a Mac, right? Maybe this answer solves your problem?

gem install mysql failure in Snow Leopard

Error looks the same. Accepted answer said that "Installing the Xcode that's bundled with the Snow Leopard fixed the problem."

Can't find header files for Ruby on SUSE?

For those with similar issues I got this working by.

Uninsalling ruby and rvm
Building zlib from source with the shared option

./configure --shared
make 
make install

I did the same for Ruby and that worked.

I could not get any RPM, Zypper, RVM installers to install properly. In each case they all seemed to have issues with zlib ?

Docker for Mac - mkmf.rb can't find header files for ruby

For Xcode 11 on macOS 10.14, this can happen even after installing Xcode and installing command-line tools and accepting the license with

sudo xcode-select --install
sudo xcodebuild -license accept

The issue is that Xcode 11 ships the macOS 10.15 SDK which includes headers for ruby2.6, but not for macOS 10.14's ruby2.3. You can verify that this is your problem by running

ruby -rrbconfig -e 'puts RbConfig::CONFIG["rubyhdrdir"]'

which on macOS 10.14 with Xcode 11 prints the non-existent path

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/include/ruby-2.3.0

However, Xcode 11 installs a macOS 10.14 SDK within /Library/Developer/CommandLineTools/SDKs/MacOS10.14.sdk. It isn't necessary to pollute the system directories by installing the old header files as suggested in other answers. Instead, by selecting that SDK, the appropriate ruby2.3 headers will be found:

sudo xcode-select --switch /Library/Developer/CommandLineTools
ruby -rrbconfig -e 'puts RbConfig::CONFIG["rubyhdrdir"]'

This should now correctly print

/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/include/ruby-2.3.0

Likewise, gem install should work while that SDK is selected.

To switch back to using the current Xcode 11 SDK, use

sudo xcode-select --switch /Applications/Xcode.app

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