I recently upgraded from MacOS Catalina to Big Sur beta and the first thing I noticed was that my dev environment was broken. My website was setup locally using Jekyll and when I tried to run ‘bundle exec jekyll serve’, I got this error:
Could not find eventmachine-1.2.7 in any of the sources
Run `bundle install` to install missing gems.
And running ‘bundle install’ didn’t seem to solve it (even with sudo), it showed this error:
An error occurred while installing eventmachine (1.2.7), and Bundler cannot continue.
Make sure that `gem install eventmachine -v '1.2.7' --source 'https://rubygems.org/'` succeeds
before bundling.
Running gem install eventmachine also returns an error, and the mkmf.log file showed an error with ruby:
"xcrun clang -o conftest -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/universal-darwin20 -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby/backward -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -D_DARWIN_UNLIMITED_SELECT -D_REENTRANT -g -Os -pipe -DHAVE_GCC_ATOMIC_BUILTINS -DUSE_FFI_CLOSURE_ALLOC conftest.c -L. -L/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib -L. -L/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.Internal.sdk/usr/local/lib -lruby.2.6 "
In file included from conftest.c:1:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby.h:33:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby/ruby.h:24:10: fatal error: 'ruby/config.h' file not found
#include "ruby/config.h"
^~~~~~~~~~~~~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby/ruby.h:24:10: note: did not find header 'config.h' in framework 'ruby' (loaded from '/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks')
1 error generated.
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: int main(int argc, char **argv)
4: {
5: return 0;
6: }
/* end */
package configuration for openssl is not found
And at the time of writing this post, Homebrew doesn’t support MacOS 11 Big Sur, so “brew install rbenv ruby-build” doesn’t work.

How to fix command line tools (CLT) in MacOS Big Sur:
I did some search online, and found this answer on stack overflow (Which involves installing Xcode 12 beta);
So follow these steps to install rbenv. You need xcode installed for step 4. Also, I updated the steps to match my use case;
git clone https://github.com/rbenv/rbenv.git ~/.rbenv
cd ~/.rbenv && src/configure && make -C src
- Add
~/.rbenv/bin
to your $PATH for access to the rbenv command-line utility. see: https://github.com/rbenv/rbenv#basic-github-checkout xcode-select --switch /Applications/Xcode-beta.app/Contents/Developer
- Now in your Jekyll project's root, you should be able to run
bundle install
and it should install all missing dependencies.
Now ‘bundle exec jekyll serve’ should start your server.
I hope this helps someone ✌🏾