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

Question

I updated XCode on my Mac and since then when starting Docker using docker-sync-stack start I get this error message:

mkmf.rb can\'t find header         


        

Answer 1

As @bdorfman said in his comment, the Ruby headers are no longer included as of Xcode 11 build but they seem to try to make a new build for this as soon as possible (?): https://discuss.circleci.com/t/xcode-11-gm-seed-2-released/32505/12.

What worked for me was to use rbenv like @bdorfman said:

rbenv install 2.6.4
rbenv global 2.6.4
eval "$(rbenv init -)"

But with the extra step of adding docker-sync to your new ruby version. Since after you change the ruby version (for example)

$ ruby -v
ruby 2.6.4p104 (2019-08-28 revision 67798) [x86_64-darwin18]

And then running gem list:

$ gem list
bigdecimal (default: 1.4.1)
bundler (default: 1.17.2)
cmath (default: 1.0.0)
csv (default: 3.0.9)
date (default: 2.0.0)
dbm (default: 1.0.0)
did_you_mean (1.3.0)
e2mmap (default: 0.1.0)
etc (default: 1.0.1)
fcntl (default: 1.0.0)
fiddle (default: 1.0.0)
fileutils (default: 1.1.0)
forwardable (default: 1.2.0)
io-console (default: 0.4.7)
ipaddr (default: 1.2.2)
irb (default: 1.0.0)
json (default: 2.1.0)
logger (default: 1.3.0)
matrix (default: 0.1.0)
minitest (5.11.3)
mutex_m (default: 0.1.0)
net-telnet (0.2.0)
openssl (default: 2.1.2)
ostruct (default: 0.1.0)
power_assert (1.1.3)
prime (default: 0.1.0)
psych (default: 3.1.0)
rake (12.3.2)
rdoc (default: 6.1.2)
rexml (default: 3.1.9)
rss (default: 0.2.7)
scanf (default: 1.0.0)
sdbm (default: 1.0.0)
shell (default: 0.7)
stringio (default: 0.0.2)
strscan (default: 1.0.0)
sync (default: 0.5.0)
test-unit (3.2.9)
thwait (default: 0.1.0)
tracer (default: 0.1.0)
webrick (default: 1.4.2)
xmlrpc (0.3.0)
zlib (default: 1.0.0)

(does not contains docker-sync)

If you run the gem install for docker-sync you will use the docker-sync for your rbenv managed ruby.

$ gem install docker-sync